Patent application title: PRODUCTION OF FATTY ACIDS & DERIVATIVES THEREOF
Jay D. Keasling (Berkeley, CA, US)
Zhihao Hu (So. San Francisco, CA, US)
Chris Sommerville (So. San Francisco, CA, US)
George Church (So. San Francisco, CA, US)
David Berry (So. San Francisco, CA, US)
Lisa Friedman (So. San Francisco, CA, US)
Andreas Schirmer (So. San Francisco, CA, US)
Shane Brubaker (So. San Francisco, CA, US)
Stephen B. Del Cardayre (So. San Francisco, CA, US)
IPC8 Class: AC12N100FI
Class name: Liquid fuels (excluding fuels that are exclusively mixtures of liquid hydrocarbons) containing organic -c(=o)o- compound (e.g., fatty acids, etc.) the single bonded oxygen is bonded directly to an additional carbon, which carbon may be single bonded to any element but may be multiple bonded only to carbon (i.e., carboxylic acid esters)
Publication date: 2010-09-30
Patent application number: 20100242345
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Patent application title: PRODUCTION OF FATTY ACIDS & DERIVATIVES THEREOF
Jay D. Keasling
Stephen B. del Cardayre
Origin: SOUTH SAN FRANCISCO, CA US
IPC8 Class: AC12N100FI
Publication date: 09/30/2010
Patent application number: 20100242345
Genetically engineered microorganisms are provided that produce products
from the fatty acid biosynthetic pathway (fatty acid derivatives), as
well as methods of their use.
1. A microorganism comprising:(a) one or more exogenous nucleic acid
sequences encoding at least one peptide selected from accA (EC 184.108.40.206),
accB (EC 220.127.116.11), accC (EC 18.104.22.168), accD (EC 22.214.171.124), aceE (EC
126.96.36.199, 188.8.131.52, 184.108.40.206), aceF (EC 220.127.116.11, 18.104.22.168, 22.214.171.124), acpP
(AAC74178), fadD (EC 126.96.36.199), cer1 (EC 188.8.131.52), fabA (EC184.108.40.206),
fabB (EC 220.127.116.11), fabD (EC 18.104.22.168), fabG (EC 22.214.171.124), fabH (EC
126.96.36.199), fabI (EC 188.8.131.52), fabZ(EC 4.2.1.-), lipase (EC 184.108.40.206),
malonyl-CoA decarboxylase (EC 220.127.116.11, 18.104.22.168), panD (EC 22.214.171.124),
panK (EC 126.96.36.199), pdh (EC 188.8.131.52), and udhA (EC 184.108.40.206);(b) a nucleic
acid sequence encoding a wax synthase (EC 220.127.116.11) or an alcohol
acetyltransferase (EC 18.104.22.168).
5. The microorganism of claim 1, wherein ackA (EC 22.214.171.124), ackB (EC 126.96.36.199), adhE (EC 188.8.131.52, 184.108.40.206), fabF (EC 220.127.116.11), fabR (accession NP--418398), fadE (EC 18.104.22.168, 1.3.99.-), GST (EC 22.214.171.124), gpsA (EC 126.96.36.199), ldhA (EC 188.8.131.52), pflB (EC 184.108.40.206), plsB (EC 220.127.116.11), poxB (EC 18.104.22.168), pta (EC 22.214.171.124), or glutathione synthase (EC 126.96.36.199) is attenuated.
11. The microorganism of claim 1, wherein the microorganism additionally comprises:(a) an exogenous nucleic acid sequence encoding a thioesterase (EC 3.1.2.-, 3.1.1.-);(b) at least one exogenous nucleic acid sequence encoding an enzyme selected from one or more components of the branch chain keto acid dehydrogenase complex (EC 188.8.131.52), llve (EC 184.108.40.206), lpd (EC 220.127.116.11), Ccr (EC1.1.19), IcmA (EC18.104.22.168), IcmB (22.214.171.124), fabH (EC 126.96.36.199), fabF (EC 188.8.131.52), fabH3 (EC 184.108.40.206), fabC3(NP 823468), beta-ketoacyl-ACP synthase II (EC 220.127.116.11), enoyl-CoA reductase (EC 18.104.22.168), enoyl-CoA isomerase (EC 4.2.1.-), and combinations thereof;(c) at least one exogenous nucleic acid sequence encoding an enzyme selected from FabB (EC 22.214.171.124), FabK (EC 126.96.36.199), FabL (EC 188.8.131.52), FabM (EC 184.108.40.206), FadE (EC 220.127.116.11, 1.3.99.-), and combinations thereof;(d) an exogenous nucleic acid sequence encoding ACP, Sfa, or combinations thereof; or(e) an exogenous nucleic acid sequence encoding an enzyme selected from FadA (EC 18.104.22.168), FadI (EC 22.214.171.124), FadB (EC 126.96.36.199), FadJ (EC 188.8.131.52, EC 184.108.40.206, EC 220.127.116.11, EC 18.104.22.168), and combinations thereof.
16. The microorganism of claims 1, wherein accA, accB, accC, accD, or fadD is over-expressed.
17. The microorganism of claims 1, wherein the microorganism is in a vessel comprising a fermentation broth comprising at least 10 mg/L fatty acid ester or at least 10 mg/L wax.
18. A fatty acid derivative produced by the microorganism of claim 1, wherein the fatty acid derivative comprises:(a) from about 1 to about 5 double bonds, a carbon chain length of from about 8 to about 30, about 1 to about 5 branch points, or between 1 and 10 cyclopropyl moieties:(b) an A side and a B side, wherein the A side, the B side, or both the A side and the B side, are produced by the microorganism;(c) an A side and a B side, wherein the A side, the B side, or both the A side and the B side, comprise from about 1 to about 5 double bonds;(d) an A side and a B side, wherein the A side, the B side, or both the A side and the B side, comprise a carbon chain length of from about 1 to about 26;(e) an A side and a B side, wherein the A side, the B side, or both the A side and the B side, comprise from about 1 to about 5 branch points; or(f) an A side and a B side, wherein the A side, the B side, or both the A side and the B side, comprise between 1 and 5 cyclopropyl moieties.
27. The microorganism of claims 1, wherein the microorganism is an E. coli, Arthrobacter sp., Bacillus sp., Botryococcus braunii, Chromatium sp., Cladosporium resina (ATCC22711), Clostridium pasteurianum VKM, Clostridium tenanomorphum, Clostridium acidiurici, Corynebacterium species, cyanobacterial species (Nostoc muscorum, Anacystis (Synechococcus) nidulans, Phormidium luridum, Chlorogloea fritschii, Trichodesmium erythaeum, Oscillatoria williamsii, Microcoleus chthonoplaseis, Coccochloris elabens, Agmenellum quadruplicatum, Plectonema terebrans, M vaginatus, and C. scopulorum), Desulfovibrio desulfuricans (ATCC29577), Kineococcus radiotolerans (BAA-149), Micrococcus luteus (FD533, ATCC 272, 381, 382, ISU, 540, 4698, 7468, 27141), Micrococcus sp. (ATCC 146, 398, 401, 533), Micrococcus roseus (ATCC 412, 416, 516), Micrococcus lysodeikticus, Mycobacterium species, Penicillium sp., Aspergillus sp., Trichoderma virida, Pullularia pullulans, Jeotgalicoccus sp. (M. candicans)(ATCC 8456), Rhodopseudomonas spheroids Chlorobium sp., Rhodospirillium rubrum (ATCC11170), Rhodomicrobium vannielii, Stenotrophomonas maltophilia (ATCC 13637, 17444, 17445, 17666, 17668, 17673, 17674, 17679, 17677), Saccharomycodes ludwigii (ATCC 22711), Saccharomyces sp. (oviformus,ludwiggi, tropicalis), Vibrio furnissii M1, Vibrio marinus MP-1, Vibrio ponticus, Serratia marinorubra, Ustilago maydis, Ustilago nuda, Urocystis agropyri, Sphacelotheca reiliana, or Tilletia sp. (foetida, caries, controversa).
28. A method of producing a fatty acid derivative comprising:(a) culturing the microorganism of claim 1 under conditions sufficient to produce a fatty acid derivative; and(b) separating the fatty acid derivative.
29. The method of claim 28, wherein the microorganism further comprises:(a) an exogenous nucleic acid sequence encoding a thioesterase (EC 3.1.2.-, 3.1.1.-);(b) at least one exogenous nucleic acid sequence encoding an enzyme selected from one or more components of the branch chain keto acid dehydrogenase complex (EC 22.214.171.124), llve (EC 126.96.36.199), lpd (EC 188.8.131.52), Ccr (EC1.1.19), IcmA (EC184.108.40.206), IcmB (220.127.116.11), fabH (EC 18.104.22.168), fabF (EC 22.214.171.124), fabH3 (EC 126.96.36.199), fabC3(NP 823468), beta-ketoacyl-ACP synthase II (EC 188.8.131.52), enoyl-CoA reductase (EC 184.108.40.206), enoyl-CoA isomerase (EC 4.2.1.-), and combinations thereof;(c) at least one exogenous nucleic acid sequence encoding an enzyme selected from FabB (EC 220.127.116.11), FabK (EC 18.104.22.168), FabL (EC 22.214.171.124), FabM (EC 126.96.36.199), FadE (EC 188.8.131.52, 1.3.99.-), and combinations thereof;(d) an exogenous nucleic acid sequence encoding ACP, Sfa, or combinations thereof; or(e) an exogenous nucleic acid sequence encoding an enzyme selected from FadA (EC 184.108.40.206), FadI (EC 220.127.116.11), FadB (EC 18.104.22.168), FadJ (EC 22.214.171.124, EC 126.96.36.199, EC 188.8.131.52, EC 184.108.40.206), and combinations thereof.
30. The method of claim 28, wherein ackA (EC 220.127.116.11), ackB (EC 18.104.22.168), adhE (EC 22.214.171.124, 126.96.36.199), fabF (EC 188.8.131.52), fabR (accession NP 418398), fadE (EC 184.108.40.206, 1.3.99.-), GST (EC 220.127.116.11), gpsA (EC 18.104.22.168), ldhA (EC 22.214.171.124), pflB (EC 126.96.36.199), plsB (EC 188.8.131.52), poxB (EC 184.108.40.206), pta (EC 220.127.116.11), or glutathione synthase (EC 18.104.22.168) of the microorganism is attenuated.
31. The microorganism of claim 1, which produces an increased amount of fatty acid derivatives as compared to the wild-type microorganism.
37. The method of claim 28, wherein separating the fatty acid derivative comprises:allowing the fatty acid derivative to separate into an organic phase; andpurifying the fatty acid derivative from the organic phase.
39. A biofuel composition, comprising:at least about 11% or at least about 17% of a fatty acid derivative, wherein the fatty acid derivative comprises a carbon chain selected from the group consisting of 8:0, 10:0, 12:0, 14:0, 14:1, 16:0, 16:1, 18:0, 18:1, 18:2, 18:3, 20:0, 20:1, 20:2, 20:3, 22:0, 22:1 or 22:3; andat least about 80% conventional diesel fuel.
40. The biofuel composition of claim 39 wherein the-fatty acid derivative has δ13C of from about -10.9 to about -15.4, or a fraction of modern carbon of at least about 1.003.
42. The biofuel composition of claim 40, wherein the fatty acid derivative accounts for at least about 85% of biosourced fatty acid-derived material in the composition.
47. The biofuel composition of claim 39, further comprising a lower alcohol, a surfactant, or a microemulsion in the biofuel composition.
58. The biofuel composition of claim 39, wherein the biofuel comprises less than 0.1% glycerin, or less than 0.1% transesterification catalyst.
60. A fatty acid derivative produced by the method of claim 28.
61. A biofuel composition comprising the fatty acid derivative of claim 60.
62. The biofuel composition of claim 61, comprising at least about 11%, or at least about 17% of the fatty acid derivative, and at least about 80% of conventional diesel fuel.
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of U.S. Provisional Application No. 60/802,016 filed May 19, 2006, U.S. Provisional Application No. 60/801,995 filed May 19, 2006, U.S. Provisional Application 60/908,547 filed Mar. 28, 2007 and PCT application number PCT/US2007/003736 filed Feb. 13, 2007, all of which are herein incorporated by reference.
Genetically engineered microorganisms are provided that produce products from the fatty acid biosynthetic pathway (fatty acid derivatives), as well as methods of their use.
Developments in technology have been accompanied by an increased reliance on fuel sources and such fuel sources are becoming increasingly limited and difficult to acquire. With the burning of fossil fuels taking place at an unprecedented rate, it has likely that the world's fuel demand will soon outweigh the current fuel supplies.
As a result, efforts have been directed toward harnessing sources of renewable energy, such as sunlight, water, wind, and biomass. The use of biomasses to produce new sources of fuel which are not derived from petroleum sources, (i.e. biofuel) has emerged as one alternative option. Biofuel (biodiesel) is a biodegradable, clean-burning combustible fuel made of king chain alkanes and esters. Biodiesel can be used in most internal combustion diesel engines in either a pure form, which is referred to as "neat" biodiesel, or as a mix in any concentration with regular petroleum diesel. Current methods of making biodiesel involve transesterification of triacylglycerides (mainly vegetable oil) which leads to a mixture of fatty acid esters and the unwanted side product glycerin, thus, providing a product that is heterogeneous and a waste product that causes economic inefficiencies.
Disclosed herein are recombinant microorganisms that are capable of synthesizing products derived from the fatty acid biosynthetic pathway (fatty acid derivatives), and optionally releasing such products into the fermentation broth. Such fatty acid derivatives are useful, inter alia, as biofuels and specialty chemicals. These biofuels and specialty chemicals can be used to make additional products, such as nutritional supplements, polymers, paraffin replacements, and personal care products.
The recombinant microorganisms disclosed herein can be engineered to yield various fatty acid derivatives including, but not limited to, short chain alcohols such as ethanol, propanol isopropanol and butanol, fatty alcohols, fatty acid esters, hydrocarbons and wax esters.
In one example, the disclosure provides a method for modifying a microorganism so that it produces, and optionally releases, fatty acid derivatives generated from a renewable carbon source. Such microorganisms are genetically engineered, for example, by introducing an exogenous DNA sequence encoding one or more proteins capable of metabolizing a renewable carbon source to produce, and in some examples secrete, a fatty acid derivative. The modified microorganisms can then be used in a fermentation process to produce useful fatty acid derivatives using the renewable carbon source (biomass) as a starting material. In some examples, an existing genetically tractable microorganism is used because of the ease of engineering its pathways for controlling growth, production and reducing or eliminating side reactions that reduce biosynthetic pathway efficiencies. In addition, such modified microorganisms can be used to consume renewable carbon sources in order to generate fuels that can be directly used as biofuels, without the need for special methods for storage, or transportation. In other examples, microorganisms that naturally produce hydrocarbons are engineered to overproduce hydrocarbons by expressing exogenous nucleic acid sequences that increase fatty acid production.
Provided herein are microorganisms that produce fatty acid derivatives having defined carbon chain length, branching, and saturation levels. In particular examples, the production of homogeneous products decreases the overall cost associated with fermentation and separation. In some examples microorganisms including one or more exogenous nucleic acid sequences encoding at least one thioesterase (EC 22.214.171.124), and at least one wax synthase (EC 126.96.36.199) are provided. In other examples microorganisms are provided that include one or more exogenous nucleic acid sequences encoding at least one thioesterase (EC 188.8.131.52) and at least one alcohol acetyltransferase (184.108.40.206). In yet other examples, microorganisms including one or more exogenous nucleic acid sequences encoding at least one thioesterase (EC 220.127.116.11), at least one acyl-CoA reductase (EC 18.104.22.168) and at least one alcohol dehydrogenase (EC 22.214.171.124) are provided. Microorganisms expressing one or more exogenous nucleic acid sequences encoding at least one thioesterase (EC 126.96.36.199) and at least one fatty alcohol forming acyl-CoA reductase (1.1.1.*) are also provided. The thioesterase peptides encoded by the exogenous nucleic acid sequences can be chosen to provide homogeneous products.
In some examples the microorganism that is engineered to produce the fatty acid derivative is E. coli, Z. mobilis, Rhodococcus opacus, Ralstonia eutropha, Vibrio furnissii, Saccharomyces cerevisiae, Lactococcus lactis, Streptomycetes, Stenotrophomonas maltophila, Pseudomonas or Micrococus leuteus and their relatives.
In other examples microorganisms that produce hydrocarbons endogenously can be engineered to overproduce hydrocarbons by optimizing the fatty acid biosynthetic pathway as described herein. Exemplary microorganisms that are known to produce hydrocarbons and can be engineered to over-produce hydrocarbons using the teachings provided herein include Arthrobacter sp., Bacillus sp., Botryococcus braunii, Chromatium sp., Cladosporium resina (ATCC22711), Clostridium pasteurianum VKM, Clostridium tenanomorphum, Clostridium acidiurici, Corynebacterium species, cyanobacterial species (Nostoc muscorum, Anacystis (Synechococcus) nidulans, Phormidium luridum, Chlorogloea Trichodesmium erythaeum, Oscillatoria williamsii, Microcoleus chthonoplaseis, Coccochloris elabens, Agmenellum quadruplicatum, Plectonema terebrans, M vaginatus, and C. scopulorum), Desulfovibrio desulfuricans (ATCC29577), Kineococcus radiotolerans (BAA-149), Micrococcus luteus (FD533, ATCC 272, 381, 382, ISU, 540, 4698, 7468, 27141), Micrococcus sp. (ATCC 146, 398, 401, 533), Micrococcus roseus (ATCC 412, 416, 516), Micrococcus lysodeikticus, Mycobacterium species, Penicillium sp., Aspergillus sp., Trichoderma virida, Pullularia pullulans, Jeotgalicoccus sp. (M. candicans)(ATCC 8456), Rhodopseudomonas spheroids Chlorobium sp., Rhodospirillium rubrum (ATCC11170), Rhodomicrobium vannielii, Stenotrophomonas maltophilia (ATCC 13637, 17444, 17445, 17666, 17668, 17673, 17674, 17679, 17677), Saccharomycodes ludwigii (ATCC 22711), Saccharomyces sp. (oviformus,ludwiggi, tropicalis), Vibrio furnissii M1, Vibrio marinus MP-1, Vibrio ponticus, Serratia marinorubra, Ustilago maydis, Ustilago nuda, Urocystis agropyri, Sphacelotheca reiliana, and Tilletia sp. (foetida, caries, controversa).
In addition to being engineered to express exogenous nucleic acid sequences that allow for the production of fatty acid derivatives, the microorganism can additionally have one or more endogenous genes functionally deleted or attenuated. For example, ackA (EC 188.8.131.52), ackB (EC 184.108.40.206), adhE. (EC 220.127.116.11, 18.104.22.168), fabF (EC 22.214.171.124), fabR (accession NP--418398), fadE (EC 126.96.36.199, 1.3.99.-), GST (EC 188.8.131.52), gpsA (EC 184.108.40.206), ldhA (EC 220.127.116.11), pflB (EC 18.104.22.168), plsB (EC 22.214.171.124), poxB (EC 126.96.36.199), pta (EC 188.8.131.52), glutathione synthase (EC 184.108.40.206) and combinations thereofcan be attenuated.
In addition to being engineered to express exogenous nucleic acid sequences that allow for the production of fatty acid derivatives, the microorganism can additionally have one or more additional genes over-expressed. For example, pdh, panK, aceEF (encoding the E1p dehydrogenase component and the E2p dihydrolipoamide acyltransferase component of the pyruvate and 2-oxoglutarate dehydrogenase complexes, Accessions: NP--414656, NP--414657, EC: 220.127.116.11. 18.104.22.168, 22.214.171.124), accABCD/fabH/fabD/fabG/acpP/fabF (encoding FAS, Accessions: CAD85557, CAD85558, NP--842277, NP--841683, NP--415613, EC: 126.96.36.199, 188.8.131.52, 184.108.40.206, 220.127.116.11, 18.104.22.168), genes encoding fatty-acyl-coA reductases (Accessions: AAC45217, EC 1.2.1.-), UdhA or similar genes (encoding pyridine nucleotide transhydrogenase, Accession: CAA46822 , EC:22.214.171.124) and genes encoding fatty-acyl-coA reductases (Accessions: AAC45217, EC 1.2.1.-).
In some examples, the microorganisms described herein produce at least 1 mg of fatty acid derivative per liter fermentation broth. In other examples the microorganisms produce at least 100 mg/L, 500 mg/L, 1 g/L, 5 g/L, 10 g/L, 20 g/L, 25 g/L, 30 g/L, 35 g/L, 40 g/L, 50 g/L, 100 g/L, or 120 g/L of fatty acid derivative per liter fermentation broth. In some examples, the fatty acid derivative is produced and released from the microorganism and in yet other examples the microorganism is lysed prior to separation of the product.
In some examples, the fatty acid derivative includes a carbon chain that is at least 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, or 34 carbons long. In some examples at least 50%, 60%, 70%, 80%, 85%, 90%, or 95% of the fatty acid derivative product made contains a carbon chain that is 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, or 34 carbons long. In yet other examples, at least 60%, 70%, 80%, 85%, 90%, or 95% of the fatty acid derivative product contain 1, 2, 3, 4, or 5, points of unsaturation
Also provided are methods of producing fatty acid derivatives. These methods include culturing the microorganisms described herein and separating the product from the fermentation broth.
These and other examples are described further in the following detailed description.
BRIEF DESCRIPTION OF THE FIGURES
FIG. 1 shows the FAS biosynthetic pathway.
FIG. 2 shows biosynthetic pathways that produce waxes. Waxes can be produced in a host cell using alcohols produced within the host cell or they can be produced by adding exogenous alcohols in the medium. A microorganism designed to produce waxes will produce wax synthase enzymes (EC 126.96.36.199) using exogenous nucleic acid sequences as well as thioesterase (EC 188.8.131.52) sequences. Other enzymes that can be also modulated to increase the production of waxes include enzymes involved in fatty acid synthesis (FAS enzymes EC 184.108.40.206), acyl-CoA synthase (EC 220.127.116.11), fatty alcohol forming acyl-CoA reductase (EC 1.1.1.*), acyl-CoA reductase (18.104.22.168) and alcohol dehydrogenase (EC 22.214.171.124).
FIG. 3 shows biosynthetic pathways that produce fatty alcohols. Fatty alcohols having defined carbon chain lengths can be produced by expressing exogenous nucleic acid sequences encoding thioesterases (EC 126.96.36.199), and combinations of acyl-CoA reductases (EC 188.8.131.52), alcohol dehydrogenases (EC 184.108.40.206) and fatty alcohol forming acyl-CoA reductases (FAR, EC 1.1.1*). Other enzymes that can be also modulated to increase the production of fatty alcohols include enzymes involved in fatty acid synthesis (FAS enzymes EC 220.127.116.11), and acyl-CoA synthase (EC 18.104.22.168).
FIG. 4 shows biosynthetic pathways that produce fatty acids esters. Fatty acids esters having defined carbon chain lengths can be produced by exogenously expressing various thioesterases (EC 22.214.171.124), combinations of acyl-CoA reductase (126.96.36.199), alcohol dehydrogenases (EC 188.8.131.52), and fatty alcohol forming Acyl-CoA reductase (FAR, EC 1.1.1*), as well as, acetyl transferase (EC 184.108.40.206). Other enzymes that can be modulated to increase the production of fatty acid esters include enzymes involved in fatty acid synthesis (FAS enzymes EC 220.127.116.11), and acyl-CoA synthase (EC 18.104.22.168).
FIG. 5 shows fatty alcohol production by the strain described in Example 4, co-transformed with pCDFDuet-1-fadD-acr1 and plasmids containing various thioesterase genes. The strains were grown aerobically at 25° C. in M9 mineral medium with 0.4% glucose in shake flasks. Saturated C10, C12, C14, C16 and C18 fatty alcohol were identified. Small amounts of C16:1 and C18:1 fatty alcohols were also detected in some samples. Fatty alcohols were extracted from cell pellets using ethyl acetate and derivatized with N-trimethylsilyl (TMS) imidazole to increase detection.
FIG. 6 shows the release of fatty alcohols from the production strain. Approximately 50% of the fatty alcohol produced was released from the cells when they were grown at 37° C.
FIGS. 7A-7D show GS-MS spectrum of octyl octanoate (C8C8) produced by a production hosts expressing alcohol acetyl transferase (AATs, EC 22.214.171.124) and production hosts expressing wax synthase (EC 126.96.36.199). FIG. 7A shows acetyl acetate extract of strain C41(DE3, ΔfadE/pHZ1.43)/pRSET B+pAS004.114B) wherein the pHZ1.43 plasmid expressed ADP1 (wax synthase). FIG. 7B shows acetyl acetate extract of strain C41(DE3, ΔfadE/pHZ1.43)/pRSET B+pAS004.114B) wherein the pHZ1.43 plasmid expressed SAAT. FIG. 7C shows acetyl acetate extract of strain C41(DE3, ΔfadE/pHZ1.43)/pRSET B+pAS004.114B) wherein the pHZ1.43 plasmid did not contain ADP1 (wax synthase) or SAAT. FIG. 7D shows the mass spectrum and fragmentation pattern of C8C8 produced by C41(DE3, ΔfadE/pHZ1.43)/pRSET B+pAS004.114B) wherein the pHZ1.43 plasmid expressed SAAT).
FIG. 8 shows the distribution of ethyl esters made when the wax synthase from A. baylyi ADP1 (WSadp1) was co-expressed with thioesterase gene from Cuphea hookeriana in a production host.
FIGS. 9A and 9B show chromatograms of GC/MS analysis. FIG. 9A shows a chromatogram of the ethyl extract of the culture of E. coil LS9001 strain transformed with plasmids pCDFDuet-1-fadD-WSadp1, pETDuet-1-'tesA. Ethanol was fed to fermentations. FIG. 9B shows a chromatogram of ethyl hexadecanoate and ethyl oleate used as reference.
FIG. 10 shows a table that identifies various genes that can be over-expressed or attenuated to increase fatty acid derivative production. The table also identifies various genes that can be modulated to alter the structure of the fatty acid derivative product. One of ordinary skill in the art will appreciate that some of the genes that are used to alter the structure of the fatty acid derivative will also increase the production of fatty acid derivatives.
ABBREVIATIONS AND TERMS
The following explanations of terms and methods are provided to better describe the present disclosure and to guide those of ordinary skill in the art in the practice of the present disclosure. As used herein, "comprising" means "including" and the singular forms "a" or "an" or "the" include plural references unless the context clearly dictates otherwise. For example, reference to "comprising a cell" includes one or a plurality of such cells, and reference to "comprising the thioesterase" includes reference to one or more thioesterase peptides and equivalents thereof known to those of ordinary skill in the art, and so forth. The term "or" refers to a single element of stated alternative elements or a combination of two or more elements, unless the context clearly indicates otherwise. For example, the phrase "thioesterase activity or fatty alcohol-forming acyl-CoA reductase activity" refers to thioesterase activity, fatty alcohol forming acyl-CoA reductase activity, or a combination of both fatty alcohol forming acyl-CoA reductase activity, and thioesterase activity.
Unless explained otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this disclosure belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present disclosure, suitable methods and materials are described below. The materials, methods, and examples are illustrative only and not intended to be limiting. Other features of the disclosure are apparent from the following detailed description and the claims.
Accession Numbers: The accession numbers throughout this description are derived from the NCBI database (National Center for Biotechnology Information) maintained by the National Institute of Health, U.S.A. The accession numbers are as provided in the database on Mar. 27, 2007.
Enzyme Classification Numbers (EC): The EC numbers provided throughout this description are derived from the KEGG Ligand database, maintained by the Kyoto Encyclopedia of Genes and Genomics, sponsored in part by the University of Tokyo. The EC numbers are as provided in the database on Mar. 27, 2007.
Attenuate: To lessen the impact, activity or strength of something. In one example, the sensitivity of a particular enzyme to-feedback inhibition or inhibition caused by a composition that is not a product or a reactant (non-pathway specific feedback) is lessened such that the enzyme activity is not impacted by the presence of a compound. For example, the fabH gene and its corresponding amino acid sequence are temperature sensitive and can be altered to decrease the sensitivity to temperature fluctuations. The attenuation of the fabH gene can be used when branched amino acids are desired. In another example, an enzyme that has been altered to be less active can be referred to as attenuated.
A functional deletion of an enzyme can be used to attenuate an enzyme. A functional deletion is a mutation, partial or complete deletion, insertion, or other variation made to a gene sequence or a sequence controlling the transcription of a gene sequence, which reduces or inhibits production of the gene product, or renders the gene product non-functional (i.e. the mutation described herein for the plsB gene). For example, functional deletion of fabR in E. coli reduces the repression of the fatty acid biosynthetic pathway and allows E. coli to produce more unsaturated fatty acids (UFAs). In some instances a functional deletion is described as a knock-out mutation.
One of ordinary skill in the art will appreciate that there are many methods of attenuating a enzyme activity. For example, attenuation can be accomplished by introducing amino acid sequence changes via altering the nucleic acid sequence, placing the gene under the control of a less active promoter, expressing interfering RNA, ribozymes or antisense sequences that targeting the gene of interest, or through any other technique known in the art.
Carbon source: Generally refers to a substrate or compound suitable to be used as a source of carbon for prokaryotic or simple eukaryotic cell growth. Carbon sources can be in various forms, including, but not limited to polymers, carbohydrates, acids, alcohols, aldehydes, ketones, amino acids, peptides, etc. These include, for example, various monosaccharides such as glucose, oligosaccharides, polysaccharides, cellulosic material, xylose, and arabinose, disaccharides, such sucrose, saturated or unsaturated fatty acids, succinate, lactate, acetate, ethanol, etc., or mixtures thereof. The carbon source can additionally be a product of photosynthesis, including, but not limited to glucose.
cDNA (complementary DNA): A piece of DNA lacking internal, non-coding segments (introns) and regulatory sequences which determine transcription. cDNA can be synthesized by reverse transcription from messenger RNA extracted from cells.
Deletion: The removal of one or more nucleotides from a nucleic acid molecule or one or more amino acids from a protein, the regions on either side being joined together.
Detectable: Capable of having an existence or presence ascertained. For example, production of a product from a reactant, for example, the production of C18 fatty acids, is detectable using the method provided in Example 11 below.
DNA: Deoxyribonucleic acid. DNA is a long chain polymer which includes the genetic material of most living organisms (some viruses have genes including ribonucleic acid, RNA). The repeating units in DNA polymers are four different nucleotides, each of which includes one of the four bases, adenine, guanine, cytosine and thymine bound to a deoxyribose sugar to which a phosphate group is attached. Triplets of nucleotides, referred to as codons, in DNA molecules code for amino acid in a peptide. The term codon is also used for the corresponding (and complementary) sequences of three nucleotides in the mRNA into which the DNA sequence is transcribed.
Endogenous: As used herein with reference to a nucleic acid molecule and a particular cell or microorganism refers to a nucleic acid sequence or peptide that is in the cell and was not introduced into the cell using recombinant engineering techniques. For example, a gene that was present in the cell when the cell was originally isolated from nature. A gene is still considered endogenous if the control sequences, such as a promoter or enhancer sequences that activate transcription or translation have been altered through recombinant techniques.
Exogenous: As used herein with reference to a nucleic acid molecule and a particular cell refers to any nucleic acid molecule that does not originate from that particular cell as found in nature. Thus, a non-naturally-occurring nucleic acid molecule is considered to be exogenous to a cell once introduced into the cell. A nucleic acid molecule that is naturally-occurring also can be exogenous to a particular cell. For example, an entire coding sequence isolated from cell X is an exogenous nucleic acid with respect to cell Y once that coding sequence is introduced into cell Y, even if X and Y are the same cell type.
Expression: The process by which a gene's coded information is converted into the structures and functions of a cell, such as a protein, transfer RNA, or ribosomal RNA. Expressed genes include those that are transcribed into mRNA and then translated into protein and those that are transcribed into RNA but not translated into protein (for example, transfer and ribosomal RNAs).
Fatty ester: Includes any ester made from a fatty acid. The carbon chains in fatty acids can contain any combination of the modifications described herein. For example, the carbon chain can contain one or more points of unsaturation, one or more points of branching, including cyclic branching, and can be engineered to be short or long. Any alcohol can be used to form fatty acid esters, for example alcohols derived from the fatty acid biosynthetic pathway, alcohols produced by the production host through non-fatty acid biosynthetic pathways, and alcohols that are supplied in the fermentation broth.
Fatty acid derivative: Includes products made in part from the fatty acid biosynthetic pathway of the host organism. The fatty acid biosynthetic pathway includes fatty acid synthase enzymes which can be engineered as described herein to produce fatty acid derivatives, and in some examples can be expressed with additional enzymes to produce fatty acid derivatives having desired carbon chain characteristics. Exemplary fatty acid derivatives include for example, short and long chain alcohols, hydrocarbons, and fatty acid esters including waxes.
Fermentation Broth: Includes any medium which supports microorganism life (i.e. a microorganism that is actively metabolizing carbon). A fermentation medium usually contains a carbon source. The carbon source can be anything that can be utilized, with or without additional enzymes, by the microorganism for energy.
Hydrocarbon: includes chemical compounds that containing the elements carbon (C) and hydrogen (H). All hydrocarbons consist of a carbon backbone and atoms of hydrogen attached to that backbone. Sometimes, the term is used as a shortened form of the term "aliphatic hydrocarbon." There are essentially three types of hydrocarbons: (1) aromatic hydrocarbons, which have at least one aromatic ring; (2) saturated hydrocarbons, also known as alkanes, which lack double, triple or aromatic bonds; and (3) unsaturated hydrocarbons, which have one or more double or triple bonds between carbon atoms, are divided into: alkenes, alkynes, and dienes. Liquid geologically-extracted hydrocarbons are referred to as petroleum (literally "rock oil") or mineral oil, while gaseous geologic hydrocarbons are referred to as natural gas. All are significant sources of fuel and raw materials as a feedstock for the production of organic chemicals and are commonly found in the Earth's subsurface using the tools of petroleum geology. Oil reserves in sedimentary rocks are the principal source of hydrocarbons for the energy and chemicals industries. Hydrocarbons are of prime economic importance because they encompass the constituents of the major fossil fuels (coal, petroleum, natural gas, etc.) and biofuels, as well as plastics, waxes, solvents and oils.
Isolated: An "isolated" biological component (such as a nucleic acid molecule, protein, or cell) has been substantially separated or purified away from other biological components in which the component naturally occurs, such as other chromosomal and extrachromosomal DNA and RNA, and proteins. Nucleic acid molecules and proteins that have been "isolated" include nucleic acid molecules and proteins purified by standard purification methods. The term also embraces nucleic acid molecules and proteins prepared by recombinant expression in a host cell as well as chemically synthesized nucleic acid molecules and proteins.
In one example, isolated refers to a naturally-occurring nucleic acid molecule that is not immediately contiguous with both of the sequences with which it is immediately contiguous (one on the 5' end and one on the 3' end) in the naturally-occurring genome of the organism from which it is derived.
Microorganism: Includes prokaryotic and eukaryotic microbial species from the Domains Archaea, Bacteria and Eucarya, the latter including yeast and filamentous fungi, protozoa, algae, or higher Protista. The terms "microbial cells" and "microbes" are used interchangeably with the term microorganism.
Nucleic Acid Molecule: Encompasses both RNA and DNA molecules including, without limitation, cDNA, genomic DNA, and mRNA. Includes synthetic nucleic acid molecules, such as those that are chemically synthesized or recombinantly produced. The nucleic acid molecule can be double-stranded or single-stranded. Where single-stranded, the nucleic acid molecule can be the sense strand or the antisense strand. In addition, nucleic acid molecule can be circular or linear.
Operably linked: A first nucleic acid sequence is operably linked with a second nucleic acid sequence when the first nucleic acid sequence is placed in a functional relationship with the second nucleic acid sequence. For instance, a promoter is operably linked to a coding sequence if the promoter affects the transcription or expression of the coding sequence. Generally, operably linked DNA sequences are contiguous and, where necessary to join two protein coding regions, in the same reading frame. Configurations of separate genes that are transcribed in tandem as a single messenger RNA are denoted as operons. Thus placing genes in close proximity, for example in a plasmid vector, under the transcriptional regulation of a single promoter, constitutes a synthetic operon.
ORF (open reading frame): A series of nucleotide triplets (codons) coding for amino acids without any termination codons. These sequences are usually translatable into a peptide.
Over-expressed: When a gene is caused to be transcribed at an elevated rate compared to the endogenous transcription rate for that gene. In some examples, over-expression additionally includes an elevated rate of translation of the gene compared to the endogenous translation rate for that gene. Methods of testing for over-expression are well known in the art, for example transcribed RNA levels can be assessed using rtPCR and protein levels can be assessed using SDS page gel analysis.
Purified: The term purified does not require absolute purity; rather, it is intended as a relative term. Thus, for example, a purified fatty acid derivative preparation, such as a wax, or a fatty acid ester preparation, is one in which the product is more concentrated than the product is in its environment within a cell. For example, a purified wax is one that is substantially separated from cellular components (nucleic acids, lipids, carbohydrates, and other peptides) that can accompany it. In another example, a purified wax preparation is one in which the wax is substantially-free from contaminants, such as those that might be present following fermentation.
In one example, a fatty acid ester is purified when at least about 50% by weight of a sample is composed of the fatty acid ester, for example when at least about 60%, 70%, 80%, 85%, 90%, 92%, 95%, 98%, or 99% or more of a sample is composed of the fatty acid ester. Examples of methods that can be used to purify a waxes, fatty alcohols, and fatty acid esters, include the methods described in Example 11 below.
Recombinant: A recombinant nucleic acid molecule or protein is one that has a sequence that is not naturally occurring, has a sequence that is made by an artificial combination of two otherwise separated segments of sequence, or both. This artificial combination can be achieved, for example, by chemical synthesis or by the artificial manipulation of isolated segments of nucleic acid molecules or proteins, such as genetic engineering techniques. Recombinant is also used to describe nucleic acid molecules that have been artificially manipulated, but contain the same regulatory sequences and coding regions that are found in the organism from which the nucleic acid was isolated. A recombinant cell or microorganism is one that contains an exogenous nucleic acid molecule, such as a recombinant nucleic acid molecule.
Release: The movement of a compound from inside a cell (intracellular) to outside a cell (extracellular). The movement can be active or passive. When release is active it can be facilitated by one or more transporter peptides and in some examples it can consume energy. When release is passive, it can be through diffusion through the membrane and can be facilitated by continually collecting the desired compound from the extracellular environment, thus promoting further diffusion. Release of a compound can also be accomplished by lysing a cell.
Surfactants: Substances capable of reducing the surface tension of a liquid in which they are dissolved. They are typically composed of a water-soluble head and a hydrocarbon chain or tail. The water soluble group is hydrophilic and can be either ionic or nonionic, and the hydrocarbon chain is hydrophobic. Surfactants are used in a variety of products, including detergents and cleaners, and are also used as auxiliaries for textiles, leather and paper, in chemical processes, in cosmetics and pharmaceuticals, in the food industry and in agriculture. In addition, they can be used to aid in the extraction and isolation of crude oils which are found hard to access environments or as water emulsions.
There are four types of surfactants characterized by varying uses. Anionic surfactants have detergent-like activity and are generally used for cleaning applications. Cationic surfactants contain long chain hydrocarbons and are often used to treat proteins and synthetic polymers or are components of fabric softeners and hair conditioners. Amphoteric surfactants also contain long chain hydrocarbons and are typically used in shampoos. Non-ionic surfactants are generally used in cleaning products.
Transformed or recombinant cell: A cell into which a nucleic acid molecule has been introduced, such as an acyl-CoA synthase encoding nucleic acid molecule, for example by molecular biology techniques. Transformation encompasses all techniques by which a nucleic acid molecule can be introduced into such a cell, including, but not limited to, transfection with viral vectors, conjugation, transformation with plasmid vectors, and introduction of naked DNA by electroporation, lipofection, and particle gun acceleration.
Under conditions that permit product production: Any fermentation conditions that allow a microorganism to produce a desired product, such as fatty acids, hydrocarbons, fatty alcohols, waxes, or fatty acid esters. Fermentation conditions usually include temperature ranges, levels of aeration, and media selection, which when combined allow the microorganism to grow. Exemplary mediums include broths or gels. Generally, the medium includes a carbon source such as glucose, fructose, cellulose, or the like that can be metabolized by the microorganism directly, or enzymes can be used in the medium to facilitate metabolizing the carbon source. To determine if culture conditions permit product production, the microorganism can be cultured for 24, 36, or 48 hours and a sample can be obtained and analyzed. For example, the cells in the sample or the medium in which the cells were grown can be tested for the presence of the desired product. When testing for the presence of a product assays, such as those provided in the Examples below, can be used.
Vector: A nucleic acid molecule as introduced into a cell, thereby producing a transformed cell. A vector can include nucleic acid sequences that permit it to replicate in the cell, such as an origin of replication. A vector can also include one or more selectable marker genes and other genetic elements known in the art.
Wax: A variety of fatty acid esters which form solids or pliable substances under an identified set of physical conditions. Fatty acid esters that are termed waxes generally have longer carbon chains than fatty acid esters that are not waxes. For example, a wax generally forms a pliable substance at room temperature.
I. Production of Fatty Acid Derivatives
The host organism that exogenous DNA sequences are transformed into can be a modified host organism, such as an organism that has been modified to increase the production of acyl-ACP or acyl-CoA, reduce the catabolism of fatty acid derivatives and intermediates, or to reduce feedback inhibition at specific points in the biosynthetic pathway. In addition to modifying the genes described herein additional cellular resources can be diverted to over produce fatty acids, for example the lactate, succinate and/or acetate pathways can be attenuated, and acetyl-CoA carboxylase (ACC) can be over expressed. The modifications to the production host described herein can be through genomic alterations, extrachromosomal expression systems, or combinations thereof. An overview of the pathway is provided in FIGS. 1 and 2.
A. Acetyl-CoA--Malonyl-CoA to Acyl-ACP
Fatty acid synthase (FAS) is a group of peptides that catalyze the initiation and elongation of acyl chains (Marrakchi et al., Biochemical Society, 30:1050-1055, 2002). The acyl carrier protein (ACP) along with the enzymes in the FAS pathway control the length, degree of saturation and branching of the fatty acids produced. Enzymes that can be included in FAS include AccABCD, FabD, FabH, FabG, FabA, FabZ, FabI, FabK, FabL, FabM, FabB, and FabF. Depending upon the desired product one or more of these genes can be attenuated or over-expressed.
For example, the fatty acid biosynthetic pathway in the production host suses the precursors acetyl-CoA and malonyl-CoA (FIG. 2). E. coli or other host organisms engineered to overproduce these components can serve as the starting point for subsequent genetic engineering steps to provide the specific output product (such as, fatty acid esters, hydrocarbons, fatty alcohols). Several different modifications can be made, either in combination or individually, to the host strain to obtain increased acetyl CoA/malonyl CoA/fatty acid and fatty acid derivative production. For example, to increase acetyl CoA production, a plasmid with pdh, panK, aceEF, (encoding the E1p dehydrogenase component and the E2p dihydrolipoamide acyltransferase component of the pyruvate and 2-oxoglutarate dehydrogenase complexes), fabH/fabD/fabG/acpP/fabF, and in some examples additional DNA encoding fatty-acyl-CoA reductases and aldehyde decarbonylases, all under the control of a constitutive, or otherwise controllable promoter, can be constructed. Exemplary Genbank accession numbers for these genes are: pdh (BAB34380, AAC73227, AAC73226), panK (also known as coaA, AAC76952), aceEF (AAC73227, AAC73226), fabH(AAC74175), fabD (AAC74176), fabG (AAC74177), acpP (AAC74178), fabF (AAC74179).
Additionally, fadE, gpsA, ldhA, pflb, adhE, pta, poxB, ackA, and/or ackB can be knocked-out, or their expression levels can be reduced, in the engineered microorganism by transformation with conditionally replicative or non-replicative plasmids containing null or deletion mutations of the corresponding genes, or by substituting promoter or enhancer sequences. Exemplary Genbank accession numbers for these genes are; fadE (AAC73325), gspA (AAC76632), ldhA (AAC74462), pflb (AAC73989), adhE (AAC74323), pta (AAC75357), poxB (AAC73958), ackA (AAC75356), and ackB (BAB81430).
The resulting engineered microorganisms can be grown in a desired environment, for example one with limited glycerol (less than 1% w/v in the culture medium). As such, these microorganisms will have increased acetyl-CoA production levels. Malonyl-CoA overproduction can be effected by engineering the microorganism as described above, with DNA encoding accABCD (acetyl CoA carboxylase, for example accession number AAC73296, EC 188.8.131.52) included in the plasmid synthesized de novo. Fatty acid overproduction can be achieved by further including DNA encoding lipase (for example Accessions numbers CAA89087, CAA98876) in the plasmid synthesized de novo.
In some examples, acetyl-CoA carboxylase (ACC) is over-expressed to increase the intracellular concentration thereof by at least 2-fold, such as at least 5-fold, or at least 10-fold, for example relative to native expression levels.
In addition, the plsB (for example Accession number AAC77011) D311E mutation can be used to remove limitations on the pool of acyl-CoA.
In addition, over-expression of an sfa gene (suppressor of FabA, for example Accession number AAN79592) can be included in the production host to increase production of monounsaturated fatty acids (Rock et al., J. Bacteriology 178:5382-5387, 1996).
B. Acyl-ACP to Fatty Acid
To engineer a production host for the production of a homogeneous population of fatty acid derivatives, one or more endogenous genes can be attenuated or functionally deleted and one or more thioesterases can be expressed. For example, C10 fatty acid derivatives can be produced by attenuating thioesterase C18 (for example accession numbers AAC73596 and P0ADA1), which uses C18:1-ACP and expressing thioesterase C10 (for example accession number Q39513), which uses C10-ACP. Thus, resulting in a relatively homogeneous population of fatty acid derivatives that have a carbon chain length of 10. In another example, C14 fatty acid derivatives can be produced by attenuating endogenous thioesterases that produce non-C14 fatty acids and expressing the thioesterase accession number Q39473 (which uses C14-ACP). In yet another example, C12 fatty acid derivatives can be produced by expressing thioesterases that use C12-ACP (for example accession number Q41635) and attenuating thioesterases that produce non-C12 fatty acids. Acetyl CoA, malonyl CoA, and fatty acid overproduction can be verified using methods known in the art, for example by using radioactive precursors, HPLC, and GC-MS subsequent to cell lysis.
TABLE-US-00001 TABLE 1 Thioesterases Preferential Accession product Number Source Organism Gene produced AAC73596 E. coli tesA without leader C18:1 sequence Q41635 Umbellularia fatB C12:0 california Q39513; Cuphea hookeriana fatB2 C8:0-C10:0 AAC49269 Cuphea hookeriana fatB3 C14:0-C16:0 Q39473 Cinnamonum fatB C14:0 camphorum CAA85388 Arabidopsis thaliana fatB[M141T]* C16:1 NP 189147; Arabidopsis thaliana fatA C18:1 NP 193041 CAC39106 Bradyrhiizobium fatA C18:1 japonicum AAC72883 Cuphea hookeriana fatA C18:1 *Mayer et al., BMC Plant Biology 7: 1-11, 2007.
C. Fatty Acid to Acyl-CoA
Production hosts can be engineered using known peptides to produce fatty acids of various lengths. One method of making fatty acids involves increasing the expression of, or expressing more active forms of, one or more acyl-CoA synthase peptides (EC 184.108.40.206).
As used herein, acyl-CoA synthase includes peptides in enzyme classification number EC 220.127.116.11, as well as any other peptide capable of catalyzing the conversion of a fatty acid to acyl-CoA. Additionally, one of ordinary skill in the art will appreciate that some acyl-CoA synthase peptides will catalyze other reactions as well, for example some acyl-CoA synthase peptides will accept other substrates in addition to fatty acids. Such non-specific acyl-CoA synthase peptides are, therefore, also included. Acyl-CoA synthase peptide sequences are publicly available. Exemplary GenBank Accession Numbers are provided in FIG. 10.
D. Acyl-CoA to Fatty Alcohol
Production hosts can be engineered using known polypeptides to produce fatty alcohols from acyl-CoA. One method of making fatty alcohols involves increasing the expression of or expressing more active forms of fatty alcohol forming acyl-CoA reductase (FAR, EC 1.1.1.*), or acyl-CoA reductases (EC 18.104.22.168) and alcohol dehydrogenase (EC 22.214.171.124). Hereinafter fatty alcohol forming acyl-CoA reductase (FAR, EC 1.1.1.*), acyl-CoA reductases (EC 126.96.36.199) and alcohol dehydrogenase (EC 188.8.131.52) are collectively referred to as fatty alcohol forming peptides. In some examples all three of the fatty alcohol forming genes can be over expressed in a production host, and in yet other examples one or more of the fatty alcohol forming genes can be over-expressed.
As used herein, fatty alcohol forming peptides include peptides in enzyme classification numbers EC 1.1.1.*, 184.108.40.206, and 220.127.116.11, as well as any other peptide capable of catalyzing the conversion of acyl-CoA to fatty alcohol. Additionally, one of ordinary skill in the art will appreciate that some fatty alcohol forming peptides will catalyze other reactions as well, for example some acyl-CoA reductase peptides will accept other substrates in addition to fatty acids. Such non-specific peptides are, therefore, also included. Fatty alcohol forming peptides sequences are publicly available. Exemplary GenBank Accession Numbers are provided in FIG. 10.
Fatty alcohols can also be described as hydrocarbon-based surfactants. For surfactant production the microorganism is modified so that it produces a surfactant from a renewable carbon source. Such a microorganism includes a first exogenous DNA sequence encoding a protein capable of converting a fatty acid to a fatty aldehyde and a second exogenous DNA sequence encoding a protein capable of converting a fatty aldehyde to an alcohol. In some examples, the first exogenous DNA sequence encodes a fatty acid reductase. In one embodiment, the second exogenous DNA sequence encodes mammalian microsomal aldehyde reductase or long-chain aldehyde dehydrogenase. In a further example, the first and second exogenous DNA sequences are from a multienzyme complex from Arthrobacter AK 19, Rhodotorula glutinins, Acinobacter sp strain M-1, or Candida lipolytica. In one embodiment, the first and second heterologous DNA sequences are from a multienzyme complex from Acinobacter sp strain M-1 or Candida lipolytica.
Additional sources of heterologous DNA sequences encoding fatty acid to long chain alcohol converting proteins that can be used in surfactant production include, but are not limited to, Mortierella alpina (ATCC 32222), Crytococcus curvatus, (also referred to as Apiotricum curvatum), Alcanivorax jadensis (T9T=DSM 12718=ATCC 700854), Acinetobacter sp. HO1-N, (ATCC 14987) and Rhodococcus opacus (PD630 DSMZ 44193).
In one example, the fatty acid derivative is a saturated or unsaturated surfactant product having a carbon atom content limited to between 6 and 36 carbon atoms. In another example, the surfactant product has a carbon atom content limited to between 24 and 32 carbon atoms.
Appropriate hosts for producing surfactants can be either eukaryotic or prokaryotic microorganisms. Exemplary hosts include Arthrobacter AK 19, Rhodotorula glutinins, Acinobacter sp strain M-1, Arabidopsis thalania, or Candida lipolytica, Saccharomyces cerevisiae, and E. coli engineered to express acetyl CoA carboxylase. Hosts which demonstrate an innate ability to synthesize high levels of surfactant precursors in the form of lipids and oils, such as Rhodococcus opacus, Arthrobacter AK 19, Rhodotorula glutinins E. coli engineered to express acetyl CoA carboxylase, and other oleaginous bacteria, yeast, and fungi can also be used.
E. Fatty Alcohols to Fatty Esters
Production hosts can be engineered using known polypeptides to produce fatty esters of various lengths. One method of making fatty esters includes increasing the expression of, or expressing more active forms of, one or more alcohol O-acetyltransferase peptides (EC 18.104.22.168). These peptides catalyze the reaction of acetyl-CoA and an alcohol to form CoA and an acetic ester. In some examples the alcohol O-acetyltransferase peptides can be expressed in conjunction with selected thioesterase peptides, FAS peptides and fatty alcohol forming peptides, thus, allowing the carbon chain length, saturation and degree of branching to be controlled. In some cases the bkd operon can be coexpressed to enable branched fatty acid precursors to be produced.
As used herein, alcohol O-acetyltransferase peptides include peptides in enzyme classification number EC 22.214.171.124, as well as any other peptide capable of catalyzing the conversion of acetyl-CoA and an alcohol to form CoA and an acetic ester. Additionally, one of ordinary skill in the art will appreciate that alcohol O-acetyltransferase peptides will catalyze other reactions as well, for example some alcohol O-acetyltransferase peptides will accept other substrates in addition to fatty alcohols or acetyl-CoA thiosester i.e such as other alcohols and other acyl-CoA thioesters. Such non-specific or divergent specificity alcohol O-acetyltransferase peptides are, therefore, also included. Alcohol O-acetyltransferase peptide sequences are publicly available. Exemplary GenBank Accession Numbers are provided in FIG. 10. Assays for characterizing the activity of a particular alcohol O-acetyltransferase peptides are well known in the art. Engineered O-acetyltransferases and O-acyltransferases can be also created that have new activities and specificities for the donor acyl group or acceptor alcohol moiety. Engineered enzymes could be generated through rational and evolutionary approaches well documented in the art.
F. Acyl-CoA to Fatty Esters (Bbiodiesels and Waxes)
Production hosts can be engineered using known peptides to produce fatty acid esters from acyl-CoA and alcohols. In some examples the alcohols are provided in the fermentation media and in other examples the production host can provide the alcohol as described herein. One of ordinary skill in the art will appreciate that structurally, fatty acid esters have an A and a B side. As described herein, the A side of the ester is used to describe the carbon chain contributed by the alcohol, and the B side of the ester is used to describe the carbon chain contributed by the acyl-CoA. Either chain can be saturated or unsaturated, branched or unbranched. The production host can be engineered to produce fatty alcohols or short chain alcohols. The production host can also be engineered to produce specific acyl-CoA molecules. As used herein fatty acid esters are esters derived from a fatty acyl-thioester and an alcohol, wherein the A side and the B side of the ester can vary in length independently. Generally, the A side of the ester is at least 1, 2, 3, 4, 5, 6, 7, or 8 carbons in length, while the B side of the ester is 8, 10, 12, 14, 16, 18, 20, 22, 24, or 26 carbons in length. The A side and the B side can be straight chain or branched, saturated or unsaturated.
The production of fatty esters, including waxes from acyl-CoA and alcohols can be engineered using known polypeptides. As used herein waxes are long chain fatty acid esters, wherein the A side and the B side of the ester can vary in length independently. Generally, the A side of the ester is at least 8, 10, 12, 14, 16, 18, 20, 22, 24, or 26 carbons in length. Similarly the B side of the ester is at least 8, 10, 12, 14, 16, 18, 20, 22, 24, or 26 carbons in length. The A side and the B side can be mono-, di-, tri-unsaturated. The production of fatty esters, including waxes from acyl-CoA and alcohols can be engineered using known polypeptides. One method of making fatty esters includes increasing the expression of or expressing more active forms of one or more wax synthases (EC 126.96.36.199).
As used herein, wax synthases includes peptides in enzyme classification number EC 188.8.131.52, as well as any other peptide capable of catalyzing the conversion of an acyl-thioester to fatty esters. Additionally, one of ordinary skill in the art will appreciate that some wax synthase peptides will catalyze other reactions as well, for example some wax synthase peptides will accept short chain acyl-CoAs and short chain alcohols to produce fatty esters. Such non-specific wax synthases are, therefore, also included. Wax synthase peptide sequences are publicly available. Exemplary GenBank Accession Numbers are provided in FIG. 10. Methods to identify wax synthase activity are provided in U.S. Pat. No. 7,118,896, which is herein incorporated by reference.
In particular examples, if the desired product is a fatty ester based biofuel, the microorganism is modified so that it produces a fatty ester generated from a renewable energy source. Such a microorganism includes an exongenous DNA sequence encoding a wax ester synthase that is expressed so as to confer upon said microorganism the ability to synthesize a saturated, unsaturated, or branched fatty ester from a renewable energy source. In some embodiments, the wax ester synthesis proteins include, but are not limited to,: fatty acid elongases, acyl-CoA reductases, acyltransferases or wax synthases, fatty acyl transferases, diacylglycerol acyltransferases, acyl-coA wax alcohol acyltransferases, bifunctional wax ester synthase/acyl-CoA:diacylglycerol acyltransferase selected from a multienzyme complex from Simmondsia chinensis, Acinetobacter sp. strain ADP 1 (formerly Acinetobacter calcoaceticus ADP1), Pseudomonas aeruginosa, Fundibacter jadensis, Arabidopsis thaliana, or Alkaligenes eutrophus. In one embodiment, the fatty acid elongases, acyl-CoA reductases or wax synthases are from a multienzyme complex from Alkaligenes eutrophus and other organisms known in the literature to produce wax and fatty acid esters.
Additional sources of heterologous DNA encoding wax synthesis proteins useful in fatty ester production include, but are not limited to, Mortierella alpina (for example ATCC 32222), Crytococcus curvatus, (also referred to as Apiotricum curvatum), Alcanivorax jadensis (for example T9T=DSM 12718=ATCC 700854), Acinetobacter sp. HO1-N, (for example ATCC 14987) and Rhodococcus opacus (for example PD630, DSMZ 44193).
The methods of described herein permit production of fatty esters of varied length. In one example, the fatty ester product is a saturated or unsaturated fatty ester product having a carbon atom content between 24 and 46 carbon atoms. In one embodiment, the fatty ester product has a carbon atom content between 24 and 32 carbon atoms. In another embodiment the fatty ester product has a carbon content of 14 and 20 carbons. In another embodiment the fatty ester is the methyl ester of C18:1. In another embodiment the fatty acid ester is the ethyl ester of C16:1. In another embodiment the fatty ester is the methyl ester of C16:1. In another embodiment the fatty acid ester is octadecyl ester of octanol.
Useful hosts for producing fatty esters can be either eukaryotic or prokaryotic microorganisms. In some embodiments such hosts include, but are not limited to, Saccharomyces cerevisiae, Candida lipolytica, E. coli Arthrobacter AK 19, Rhodotorula glutinins, Acinobacter sp strain M-1, Candida lipolytica and other oleaginous microorganisms.
In one example the wax ester synthase from Acinetobacter sp. ADP1 at locus AAO17391 (described in Kalscheuer and Steinbuchel, J. Biol. Chem. 278:8075-8082, 2003, herein incorporated by reference) is used. In another example the wax ester synthase from Simmondsia chinensis, at locus AAD38041 is used.
Optionally a wax ester exporter such as a member of the FATP family can be used to facilitate the release of waxes or esters into the extracellular environment. One example of a wax ester exporter that can be used is fatty acid (long chain) transport protein CG7400-PA, isoform A from Drosophila melanogaster, at locus NP--524723.
G. Acyl-ACP, Acyl-CoA to Hydrocarbon
A diversity of microorganisms are known to produce hydrocarbons, such as alkanes, olefins, and isoprenoids. Many of these hydrocarbons are derived from fatty acid biosynthesis. The production of these hydrocarbons can be controlled by controlling the genes associated with fatty acid biosynthesis in the native hosts. For example, hydrocarbon biosynthesis in the algae Botryococcus braunii occurs through the decarbonylation of fatty aldehydes. The fatty aldehydes are produced by the reduction of fatty acyl--thioesters by fatty acyl-CoA reductase. Thus, the structure of the final alkanes can be controlled by engineering B. braunii to express specific genes, such as thioesterases, which control the chain length of the fatty acids being channeled into alkane biosynthesis. Expressing the enzymes that result in branched chain fatty acid biosynthesis in B. braunii will result in the production of branched chain alkanes. Introduction of genes effecting the production of desaturation of fatty acids will result in the production of olefins. Further combinations of these genes can provide further control over the final structure of the hydrocarbons produced. To produce higher levels of the native or engineered hydrocarbons, the genes involved in the biosynthesis of fatty acids and their precursors or the degradation to other products can be expressed, overexpressed, or attenuated. Each of these approaches can be applied to the production of alkanes in Vibrio furnissi M1 and its functional homologues, which produces alkanes through the reduction of fatty alcohols (see above for the biosynthesis and engineering of fatty alcohol production). Each of these approaches can also be applied to the production of the olefins produced by many strains of Micrococcus leuteus, Stenotrophomonas maltophilia, Jeogalicoccus sp. (ATCC8456), and related microorganisms. These microorganisms produce long chain internal olefins that are derived from the head to head condensation of fatty acid precursors. Controlling the structure and level of the fatty acid precursors using the methods described herein will result in formation of olefins of different chain length, branching, and level of saturation.
Hydrocarbons can also be produced using evolved oxido/reductases for the reduction of primary alcohols. Primary fatty alcohols are known to be used to produce alkanes in microorganisms such as Vibrio furnissii M1 (Myong-Ok, J. Bacterial., 187:1426-1429, 2005). An NAD(P)H dependent oxido/reductase is the responsible catalyst. Synthetic NAD(P)H dependent oxidoreductases can be produced through the use of evolutionary engineering and be expressed in production hosts to produce fatty acid derivatives. One of ordinary skill in the art will appreciate that the process of "evolving" a fatty alcohol reductase to have the desired activity is well known (Kolkman and Stemmer Nat Biotechnol. 19:423-8, 2001, Ness et al., Adv Protein Chem. 55:261-92, 2000, Minshull and Stemmer Curr Opin Chem Biol. 3:284-90, 1999, Huisman and Gray Curr Opin Biotechnol. August; 13:352-8, 2002, and see U.S. patent application 2006/0195947). A library of NAD(P)H dependent oxidoreductases is generated by standard methods, such as error prone PCR, site-specific random mutagenesis, site specific saturation mutagenesis, or site directed specific mutagenesis. Additionally, a library can be created through the "shuffling" of naturally occurring NAD(P)H dependent oxidoreductase encoding sequences. The library is expressed in a suitable host, such as E. coli. Individual colonies expressing a different member of the oxido/reductase library is then analyzed for its expression of an oxido/reductase that can catalyze the reduction of a fatty alcohol. For example, each cell can be assayed as a whole cell bioconversion, a cell extract, a permeabilized cell, or a purified enzyme. Fatty alcohol reductases are identified by the monitoring the fatty alcohol dependent oxidation of NAD(P)H spectrophotometrically or fluorometrically. Production of alkanes is monitored by GC/MS, TLC, or other methods. An oxido/reductase identified in this manner is used to produce alkanes, alkenes, and related branched hydrocarbons. This is achieved either in vitro or in vivo. The later is achieved by expressing the evolved fatty alcohol reductase gene in an organism that produces fatty alcohols, such as those described herein. The fatty alcohols act as substrates for the alcohol reductase which would produce alkanes. Other oxidoreductases can be also engineered to catalyze this reaction, such as those that use molecular hydrogen, glutathione, FADH, or other reductive coenzymes.
II. Genetic Engineering of Production Strain to increase Fatty Acid Derivative Production
Heterologous DNA sequences involved in a biosynthetic pathway for the production of fatty acid derivatives can be introduced stably or transiently into a host cell using techniques well known in the art for example electroporation, calcium phosphate precipitation, DEAE-dextran mediated transfection, liposome-mediated transfection, conjugation, transduction, and the like. For stable transformation, a DNA sequence can further include a selectable marker, such as, antibiotic resistance, for example resistance to neomycin, tetracycline, chloramphenicol, kanamycin, genes that complement auxotrophic deficiencies, and the like.
Various embodiments of this disclosure utilize an expression vector that includes a heterologous DNA sequence encoding a protein involved in a metabolic or biosynthetic pathway. Suitable expression vectors include, but are not limited to, viral vectors, such as baculovirus vectors, phage vectors, such as bacteriophage vectors, plasmids, phagemids, cosmids, fosmids, bacterial artificial chromosomes, viral vectors (e.g. viral vectors based on vaccinia virus, poliovirus, adenovirus, adeno-associated virus, SV40, herpes simplex virus, and the like), P1-based artificial chromosomes, yeast plasmids, yeast artificial chromosomes, and any other vectors specific for specific hosts of interest (such as E. coli, Pseudomonas pisum and Saccharomyces cerevisiae).
Useful expression vectors can include one or more selectable marker genes to provide a phenotypic trait for selection of transformed host cells. The selectable marker gene encodes a protein necessary for the survival or growth of transformed host cells grown in a selective culture medium. Host cells not transformed with the vector containing the selectable marker gene will not survive in the culture medium. Typical selection genes encode proteins that (a) confer resistance to antibiotics or other toxins, e.g., ampicillin, neomycin, methotrexate, or tetracycline, (b) complement auxotrophic deficiencies, or (c) supply critical nutrients not available from complex media, e.g., the gene encoding D-alanine racemase for Bacilli. In alternative embodiments, the selectable marker gene is one that encodes dihydrofolate reductase or confers neomycin resistance (for use in eukaryotic cell culture), or one that confers tetracycline or ampicillin resistance (for use in a prokaryotic host cell, such as E. coli).
The biosynthetic pathway gene product-encoding DNA sequence in the expression vector is operably linked to an appropriate expression control sequence, (promoters, enhancers, and the like) to direct synthesis of the encoded gene product. Such promoters can be derived from microbial or viral sources, including CMV and SV40. Depending on the host/vector system utilized, any of a number of suitable transcription and translation control elements, including constitutive and inducible promoters, transcription enhancer elements, transcription terminators, etc. can be used in the expression vector (see e.g., Bitter et al., Methods in Enzymology, 153:516-544, 1987).
Suitable promoters for use in prokaryotic host cells include, but are not limited to, promoters capable of recognizing the T4, T3, Sp6 and T7 polymerases, the PR and PL promoters of bacteriophage lambda, the trp, recA, heat shock, and lacZ promoters of E. coli, the alpha-amylase and the sigma-specific promoters of B. subtilis, the promoters of the bacteriophages of Bacillus, Streptomyces promoters, the int promoter of bacteriophage lambda, the bla promoter of the beta-lactamase gene of pBR322, and the CAT promoter of the chloramphenicol acetyl transferase gene. Prokaryotic promoters are reviewed by Glick, J. Ind. Microbiol. 1:277, 1987; Watson et al., MOLECULAR BIOLOGY OF THE GENE, 4th Ed., Benjamin Cummins (1987); and Sambrook et al., supra.
Non-limiting examples of suitable eukaryotic promoters for use within a eukaryotic host are viral in origin and include the promoter of the mouse metallothionein I gene (Hamer et al., J. Mol. Appl. Gen. 1:273, 1982); the TK promoter of Herpes virus (McKnight, Cell 31:355, 1982); the SV40 early promoter (Benoist et al., Nature (London) 290:304, 1981); the Rous sarcoma virus promoter; the cytomegalovirus promoter (Foecking et al., Gene 45:101, 1980); the yeast gal4 gene promoter (Johnston, et al., PNAS (USA) 79:6971, 1982; Silver, et al., PNAS (USA) 81:5951, 1984); and the IgG promoter (Orlandi et al., PNAS (USA) 86:3833, 1989).
The microbial host cell can be genetically modified with a heterologous DNA sequence encoding a biosynthetic pathway gene product that is operably linked to an inducible promoter. Inducible promoters are well known in the art. Suitable inducible promoters include, but are not limited to promoters that are affected by proteins, metabolites, or chemicals. These include: a bovine leukemia virus promoter, a metallothionein promoter, a dexamethasone-inducible MMTV promoter, a SV40 promoter, a MRP polIII promoter, a tetracycline-inducible CMV promoter (such as the human immediate-early CMV promoter) as well as those from the trp and lac operons.
In some examples a genetically modified host cell is genetically modified with a heterologous DNA sequence encoding a biosynthetic pathway gene product that is operably linked to a constitutive promoter. Suitable constitutive promoters are known in the art and include, constitutive adenovirus major late promoter, a constitutive MPSV promoter, and a constitutive CMV promoter.
In some examples a modified host cell is one that is genetically modified with an exongenous DNA sequence encoding a single protein involved in a biosynthesis pathway. In other embodiments, a modified host cell is one that is genetically modified with exongenous DNA sequences encoding two or more proteins involved in a biosynthesis pathway--for example, the first and second enzymes in a biosynthetic pathway.
Where the host cell is genetically modified to express two or more proteins involved in a biosynthetic pathway, those DNA sequences can each be contained in a single or in separate expression vectors. When those DNA sequences are contained in a single expression vector, in some embodiments, the nucleotide sequences will be operably linked to a common control element (e.g., a promoter), e.g., the common control element controls expression of all of the biosynthetic pathway protein-encoding DNA sequences in the single expression vector.
When a modified host cell is genetically modified with heterologous DNA sequences encoding two or more proteins involved in a biosynthesis pathway, one of the DNA sequences can be operably linked to an inducible promoter, and one or more of the DNA sequences can be operably linked to a constitutive promoter.
In some embodiments, the intracellular concentration (e.g., the concentration of the intermediate in the genetically modified host cell) of the biosynthetic pathway intermediate can be increased to further boost the yield of the final product. The intracellular concentration of the intermediate can be increased in a number of ways, including, but not limited to, increasing the concentration in the culture medium of a substrate for a biosynthetic pathway; increasing the catalytic activity of an enzyme that is active in the biosynthetic pathway; increasing the intracellular amount of a substrate (e.g., a primary substrate) for an enzyme that is active in the biosynthetic pathway; and the like.
In some examples the fatty acid derivative or intermediate is produced in the cytoplasm of the cell. The cytoplasmic concentration can be increased in a number of ways, including, but not limited to, binding of the fatty acid to coenzyme A to form an acyl-CoA thioester. Additionally, the concentration of acyl-CoAs can be increased by increasing the biosynthesis of CoA in the cell, such as by over-expressing genes associated with pantothenate biosynthesis (panD) or knocking out the genes associated with glutathione biosynthesis (glutathione synthase).
III. Carbon Chain Characteristics
Using the teachings provided herein a range of products can be produced. These products include hydrocarbons, fatty alcohols, fatty acid esters, and waxes. Some of these products are useful as biofuels and specialty chemicals. These products can be designed and produced in microorganisms. The products can be produced such that they contain branch points, levels of saturation, and carbon chain length, thus, making these products desirable starting materials for use in many applications (FIG. 10 provides a description of the various enzymes that can be used alone or in combination to make various fatty acid derivatives).
In other examples, the expression of exongenous FAS genes originating from different species or engineered variants can be introduced into the host cell to result in the biosynthesis of fatty acid metabolites structurally different (in length, branching, degree of unsaturation, etc.) as that of the native host. These heterologous gene products can be also chosen or engineered so that they are unaffected by the natural complex regulatory mechanisms in the host cell and, therefore, function in a manner that is more controllable for the production of the desired commercial product. For example the FAS enzymes from Bacillus subtilis, Saccharomyces cerevisiae, Streptomyces spp, Ralstonia, Rhodococcus, Corynebacteria, Brevibacteria, Mycobacteria, oleaginous yeast, and the like can be expressed in the production host.
One of ordinary skill in the art will appreciate that when a production host is engineered to produce a fatty acid from the fatty acid biosynthetic pathway that contains a specific level of unsaturation, branching, or carbon chain length the resulting engineered fatty acid can be used in the production of the fatty acid derivatives. Hence, fatty acid derivatives generated from the production host can display the characteristics of the engineered fatty acid. For example, a production host can be engineered to make branched, short chain fatty acids, and then using the teachings provided herein relating to fatty alcohol production (i.e. including alcohol forming enzymes such as FAR) the production host produce branched, short chain fatty alcohols. Similarly, a hydrocarbon can be produced by engineering a production host to produce a fatty acid having a defined level of branching, unsaturation, and/or carbon chain length, thus, producing a homogenous hydrocarbon population. Moreover, when an unsaturated alcohol, fatty acid ester, or hydrocarbon is desired the fatty acid biosynthetic pathway can be engineered to produce low levels of saturated fatty acids and an additional desaturase can be expressed to lessen the saturated product production.
Production hosts can be engineered to produce unsaturated fatty acids by engineering the production host to over-express fabB, or by growing the production host at low temperatures (for example less than 37° C.). FabB has preference to cis-δ3decenoyl-ACP and results in unsaturated fatty acid production in E. coli. Over-expression of FabB resulted in the production of a significant percentage of unsaturated fatty acids (de Mendoza et al, J. Biol. Chem., 258:2098-101, 1983). These unsaturated fatty acids can then be used as intermediates in production hosts that are engineered to produce fatty acid derivatives, such as fatty alcohols, esters, waxes, olefins, alkanes, and the like. One of ordinary skill in the art will appreciate that by attenuating fabA, or over-expressing FabB and expressing specific thioesterases (described below), unsaturated fatty acid derivatives having a desired carbon chain length can be produced. Alternatively, the repressor of fatty acid biosynthesis, FabR (Genbank accession NP--418398), can be deleted, which will also result in increased unsaturated fatty acid production in E. coli (Zhang et al., J. Biol. Chem. 277:pp. 15558, 2002.). Further increase in unsaturated fatty acids may be achieved by over-expression of FabM (trans-2, cis-3-decenoyl-ACP isomerase, Genbank accession DAA05501) and controlled expression of FabK (trans-2-enoyl-ACP reductase II, Genbank accession NP--357969) from Streptococcus pneumoniae (Marrakchi et al., J. Biol. Chem. 277: 44809, 2002), while deleting E. coli Fab I ((trans-2-enoyl-ACP reductase, Genbank accession NP--415804). Additionally, to increase the percentage of unsaturated fatty acid esters, the microorganism can also have fabB (encoding γ-ketoacyl-ACP synthase I, Accessions: BAA16180, EC:184.108.40.206), Sfa (encoding a suppressor of fabA, Accession: AAC44390) and gnsA and gnsB (both encoding secG null mutant suppressors, a.k.a. cold shock proteins, Accession: ABD18647.1, AAC74076.1) over-expressed.
In some examples, the endogenous fabF gene can be attenuated, thus, increasing the percentage of palmitoleate (C 16:1) produced.
B. Branching Including Cyclic Moieties
Fatty acid derivatives can be produced that contain branch points, cyclic moieties, and combinations thereof, using the teachings provided herein.
Microorganisms that naturally produce straight fatty acids (sFAs) can be engineered to produce branched chain fatty acids (brFAs) by expressing one or more exogenous nucleic acid sequences. For example, E. coli naturally produces straight fatty acids (sFAs). To engineer E. coli to produce brFAs, several genes can be introduced and expressed that provide branched precursors (bkd operon) and allow initiation of fatty acid biosynthesis from branched precursors (fabH). Additionally, the organism can express genes for the elongation of brFAs (e.g. ACP, FabF) and/or deleting the corresponding E. coli genes that normally lead to sFAs and would compete with the introduced genes (e.g. FabH, FabF).
The branched acyl-CoAs 2-methyl-buturyl-CoA, isovaleryl-CoA and isobuturyl-CoA are the precursors of brFA. In most brFA-containing microorganisms they are synthesized in two steps (described in detail below) from branched amino acids (isoleucine, leucine and valine) (Kadena, Microbiol. Rev. 55: pp. 288, 1991). To engineer a microorganism to produce brFAs, or to overproduce brFAs, expression or over-expression of one or more of the enzymes in these two steps can be engineered. For example, in some instances the production host may have an endogenous enzyme that can accomplish one step and therefore, only enzymes involved in the second step need to be expressed recombinantly.
The first step in forming branched fatty acids is the production of the corresponding α-keto acids by a branched-chain amino acid aminotransferase. E. coli has such an enzyme, IlvE (EC 220.127.116.11; Genbank accession YP--026247). In some examples, a heterologous branched-chain amino acid aminotransferase may not be expressed. However, E. coli IlvE or any other branched-chain amino acid aminotransferase, e.g. ilvE from Lactococcus lactis (Genbank accession AAF34406), ilvE from Pseudomonas putida (Genbank accession NP--745648) or ilvE from Streptomyces coelicolor (Genbank accession NP--629657) can be over-expressed in a host microorganism, should the aminotransferase reaction turn out to be rate limiting in brFA biosynthesis in the host organism chosen for fatty acid derivative production.
The second step, the oxidative decarboxylation of the α-ketoacids to the corresponding branched-chain acyl-CoA, is catalyzed by a branched-chain α-keto acid dehydrogenase complexes (bkd; EC 18.104.22.168.) (Denoya et al. J. Bacteria 177:pp. 3504, 1995), which consist of E1α/β (decarboxylase), E2 (dihydrolipoyl transacylase) and E3 (dihydrolipoyl dehydrogenase) subunits and are similar to pyruvate and α-ketoglutarate dehydrogenase complexes. Table 2 shows potential bkd genes from several microorganisms, that can be expressed in a production host to provide branched-chain acyl-CoA precursors. Basically, every microorganism that possesses brFAs and/or grows on branched-chain amino acids can be used as a source to isolate bkd genes for expression in production hosts such as, for example, E. coli. Furthermore, E. coli has the E3 component (as part of its pyruvate dehydrogenase complex; 1pd, EC 22.214.171.124, Genbank accession NP--414658), it can therefore, be sufficient to only express the E1 /β and E2 bkd genes.
TABLE-US-00002 TABLE 2 Bkd genes from selected microorganisms Organism Gene Genbank Accession # Streptomyces coelicolor bkdA1 (E1α) NP_628006 bkdB1 (E1β) NP_628005 bkdC1 (E2) NP_638004 Streptomyces coelicolor bkdA2 (E1α) NP_733618 bkdB2 (E1β) NP_628019 bkdC2 (E2) NP_628018 Streptomyces avermitilis bkdA (E1a) BAC72074 bkdB (E1b) BAC72075 bkdC (E2) BAC72076 Streptomyces avermitilis bkdF (E1α) BAC72088 bkdG (E1β) BAC72089 bkdH (E2) BAC72090 Bacillus subtilis bkdAA (E1α) NP_390288 bkdAB (E1β) NP_390288 bkdB (E2) NP_390288 Pseudomonas putida bkdA1 (E1α) AAA65614 bkdA2 (E1β) AAA65615 bkdC (E2) AAA65617
In another example, isobuturyl-CoA can be made in a production host, for example in E. coli through the coexpression of a crotonyl-CoA reductase (Ccr, EC 126.96.36.199) and isobuturyl-CoA mutase (large subunit IcmA, EC 188.8.131.52; small subunit IcmB, EC 184.108.40.206) (Han and Reynolds J. Bacteriol. 179:pp. 5157, 1997). Crotonyl-CoA is an intermediate in fatty acid biosynthesis in E. coli and other microorganisms. Examples for ccr and icm genes from selected microorganisms are given in Table 3.
TABLE-US-00003 TABLE 3 Ccr and icm genes from selected microorganisms Organism Gene Genbank Accession # Streptomyces coelicolor ccr NP_630556 icmA NP_629554 icmB NP_630904 Streptomyces cinnamonensis ccr AAD53915 icmA AAC08713 icmB AJ246005
In addition to expression of the bkd genes (see above), the initiation of brFA biosynthesis utilizes β-ketoacyl-acyl-carrier-protein synthase III (FabH, EC 220.127.116.11) with specificity for branched chain acyl CoAs (Li et al. J. Bacteriol. 187:pp. 3795, 2005). Examples of such FabHs are listed in Table 4. FabH genes that are involved in fatty acid biosynthesis of any brFA-containing microorganism can be expressed in a production host. The Bkd and FabH enzymes from production hosts that do not naturally make brFA may not support brFA production and therefore, Bkd and FabH can be expressed recombinantly. Similarly, the endogenous level of Bkd and FabH production may not be sufficient to produce brFA, therefore, they can be over-expressed. Additionally, other components of fatty acid biosynthesis machinery can be expressed such as acyl carrier proteins (ACPs) and β-ketoacyl-acyl-carrier-protein synthase II candidates are acyl carrier proteins (ACPs) and β-ketoacyl-acyl-carrier-protein synthase II (fabF, EC 18.104.22.168) (candidates are listed in Table 4). In addition to expressing these genes, some genes in the endogenous fatty acid biosynthesis pathway may be attenuated in the production host. For example, in E. coli the most likely candidates to interfere with brFA biosynthesis are fabH (Genbank accession #NP--415609) and/or fabF genes (Genbank accession #NP--415613).
As mentioned above, through the combination of expressing genes that support brFA synthesis and alcohol synthesis branched chain alcohols can be produced. For example, when an alcohol reductase such as Acr1 from Acinetobacter baylyi ADP1 is coexpressed with a bkd operon, E. coli can synthesize isopentanol, isobutanol or 2-methyl butanol. Similarly, when Acr1 is coexpressed with ccr/icm genes, E. coli can synthesize isobutanol.
In order to convert a production host such as E. coli into an organism capable of synthesizing ω-cyclic fatty acids (cyFAs), several genes need to be introduced and expressed that provide the cyclic precursor cyclohexylcarbonyl-CoA (Cropp et al. Nature Biotech. 18:pp. 980, 2000). The genes listed in Table 4 (fabH, ACP and fabF) can then be expressed to allow initiation and elongation of ω-cyclic fatty acids. Alternatively, the homologous genes can be isolated from microorganisms that make cyFAs and expressed in E. coli.
TABLE-US-00004 TABLE 4 FabH, ACP and fabF genes from selected microorganisms with brFAs Genbank Organism Gene Accession # Streptomyces coelicolor fabH1 NP_626634 ACP NP_626635 fabF NP_626636 Streptomyces avermitilis fabH3 NP_823466 fabC3 (ACP) NP_823467 fabF NP_823468 Bacillus subtilis fabH_A NP_389015 fabH_B NP_388898 ACP NP_389474 fabF NP_389016 Stenotrophomonas maltophilia SmalDRAFT_0818 ZP_01643059 (FabH) SmalDRAFT_0821 ZP_01643063 (ACP) SmalDRAFT_0822 ZP_01643064 (FabF) Legionella pneumophila FabH YP_123672 ACP YP_123675 fabF YP_123676
Expression of the following genes are sufficient to provide cyclohexylcarbonyl-CoA in E. coli: ansJ, ansK, ansL, chcA and ansM from the ansatrienin gene cluster of Streptomyces collinus (Chen et al., Eur. J. Biochem. 261:pp. 1999, 1999) or plmJ, plmK, plmL, chcA and plmM from the phoslactomycin B gene cluster of Streptomyces sp. HK803 (Palaniappan et al., J. Biol. Chem. 278:pp. 35552, 2003) together with the chcB gene (Patton et al. Biochem., 39:pp. 7595, 2000) from S. collinus, S. avermitilis or S. coelicolor (see Table 5 for Genbank accession numbers).
TABLE-US-00005 TABLE 5 Genes for the synthesis of cyclohexylcarbonyl-CoA Organism Gene Genbank Accession # Streptomyces collinus ansJK U72144* ansL chcA ansL chcB AF268489 Streptomyces sp. HK803 pmlJK AAQ84158 pmlL AAQ84159 chcA AAQ84160 pmlM AAQ84161 Streptomyces coelicolor chcB/caiD NP_629292 Streptomyces avermitilis chcB/caiD NP_629292 Only chcA is annotated in Genbank entry U72144, ansJKLM are according to Chen et al. (Eur. J. Biochem. 261: pp. 1999, 1999)
The genes listed in Table 4 (fabH, ACP and fabF) are sufficient to allow initiation and elongation of ω-cyclic fatty acids, because they can have broad substrate specificity. In the event that coexpression of any of these genes with the ansJKLM/chcAB or pm1JKLM/chcAB genes from Table 5 does not yield cyFAs, fabH, ACP and/or fabF homologs from microorganisms that make cyFAs can be isolated (e.g. by using degenerate PCR primers or heterologous DNA probes) and coexpressed. Table 6 lists selected microorganisms that contain ω-cyclic fatty acids.
TABLE-US-00006 TABLE 6 Examples of microorganisms that contain ω-cyclic fatty acids Organism Reference Curtobacterium pusillum ATCC19096 Alicyclobacillus acidoterrestris ATCC49025 Alicyclobacillus acidocaldarius ATCC27009 Alicyclobacillus cycloheptanicum* Moore, J. Org. Chem. 62: pp. 2173, 1997. *uses cycloheptylcarbonyl-CoA and not cyclohexylcarbonyl-CoA as precursor for cyFA biosynthesis
C. Ester Characteristics
One of ordinary skill in the art will appreciate that an ester includes an A side and a B side. As described herein, the B side is contributed by a fatty acid produced from de novo synthesis in the host organism. In some instances where the host is additionally engineered to make alcohols, including fatty alcohols, the A side is also produced by the host organism. In yet other examples the A side can be provided in the medium. As described herein, by selecting the desired thioesterase genes the B side, and when fatty alcohols are being made the A side, can be designed to be have certain carbon chain characteristics. These characteristics include points of unsaturation, branching, and desired carbon chain lengths. Exemplary methods of making long chain fatty acid esters, wherein the A and B side are produced by the production host are provided in Example 6, below. Similarly, Example 5 provides methods of making medium chain fatty acid esters. When both the A and B side are contributed by the production host and they are produced using fatty acid biosynthetic pathway intermediates they will have similar carbon chain characteristics. For example, at least 50%, 60%, 70%, or 80% of the fatty acid esters produced will have A sides and B sides that vary by 6, 4, or 2 carbons in length. The A side and the B side will also display similar branching and saturation levels.
In addition to producing fatty alcohols for contribution to the A side, the host can produce other short chain alcohols such as ethanol, propanol, isopropanol, isobutanol, and butanol for incorporation on the A side using techniques well known in the art. For example, butanol can be made by the host organism. To create butanol producing cells, the LS9001 strain (described in Example 1, below) can be further engineered to express atoB (acetyl-CoA acetyltransferase) from Escherichia coli K12, β-hydroxybutyryl-CoA dehydrogenase from Butyrivibrio fibrisolvens, crotonase from Clostridium beijerinckii, butyryl CoA dehydrogenase from Clostridium beijerinckii, CoA-acylating aldehyde dehydrogenase (ALDH) from Cladosporium fulvum, and adhE encoding an aldehyde-alchol dehydrogenase of Clostridium acetobutylicum in the pBAD24 expression vector under the prpBCDE promoter system. Similarly, ethanol can be produced in a production host using the methods taught by Kalscheuer et al., Microbiology 152:2529-2536, 2006, which is herein incorporated by reference.
The production and isolation of fatty acid derivatives can be enhanced by employing specific fermentation techniques. One method for maximizing production while reducing costs is increasing the percentage of the carbon source that is converted to hydrocarbon products. During normal cellular lifecycles carbon is used in cellular functions including producing lipids, saccharides, proteins, organic acids, and nucleic acids. Reducing the amount of carbon necessary for growth-related activities can increase the efficiency of carbon source conversion to output. This can be achieved by first growing microorganisms to a desired density, such as a density achieved at the peak of the log phase of growth. At such a point, replication checkpoint genes can be harnessed to stop the growth of cells. Specifically, quorum sensing mechanisms (reviewed in Camilli and Bassler Science 311:1113, 2006; Venturi FEMS Microbio Rev 30:274-291, 2006; and Reading and Sperandio FEMS Microbiol Lett 254:1-11, 2006) can be used to activate genes such as p53, p21, or other checkpoint genes. Genes that can be activated to stop cell replication and growth in E. coli include umuDC genes, the over-expression of which stops the progression from stationary phase to exponential growth (Murli et al., J. of Bact. 182:1127, 2000). UmuC is a DNA polymerase that can carry out translesion synthesis over non-coding lesions--the mechanistic basis of most UV and chemical mutagenesis. The umuDC gene products are used for the process of translesion synthesis and also serve as a DNA damage checkpoint. UmuDC gene products include UmuC, UmuD, umuD', UmuD'2C, UmuD'2 and UmuD2. Simultaneously, the product producing genes would be activated, thus minimizing the need for replication and maintenance pathways to be used while the fatty acid derivative is being made.
The percentage of input carbons converted to hydrocarbon products is a cost driver. The more efficient (i.e. the higher the percentage), the less expensive the process. For oxygen-containing carbon sources (i.e. glucose and other carbohydrate based sources), the oxygen must be released in the form of carbon dioxide. For every 2 oxygen atoms released, a carbon atom is also released leading to a maximal theoretical metabolic efficiency of ˜34% (w/w) (for fatty acid derived products). This figure, however, changes for other hydrocarbon products and carbon sources. Typical efficiencies in the literature are ˜<5%. Engineered microorganisms which produce hydrocarbon products can have greater than 1, 3, 5, 10, 15, 20, 25, and 30% efficiency. In one example microorganisms will exhibit an efficiency of about 10% to about 25%. In other examples, such microorganisms will exhibit an efficiency of about 25% to about 30%, and in other examples such microorganisms will exhibit >30% efficiency.
In some examples where the final product is released from the cell, a continuous process can be employed. In this approach, a reactor with organisms producing fatty acid derivatives can be assembled in multiple ways. In one example, a portion of the media is removed and let to sit. Fatty acid derivatives are separated from the aqueous layer, which will in turn, be returned to the fermentation chamber.
In one example, the fermentation chamber will enclose a fermentation that is undergoing a continuous reduction. In this instance, a stable reductive environment would be created. The electron balance would be maintained by the release of carbon dioxide (in gaseous form). Efforts to augment the NAD/H and NADP/H balance can also facilitate in stabilizing the electron balance.
The availability of intracellular NADPH can be also enhanced by engineering the production host to express an NADH:NADPH transhydrogenase. The expression of one or more NADH:NADPH transhydrogenase converts the NADH produced in glycolysis to NADPH which enhances the production of fatty acid derivatives.
Disclosed herein is a system for continuously producing and exporting fatty acid derivatives out of recombinant host microorganisms via a transport protein. Many transport and efflux proteins serve to excrete a large variety of compounds and can be evolved to be selective for a particular type of fatty acid derivatives. Thus, in some embodiments an exogenous DNA sequence encoding an ABC transporter will be functionally expressed by the recombinant host microorganism, so that the microorganism exports the fatty acid derivative into the culture medium. In one example, the ABC transporter is an ABC transporter from Caenorhabditis elegans, Arabidopsis thalania, Alkaligenes eutrophus or Rhodococcus erythropolis (locus AAN73268). In another example, the ABC transporter is an ABC transporter chosen from CER5 (locuses At1g51500 or AY734542), AtMRP5, AmiS2 and AtPGP1. In some examples, the ABC transporter is CER5. In yet another example, the CER5 gene is from Arabidopsis (locuses At1g51500, AY734542, At3g21090 and At1g51460).
The transport protein, for example, can also be an efflux protein selected from: AcrAB, TolC and AcrEF from E. coli, or tll1618, tll1619 and tll0139 from Thermosynechococcus elongatus BP-1.
In addition, the transport protein can be, for example, a fatty acid transport protein (FATP) selected from Drosophila melanogaster, Caenorhabditis elegans, Mycobacterium tuberculosis or Saccharomyces cerevisiae or any one of the mammalian FATP's. The FATPs can additionally be resynthesized with the membranous regions reversed in order to invert the direction of substrate flow. Specifically, the sequences of amino acids composing the hydrophilic domains (or membrane domains) of the protein, could be inverted while maintaining the same codons for each particular amino acid. The identification of these regions is well known in the art.
Production hosts can also be chosen for their endogenous ability to release fatty acid derivatives. The efficiency of product production and release into the fermentation broth can be expressed as a ratio intracellular product to extracellular product. In some examples the ratio can be 5:1, 4:1, 3:1, 2:1, 1:1, 1:2, 1:3, 1:4, or 1:5.
The production host can be additionally engineered to express recombinant cellulosomes, such as those described in PCT application number PCT/US2007/003736, which will allow the production host to use cellulosic material as a carbon source. For example, the production host can be additionally engineered to express invertases (EC 22.214.171.124) so that sucrose can be used as a carbon source.
Similarly, the production host can be engineered using the teachings described in U.S. Pat. Nos. 5,000,000, 5,028,539, 5,424,202, 5,482,846, and 5,602,030 to Ingram et al. so that the production host can assimilate carbon efficiently and use cellulosic materials as carbons sources.
IV. Post Production Processing
The fatty acid derivatives produced during fermentation can be separated from the fermentation media. Any technique known for separating fatty acid derivatives from aqueous media can be used. One exemplary separation process provided herein is a two phase (bi-phasic) separation process. This process involves fermenting the genetically engineered production hosts under conditions sufficient to produce a fatty acid derivative, allowing the derivative to collect in an organic phase and separating the organic phase from the aqueous fermentation broth. This method can be practiced in both a batch and continuous fermentation setting.
Bi-phasic separation uses the relative immisiciblity of fatty acid derivatives to facilitate separation. Immiscible refers to the relative inability of a compound to dissolve in water and is defined by the compounds partition coefficient. The partition coefficient, P, is defined as the equilibrium concentration of compound in an organic phase (in a bi-phasic system the organic phase is usually the phase formed by the fatty acid derivative during the production process, however, in some examples an organic phase can be provided (such as a layer of octane to facilitate product separation) divided by the concentration at equilibrium in an aqueous phase (i.e. fermentation broth). When describing a two phase system the P is usually discussed in terms of logP. A compound with a logP of 10 would partition 10:1 to the organic phase, while a compound of logP of 0.1 would partition 10:1 to the aqueous phase. One or ordinary skill in the art will appreciate that by choosing a fermentation broth and the organic phase such that the fatty acid derivative being produced has a high logP value, the fatty acid derivative will separate into the organic phase, even at very low concentrations in the fermentation vessel.
The fatty acid derivatives produced by the methods described herein will be relatively immiscible in the fermentation broth, as well as in the cytoplasm. Therefore, the fatty acid derivative will collect in an organic phase either intracellularly or extracellularly. The collection of the products in an organic phase will lessen the impact of the fatty acid derivative on cellular function and will allow the production host to produce more product. Stated another way, the concentration of the fatty acid derivative will not have as significant of an impact on the host cell.
The fatty alcohols, fatty acid esters, waxes, and hydrocarbons produced as described herein allow for the production of homogeneous compounds wherein at least 60%, 70%, 80%, 90%, or 95% of the fatty alcohols, fatty acid esters, and waxes produced will have carbon chain lengths that vary by less than 4 carbons, or less than 2 carbons. These compounds can also be produced so that they have a relatively uniform degree of saturation, for example at least 60%, 70%, 80%, 90%, or 95% of the fatty alcohols, fatty acid esters, hydrocarbons and waxes will be mono-, di-, or tri-unsaturated. These compounds can be used directly as fuels, personal care additives, nutritional supplements. These compounds can also be used as feedstock for subsequent reactions for example transesterification, hydrogenation, catalytic cracking via either hydrogenation, pyrolisis, or both or epoxidations reactions to make other products.
V. Fuel Compositions
The fatty acid derivatives described herein can be used as fuel. One of ordinary skill in the art will appreciate that depending upon the intended purpose of the fuel different fatty acid derivatives can be produced and used. For example, for automobile fuel that is intended to be used in cold climates a branched fatty acid derivative may be desirable and using the teachings provided herein, branched hydrocarbons, fatty acid esters, and alcohols can be made. Using the methods described herein fuels comprising relatively homogeneous fatty acid derivatives that have desired fuel qualities can be produced. Such fuels can be characterized by carbon fingerprinting, their lack of impurities when compared to petroleum derived fuels or bio-diesel derived from triglycerides and, moreover, the fatty acid derivative based fuels can be combined with other fuels or fuel additives to produce fuels having desired properties.
A. Carbon Fingerprinting
Biologically produced fatty acid derivatives represent a new feedstock for fuels, such as alcohols, diesel and gasoline. Some biofuels made using fatty acid derivatives have not been produced from renewable sources and as such, are new compositions of matter. These new fuels can be distinguished from fuels derived form petrochemical carbon on the basis of dual carbon-isotopic fingerprinting. Additionally, the specific source of biosourced carbon (e.g. glucose vs. glycerol) can be determined by dual carbon-isotopic fingerprinting (see, U.S. Pat. No. 7,169,588, which is herein incorporated by reference).
This method usefully distinguishes chemically-identical materials, and apportions carbon in products by source (and possibly year) of growth of the biospheric (plant) component. The isotopes, 14C and 13C, bring complementary information to this problem. The radiocarbon dating isotope (14C), with its nuclear half life of 5730 years, clearly allows one to apportion specimen carbon between fossil ("dead") and biospheric ("alive") feedstocks [Currie, L. A. "Source Apportionment of Atmospheric Particles," Characterization of Environmental Particles, J. Buffle and H. P. van Leeuwen, Eds., 1 of Vol. I of the IUPAC Environmental Analytical Chemistry Series (Lewis Publishers, Inc) (1992) 3 74]. The basic assumption in radiocarbon dating is that the constancy of 14C concentration in the atmosphere leads to the constancy of 14C in living organisms. When dealing with an isolated sample, the age of a sample can be deduced approximately by the relationship t=(-5730/0.693)ln(A/AO) (Equation 5) where t=age, 5730 years is the half-life of radiocarbon, and A and AO are the specific 14C activity of the sample and of the modem standard, respectively [Hsieh, Y., Soil Sci. Soc. Am J., 56, 460, (1992)]. However, because of atmospheric nuclear testing since 1950 and the burning of fossil fuel since 1850, 14C has acquired a second, geochemical time characteristic. Its concentration in atmospheric CO2--and hence in the living biosphere--approximately doubled at the peak of nuclear testing, in the mid-1960s. It has since been gradually returning to the steady-state cosmogenic (atmospheric) baseline isotope rate (14C /12C) of ca. 1.2×1012, with an approximate relaxation "half-life" of 7-10 years. (This latter half-life must not be taken literally; rather, one must use the detailed atmospheric nuclear input/decay function to trace the variation of atmospheric and biospheric 14C since the onset of the nuclear age.) It is this latter biospheric 14C time characteristic that holds out the promise of annual dating of recent biospheric carbon. 14C can be measured by accelerator mass spectrometry (AMS), with results given in units of "fraction of modern carbon" (fM). fM is defined by National Institute of Standards and Technology (NIST) Standard Reference Materials (SRMs) 4990B and 4990C, known as oxalic acids standards HOxI and HOxII, respectively. The fundamental definition relates to 0.95 times the 14C/12C isotope ratio HOxI (referenced to AD 1950). This is roughly equivalent to decay-corrected pre-Industrial Revolution wood. For the current living biosphere (plant material), fM approx 1.1.
The stable carbon isotope ratio (13C/12C) provides a complementary route to source discrimination and apportionment. The 13C/12C ratio in a given biosourced material is a consequence of the 13C/12C ratio in atmospheric carbon dioxide at the time the carbon dioxide is fixed and also reflects the precise metabolic pathway. Regional variations also occur. Petroleum, C3 plants (the broadleaf), C4 plants (the grasses), and marine carbonates all show significant differences in 13C/12C and the corresponding delta13C values. Furthermore, lipid matter of C3 and C4 plants analyze differently than materials derived from the carbohydrate components of the same plants as a consequence of the metabolic pathway. Within the precision of measurement, 13C shows large variations due to isotopic fractionation effects, the most significant of which for the instant invention is the photosynthetic mechanism. The major cause of differences in the carbon isotope ratio in plants is closely associated with differences in the pathway of photosynthetic carbon metabolism in the plants, particularly the reaction occurring during the primary carboxylation, i.e., the initial fixation of atmospheric CO2. Two large classes of vegetation are those that incorporate the "C3" (or Calvin-Benson) photosynthetic cycle and those that incorporate the "C4" (or Hatch-Slack) photosynthetic cycle. C3 plants, such as hardwoods and conifers, are dominant in the temperate climate zones. In C3 plants, the primary CO2 fixation or carboxylation reaction involves the enzyme ribulose-1,5-diphosphate carboxylase and the first stable product is a 3-carbon compound. C4 plants, on the other hand, include such plants as tropical grasses, corn and sugar cane. In C4 plants, an additional carboxylation reaction involving another enzyme, phosphoenol-pyruvate carboxylase, is the primary carboxylation reaction. The first stable carbon compound is a 4-carbon acid which is subsequently decarboxylated. The CO2 thus released is refixed by the C3 cycle.
Both C4 and C3 plants exhibit a range of 13C/12C isotopic ratios, but typical values are ca. -10 to -14 per mil (C4) and -21 to -26 per mil (C3) [Weber et al., J. Agric. Food Chem., 45, 2942 (1997)]. Coal and petroleum fall generally in this latter range. The 13C measurement scale was originally defined by a zero set by pee dee belemnite (PDB) limestone, where values are given in parts per thousand deviations from this material. The "Δ13C", values are in parts per thousand (per mil), abbreviated %, and are calculated as follows:
δ 13 C ≡ ( 13 C / 12 C ) sample - ( 13 C / 12 C ) standard ( 13 C / 12 C ) standard × 100 % ( Equation 6 ) ##EQU00001##
Since the PDB reference material (RM) has been exhausted, a series of alternative RMs have been developed in cooperation with the IAEA, USGS, NIST, and other selected international isotope laboratories. Notations for the per mil deviations from PDB is Δ13C. Measurements are made on CO2 by high precision stable ratio mass spectrometry (IRMS) on molecular ions of masses 44, 45 and 46.
The fatty acid derivatives and the associated biofuels, chemicals, and mixtures may be completely distinguished from their petrochemical derived counterparts on the basis of 14C (fM) and dual carbon-isotopic fingerprinting, indicating new compositions of matter.
The fatty acid derivatives described herein have utility in the production of biofuels and chemicals. The new fatty acid derivative based product compositions provided by the instant invention additionally may be distinguished on the basis of dual carbon-isotopic fingerprinting from those materials derived solely from petrochemical sources. The ability to distinguish these products is beneficial in tracking these materials in commerce. For example, fuels or chemicals comprising both "new" and "old" carbon isotope profiles may be distinguished from fuels and chemicals made only of "old" materials. Hence, the instant materials may be followed in commerce on the basis of their unique profile and for the purposes of defining competition, and for determining shelf life.
In some examples a biofuel composition is made that includes a fatty acid derivative having δ13C of from about -10.9 to about -15.4, wherein the fatty acid derivative accounts for at least about 85% of biosourced material (derived from a renewable resource such as cellulosic materials and sugars) in the composition. In other examples, the biofuel composition includes a fatty acid derivative having the formula
X--(CH(R))nCH3 wherein X represents CH3, --CH2OR1; --C(O)OR2; or --C(O)NR3R4; R is, for each n, independently absent, H or lower aliphatic; n is an integer from 8 to 34, such as from 10 to 24; and R1, R2, R3 and R4 independently are selected from H and lower alkyl.Typically, when R is lower aliphatic, R represents a branched, unbranched or cyclic lower alkyl or lower alkenyl moiety. Exemplary R groups include, without limitation, methyl, isopropyl, isobutyl, sec-butyl, cyclopentenyl and the like. The fatty acid derivative is additionally characterized as having a δ13C of from about -10.9 to about -15.4; and the fatty acid derivative accounts for at least about 85% of biosourced material in the composition. In some examples the fatty acid derivative in the biofuel composition is characterized by having a fraction of modern carbon (fM14C) of at least about 1.003, 1.010, or 1.5.
B. Fatty Acid Derivatives
The centane number (CN), viscosity, melting point, and heat of combustion for various fatty acid esters have been characterized in for example, Knothe, Fuel Processing Technology 86:1059-1070, 2005, which is herein incorporated by reference. Using the teachings provided herein a production host can be engineered to produce anyone of the fatty acid esters described in the Knothe, Fuel Processing Technology 86:1059-1070, 2005.
Alcohols (short chain, long chain, branched or unsaturated) can be produced by the production hosts described herein. Such alcohols can be used as fuels directly or they can be used to create an ester, i.e. the A side of an ester as described above. Such ester alone or in combination with the other fatty acid derivatives described herein are useful a fuels.
Similarly, hydrocarbons produced from the microorganisms described herein can be used as biofuels. Such hydrocarbon based fuels can be designed to contain branch points, defined degrees of saturation, and specific carbon lengths. When used as biofuels alone or in combination with other fatty acid derivatives the hydrocarbons can be additionally combined with additives or other traditional fuels (alcohols, diesel derived from triglycerides, and petroleum based fuels).
The fatty acid derivatives described herein are useful for making bio-fuels. These fatty acid derivatives are made directly from fatty acids and not from the chemical processing of triglycerides. Accordingly, fuels comprising the disclosed fatty acid derivatives will contain less of the impurities than are normally associated with bio-fuels derived from triglycerides, such as fuels derived from vegetable oils and fats.
The crude fatty acid derivative bio-fuels described herein (prior to mixing the fatty acid derivative with other fuels such as traditional fuels) will contain less transesterification catalyst than petrochemical diesel or bio-diesel. For example, the fatty acid derivative can contain less than about 2%, 1.5%, 1.0%, 0.5%, 0.3%, 0.1%, 0.05%, or 0% of a transesterification catalyst or an impurity resulting from a transesterification catalyst. Transesterification catalysts include for example, hydroxide catalysts such as NaOH, KOH, LiOH, and acidic catalysts, such as mineral acid catalysts and Lewis acid catalysts. Catalysts and impurities resulting from transesterification catalysts include, without limitation, tin, lead, mercury, cadmium, zinc, titanium, zirconium, hafnium, boron, aluminum, phosphorus, arsenic, antimony, bismuth, calcium, magnesium, strontium, uranium, potassium, sodium, lithium, and combinations thereof.
Similarly, the crude fatty acid derivative bio-fuels described herein (prior to mixing the fatty acid derivative with other fuels such as petrochemical diesel or bio-diesel) will contain less glycerol (or glycerin) than bio-fuels made from triglycerides. For example, the fatty acid derivative can contain less than about 2%, 1.5%, 1.0%, .5%, .3%, .1%, .05%, or 0% glycerol.
The crude biofuel derived from fatty acid derivatives will also contain less free alcohol (i.e. alcohol that is used to create the ester) than bio-diesel made from triglycerides. This is in-part due to the efficiency of utilization of the alcohol by the production host. For example, the fatty acid derivative will contain less than about 2%, 1.5%, 1.0%, 0.5%, 0.3%, 0.1%, 0.05%, or 0% free alcohol.
Biofuel derived from the disclosed fatty acid derivatives can be additionally characterized by its low concentration of sulfur compared to petroleum derived diesel. For example, biofuel derived from fatty acid derivatives can have less than about 2%, 1.5%, 1.0%, 0.5%, 0.3%, 0.1%, 0.05%, or 0% sulfur.
Fuel additives are used to enhance the performance of a fuel or engine. For example, fuel additives can be used to alter the freezing/gelling point, cloud point, lubricity, viscosity, oxidative stability, ignition quality, octane level, and flash point. In the United States, all fuel additives must be registered with Environmental Protection Agency and companies that sell the fuel additive and the name of the fuel additive are publicly available on the agency website and also by contacting the agency. One of ordinary skill in the art will appreciate that the fatty acid derivatives described herein can be mixed with one or more such additives to impart a desired quality.
One of ordinary skill in the art will also appreciate that the fatty acid derivatives described herein are can be mixed with other fuels such as bio-diesel derived from triglycerides, various alcohols such as ethanol and butanol, and petroleum derived products such as gasoline. In some examples, a fatty acid derivative, such as C16:1 ethyl ester or C18:1 ethyl ester, is produced which has a low gel point. This low gel point fatty acid derivative is mixed with bio-diesel made from triglycerides to lessen the overall gelling point of the fuel. Similarly, a fatty acid derivative such as C16:1 ethyl ester or C18:1 ethyl ester can be mixed with petroleum derived diesel to provide a mixture that is at least and often greater than 5% biodiesel. In some examples, the mixture includes at least 20% or greater of the fatty acid derivative.
For example, a biofuel composition can be made that includes at least about 20%, 30%, 40%, 50%, 60%, 70%, 80%, 85%, 90% or 95% of a fatty acid derivative that includes a carbon chain that is 8:0, 10:0, 12:0, 14:0, 14:1, 16:0, 16:1, 18:0, 18:1, 18:2, 18:3, 20:0, 20:1, 20:2, 20:3, 22:0, 22:1 or 22:3. Such biofuel compositions can additionally include at least one additive selected from a cloud point lowering additive that can lower the cloud point to less than about 5° C., or 0° C., a surfactant, or a microemulsion, at least about 5%, 10%, 15%, 20%, 30%, 40%, 50%, 60%, 70% or 80%, 85%, 90%, or 95% diesel fuel from triglycerides, petroleum derived gasoline or diesel fuel from petroleum.
FIG. 1 is a diagram of the FAS pathway showing the enzymes directly involved in the synthesis of acyl-ACP. To increase the production of waxes/fatty acid esters, and fatty alcohols one or more of the enzymes can be over expressed or mutated to reduce feedback inhibition. Additionally, enzymes that metabolize the intermediates to make non-fatty acid based products (side reactions) can be functionally deleted or attenuated to increase the flux of carbon through the fatty acid biosynthetic pathway. Examples 1, 2, and 8 below provide exemplary production hosts that have been modified to increase fatty acid production.
FIGS. 2, 3 and 4 show biosynthetic pathways that can be engineered to make fatty alcohols and wax/fatty acid esters, respectively. As illustrated in FIG. 2 the conversion of each substrate (acetyl-CoA, malonyl-CoA, acyl-ACP, fatty acid, and acyl-CoA) to each product (acetyl-CoA, malonyl-CoA, acyl-ACP, fatty acid, and acyl-CoA) can be accomplished using several different polypeptides that are members of the enzyme classes indicated. The Examples below describe microorganisms that have been engineered or can be engineered to produce specific fatty alcohols and waxes/fatty acid esters and hydrocarbons.
Production Host Construction
An exemplary production host is LS9001. LS9001 was produced by modifying C41(DE3) from Overexpress.com (Saint Beausine, France) to functionally deleting the fadE gene (acyl-CoA dehydrogenase).
Briefly, the fadE knock-out strain of E. coli was made using primers YafV_NotI and Ivry_Ol to amplify about 830 by upstream of fadE and primers Lpcaf_ol and LpcaR_Bam to amplify about 960 by downstream of fadE. Overlap PCR was used to create a construct for in frame deletion of the complete fadE gene. The fadE deletion construct was cloned into the temperature sensitive plasmid pKOV3, which contained a SacB gene for counterselection, and a chromosomal deletion of fadE was made according to the method of Link et al., J. Bact. 179:6228-6237, 1997. The resulting strain was not capable of degrading fatty acids and fatty acyl-CoAs (this functional deletion is herein designated as ΔfadE)
Additional modifications that can be included in a production host include introducing a plasmid carrying the four genes which are responsible for acetyl-CoA carboxylase activity in E. coli (accA, B, C, and D, Accessions: NP--414727, NP--417721, NP--417722, NP--416819, EC 126.96.36.199). The accABCD genes were cloned in two steps as bicistronic operons into the NcoI/HindIII and NdeI/AvrII sites of pACYCDuet-1 (Novagen, Madison, Wis.) the resulting plasmid was termed pAS004.126.
Additional modifications that can be included in a production host include the following: over-expression of aceEF (encoding the E1p dehydrogase component and the E2p dihydrolipoamide acyltransferase component of the pyruvate and 2-oxoglutarate dehydrogenase complexes); and fabH/fabD/fabG/acpP/fabF (encoding FAS) from any organism known in the art to encode such proteins, including for example E. coli, Nitrosomonas europaea (ATCC 19718), Bacillus subtilis, Saccharomyces cerevisiae, Streptomyces spp, Ralstonia, Rhodococcus, Corynebacteria, Brevibacteria, Mycobacteria, oleaginous yeast, and the like can be expressed in the production host. Similarly, production hosts can be engineered to express accABCD (encoding acetyl co-A carboxylase) from Pisum savitum instead of, or in addition to, the E. coli homologues. However, when the production host is also producing butanol it is less desirable to express the Pisum savitum homologue.
In some exemplary production hosts, genes can be knocked out or attenuated using the method of Link, et al., J. Bacteriol. 179:6228-6237, 1997. For example, genes that can be knocked out or attenuated include gpsA (encoding biosynthetic sn-glycerol 3-phosphate dehydrogenase, accession NP--418065, EC: 188.8.131.52); ldhA (encoding lactate dehydrogenase, accession NP--415898, EC: 184.108.40.206); pflb (encoding formate acetyltransferase 1, accessions: P09373, EC: 220.127.116.11); adhE (encoding alcohol dehydrogenase, accessions: CAA47743, EC: 18.104.22.168, 22.214.171.124); pta (encoding phosphotransacetylase, accessions: NP--416800, EC: 126.96.36.199); poxB (encoding pyruvate oxidase, accessions: NP--415392, EC: 188.8.131.52); ackA (encoding acetate kinase, accessions: NP--416799, EC: 184.108.40.206) and combinations thereof.
Similarly, the PlsB[D311E] mutation can be introduced into LS9001 to attenuate PlsB using the method described above for the fadE deletion. Once introduced, this mutation will decrease the amount of carbon being diverted to phospholipid production (see, FIG. 1). Briefly, an allele encoding PlsB[D311E] is made by replacing the GAC codon for aspartate 311 with a GAA codon for glutamate. The altered allele is made by gene synthesis and the chromosomal plsB wildtype allele is exchanged for the mutant plsB[D311E] allele using the method of Link et al. (see above).
Production Host Modifications
The following plasmids were constructed for the expression of various proteins that are used in the synthesis of fatty acid derivatives. The constructs were made using standard molecular biology methods and all the cloned genes were put under the control of IPTG-inducible promoters (T7, tac or lac promoters).
The 'tesA gene (thioesterase A gene accession NP--415027 without leader sequence (Cho and Cronan, The J. of Biol. Chem., 270:4216-9, 1995, EC: 220.127.116.11, 3.1.2.-) of E. coli was cloned into NdeI/AvrII digested pETDuet-1 (pETDuet-1 described herein is available from Novagen, Madison, Wis.). Genes encoding for FatB-type plant thioesterases (TEs) from Umbellularia California, Cuphea hookeriana and Cinnamonum camphorum (accessions: UcFatB1=AAA34215, ChFatB2=AAC49269, ChFatB3=AAC72881, CcFatB=AAC49151 were individually cloned into three different vectors: (i) NdeI/AvrII digested pETDuet-1, (ii)XhoI/HindIII digested pBluescript KS+ (Stratagene, La Jolla, Calif.)(used to create N-terminal lacZ::TE fusion proteins) and (iii)XbaI/HindIII digested pMAL-c2X (New England Lab, Ipswich, Mass.) (used to create n-terminal MalE::TE fusions). The fadD gene (encoding acyl-CoA synthetase) from E. coli was cloned into a NcoI/HindIII digested pCDFDuet-1 derivative, which contained the acr1 gene (acyl-CoA reductase) from Acinetobacter baylyi ADP1 within its NdeI/AvrII sites. Table 7 provides a summary of the plasmids generated to make several exemplary production strains, one of ordinary skill in the art will appreciate that different plasmids and genomic modifications can be used to achieve similar strains.
TABLE-US-00007 TABLE 7 Summary of Plasmids used in Production hosts Source Organism Plasmid Gene Product Accession No., EC number pETDuet-1-tesA E. coli Accessions: NP_415027, TesA EC: 18.104.22.168, 3.1.2.- pETDuet-1-TEuc Umbellularia Q41635 pBluescript-TEuc California pMAL-c2X-TEuc UcFatB1 AAA34215 pETDuet-1-TEch Cuphea hookeriana ABB71581 pBluescript-TEch ChFatB2 AAC49269 pMAL-c2X-TEch ChFatB3 AAC72881 pETDuet-1-TEcc Cinnamonun pBluescript-TEcc camphorum AAC49151 TEci CcFatB pCDFDuet-1- E. coli fadD: Accessions NP_416319, fadD-acr1 EC 22.214.171.124 acr1: Accessions YP_047869
The chosen expression plasmids contain compatible replicons and antibiotic resistance markers, so that a four-plasmid expression system can be established. Therefore, LS9001 can be co-transformed with (i) any of the TE-expressing plasmids, (ii) the FadD-expressing plasmid, which also expresses acr1 and (iii) wax synthase expression plasmid. When induced with IPTG, the resulting strain will produce increased concentrations of fatty-alcohols from carbon sources such as glucose. The carbon chain length and degree of saturation of the fatty alcohol produced is dependent on the thioesterase gene that is expressed.
Production of Fatty Alcohol in the Recombinant E. coli Strain
Fatty alcohols were produced by expressing a thioesterase gene and an acyl-CoA reductase gene (FAR) exogenously in a production host. More specifically, plasmids pCDFDuet-1-fadD-acr1 (acyl-CoA reductase) and pETDuet-1-'tesA (thioesterase) were transformed into E. coli strain LS9001 (described in Example 1) and corresponding transformants were selected in LB plate supplemented with 100 mg/L of spectinomycin and 50 mg/L of carbenicillin. Four transformants of LS9001/pCDFDuet-1-fadD-acr1 were independently inoculated into 3 mL of M9 medium supplemented with 50 mg/L of carbenicillin and 100 mg/L of spectinomycin). The samples containing the transformants were grown in at 25° C. in a shaker (250 rpm) until they reached 0.5 OD600. 1.5 mL of each sample was transferred into a 250 mL flask containing 30 mL of the medium described above. The resulting culture was grown at 25° C. in a shaker until the culture reached between 0.5-1.0 OD600. IPTG was then added to a final concentration of 1 mM. and growth continued for 40 hours.
The cells were then spun down at 4000 rpm and the cell pellets were suspended in 1.0 mL of methanol. 3 mL of ethyl acetate was then mixed with the suspended cells. 3 mL of H2O were then added to the mixture and the mixture was sonicated for 20 minutes. The resulting sample was centrifuged at 4000 rpm for 5 minutes and the organic phase (the upper phase) which contained fatty alcohol and was subjected to GC/MS analysis. Total alcohol (including tetradecanol, hexadecanol, hexadecenol and octadecenol) yield was about 1-10 mg/L. When an E. coli strain carrying only empty vectors was cultured in the same way, only 0.2-0.5 mg/L of fatty alcohols were found in the ethyl acetate extract.
Production and Release of Fatty Alcohol from Production Host
Acr1 (acyl-CoA reductase) was expressed in E. coli grown on glucose as the sole carbon and energy source. The E. coli produced small amounts of fatty alcohols such as dodecanol (C12:0-OH), tetradecanol (C14:0-OH) and hexadecanol (C16:0-OH). In other samples, FadD (acyl-CoA synthetase) was expressed together with acr1 in E. coli and a five-fold increase in fatty alcohol production was observed.
In other samples, acr1, fadD, accABCD (acetyl-CoA Carboxylase) (plasmid carrying accABCD constructed as described in Example 1) were expressed along with various individual thioesterases (TEs) in wildtype E. coliC41(DE3) and an E. coli C41(DE3 ΔfadE, a strain lacking acyl-CoA dehydrogenase. This resulted in additional increases in fatty alcohol production and modulating the profiles of fatty alcohols (see FIG. 5). For example, over-expression of E. coli 'tesA (pETDuet-1-'tesA) in this system achieved approximately a 60-fold increase in C12:0-OH, C14:0-OH and C16:0-OH with C14:0-OH being the major fatty alcohol. A very similar result was obtained when the ChFatB3 enzyme (FatB3 from Cuphea hookeriana in pMAL-c2X-TEcu) was expressed. When the UcFatB1 enzyme (FatB1 from Umbellularia californicain in pMAL-c2X-TEuc) was expressed, fatty alcohol production increased approximately 20-fold and C12:0-OH was the predominant fatty alcohol.
Expression of ChFatB3 and UcFatB1 also led to the production of significant amounts of the unsaturated fatty alcohols C16:1-OH and C14:1-OH, respectively. The presence of fatty alcohols was also found in the supernatant of samples generated from the expression of tesA (FIG. 6). At 37° C. approximately equal amounts of fatty alcohols were found in the supernatant and in the cell pellet, whereas at 25° C. approximately 25% of the fatty alcohols were found in the supernatant.
Medium Chain Fatty Acid Esters
Alcohol acetyl transferases (AATs, EC 126.96.36.199), which is responsible for acyl acetate production in various plants, can be used to produce medium chain length waxes, such as octyl octanoate, decyl octanoate, decyl decanoate, and the like. Fatty esters, synthesized from medium chain alcohol (such as C6, C8) and medium chain acyl-CoA (or fatty acids, such as C6 or C8) have a relative low melting point. For example, hexyl hexanoate has a melting point of -55° C. and octyl octanoate has a melting point of -18 to -17° C. The low melting points of these compounds makes them good candidates for use as biofuels.
In this example, a SAAT gene was co-expressed in a production host C41(DE3, ΔfadE) with fadD from E. coli and acr1 (alcohol reductase from A. baylyi ADP1) and octanoic acid was provided in the fermentation broth. This resulted in the production of octyl octanoate. Similarly, when the wax synthase gene from A. baylyi ADP1was expressed in the production host instead of the SAAT gene octyl octanoate was produced.
A recombinant SAAT gene was synthesized using DNA 2.0 (Menlo Park, Calif. 94025). The synthesized DNA was based on the published gene sequence (accession number AF193789) and modified to eliminate the NcoI site. The synthesized SAAT gene (as a BamHI-HindIII fragment) was cloned in pRSET B (Invitrogen, Calsbad, Calif.), linearized with BamHI and HindIII. The resulted plasmid, pHZ1.63A was cotransformed into an E. coli production host with pAS004.114B, which carries a fadD gene from E. coli and acr1 gene from A. baylyi ADP1. The transformants were grown in 3 mL of M9 medium with 2% of glucose. After IPTG induction and the addition of 0.02% of octanoic acid, the culture was continued at 25° C. from 40 hours. After that, 3 mL of acetyl acetate was added to the whole culture and mixed several times with mixer. The acetyl acetate phase was analyzed by GC/MS.
Surprising, in the acetyl acetate extract, there is no acyl acetate found. However, a new compound was found and the compound was octyl octanoate. Whereas the control strain without the SAAT gene [C41(DE3, ΔfadE)/pRSET B+pAS004.114B] did not produce octyl octanoate. Also the strain [C41(DE3, ΔfadE)/pHZ1.43 B+pAS004.114B], in which the wax synthase gene from A. baylyi ADP1 was carried by pHZ1.43 produced octyl octanoate (see FIG. 7B).
The finding that SAAT activity produces octyl octanoate has not reported before and makes it possible to produce medium chain waxes such as octyl octanoate, octyl decanoate, which have low melting point and are good candidates to be use for biofuel to replace triglyceride based biodiesel.
Production of Wax Ester in E. coli Strain LS9001
Wax esters were produced by engineering an E. coli production host to express a fatty alcohol forming acyl-CoA reductase, thioesterase, and a wax synthase. Thus, the production host produced both the A and the B side of the ester and the structure of both sides was influenced by the expression of the thioesterase gene.
More specifically, wax synthase from A. baylyi ADP1 (termed WSadp1, accessions AA017391, EC: 2.3.175) was amplified with the following primers using genomic DNA from A. baylyi ADP1 as the template. The primers were (1) WSadp1_NdeI, 5'-TCATATGCGCCCATTACATCCG-3' and (2) WSadp1_Avr, 5'-TCCTAGGAGGGCTAATTTAGCCCTTTAGTT-3'. The PCR product was digested with NdeI and AvrII and cloned into pCOALDeut-1 to give pHZ 1.43. The plasmid carrying WSadp1 was then co-transformed into E. coli strain LS9001 with both pETDuet-1'tesA and pCDFDuet-1-fadD-acr1 and transformants were selected in LB plates supplemented with 50 mg/L of kanamycin, 50 mg/L of carbenicillin and 100 mg/L of spectinomycin. Three transformants were inoculated in 3 mL of LBKCS (LB broth supplement with 50 mg/L of kanamycin, 50 mg/L of carbenicillin, 100 mg/L of spectinomycin and 10 g/L of glucose) and cultured at 37° C. shaker (250 rpm). When the cultures reached 0.5 OD600, 1.5 mL of each culture was transferred into 250 mL flasks containing 50 mL of LBKCS and the flasks were grown in a shaker (250 rpm) at 37° C. until the culture reached 0.5-1.0 OD600. IPTG was then added to a final concentration of 1 mM. The induced cultures were grown at 37° C. shaker for another 40-48 hours.
The culture was then placed into 50 mL conical tubes and the cells were spun down at 3500×g for 10 minutes. The cell pellet was then mixed with 5 mL of ethyl acetate. The ethyl acetate extract was analyzed with GC/MS. The intracellular yield of waxes (including C16C16, C14:1C16, C18:1C18:1,C2C14, C2C16, C2C16:1, C16C16:1 and C2C18:1) was about 10 mg/L. When an E. coli strain only carrying empty vectors was cultured in the same way, only 0.2 mg/L of wax was found in the ethyl acetate extract.
Production and Release of Fatty-Ethyl Ester from Production Host
The LS9001 strain was modified by transforming it with the plasmids carrying a wax synthase gene from A. baylyi (plasmid pHZ1.43), a thioesterase gene from Cuphea hookeriana (plasmid pMAL-c2X-TEcu) and a fadD gene from E. coli (plasmid pCDFDuet-1-fadD). This recombinant strain was grown at 25° C. in 3 mL of M9 medium with 50 mg/L of kanamycin, 100 mg/L of carbenicillin and 100 mg/L of spectinomycin. After IPTG induction, the media was adjusted to a final concentration of 1% ethanol and 2% glucose. The culture was allowed to grow for 40 hours after IPTG induction. The cells were separated from the spent medium by centrifugation at 3500×g for 10 minutes). The cell pellet was re-suspended with 3 mL of M9 medium. The cell suspension and the spent medium were then extracted with 1 volume of ethyl acetate. The resulting ethyl acetate phases from the cells suspension and the supernatant were subjected to GC-MS analysis. The results showed that the C16 ethyl ester was the most prominent ester species (as expected for this thioesterase, see Table 1), and that 20% of the fatty acid ester produced was released from the cell (see FIG. 8). A control E. coli strain C41(DE3, ΔfadE) containing pCOLADuet-1 (empty vector for the wax synthase gene), pMAL-c2X-TEuc (containing fatB from U. california) and pCDFDuet-1-fadD (fadD gene from E. coli) failed to produce detectable amounts of fatty ethyl esters. The fatty acid esters were quantified using commercial palmitic acid ethyl ester as the reference. Fatty acid esters were also made using the methods described herein except that methanol, or isopropanol was added to the fermentation broth and the expected fatty acid esters were produced.
The Influence of Various Thioesterases on the Composition of Fatty-Ethyl Esters Produced in Recombinant E. coli Strains
The thioesterases FatB3 (C. hookeriana), TesA (E. coli), and FatB (U. california) were expressed simultaneously with wax synthase (A. baylyi). A plasmid termed pHZ1.61 was constructed by replacing the NotI-AvrII fragment (carrying the acr1 gene) with the NotI-AvrII fragment from pHZ1.43 so that fadD and the ADP1 wax synthase were in one plasmid and both coding sequences were under the control of separate T7 promoter. The construction of pHZ1.61 made it possible to use a two plasmid system instead of the three plasmid system as described in Example 6. pHZ1.61 was then co-transformed into E. coli C41(DE3, ΔfadE) with one of the various plasmids carrying the different thioesterase genes stated above.
The total fatty acid ethyl esters (supernatant and intracellular fatty acid ethyl esters) produced by these transformants were evaluated using the technique described herein. The yields and the composition of fatty acid ethyl esters are summarized in Table 8.
TABLE-US-00008 TABLE 8 The yields (mg/L) and the composition of fatty acid ethyl esters by recombinant E. coli C41(DE3, ΔfadE)/pHZ1.61 and plasmids carrying various thioesterase genes. Thioesterases C2C10 C2C12:1 C2C12 C2C14:1 C2C14 C2C16:1 C2C16 C2C18:1 Total `TesA 0.0 0.0 6.5 0.0 17.5 6.9 21.6 18.1 70.5 ChFatB3 0.0 0.0 0.0 0.0 10.8 12.5 11.7 13.8 48.8 ucFatB 6.4 8.5 25.3 14.7 0.0 4.5 3.7 6.7 69.8 pMAL 0.0 0.0 0.0 0.0 5.6 0.0 12.8 7.6 26.0 Note: `TesA, pETDuet-1-`tesA; ChFatB3, pMAL-c2X-TEcu; ucFatB, pMAL-c2X-TEuc; pMAL, pMAL-c2X, the empty vector for thioesterase genes used in the study.
Production Host Construction
The genes that control fatty acid production are conserved between microorganisms. For example, Table 9 identifies the homologues of many of the genes described herein which are known to be expressed in microorganisms that produce hydrocarbons. To increase fatty acid production and, therefore, hydrocarbon production in microorganisms such as those identified in Table 9, heterologous genes, such as those from E. coil can be expressed. One of ordinary skill in the art will also appreciate that genes that are endogenous to the micoorganisms provided in Table 9 can also be over-expressed, or attenuated using the methods described herein. Moreover, genes that are described in FIG. 10 can be expressed or attenuated in microorganisms that endogenously produce hydrocarbons to allow for the production of specific hydrocarbons with defined carbon chain length, saturation points, and branch points.
For example, exogenous nucleic acid sequences encoding acetyl-CoA carboxylase are introduced into K. radiotolerans. The following genes comprise the acetyl-CoA carboxylase protein product in K. radiotolerans; acetyl CoA carboxylase, alpha subunit (accA/ZP--00618306), acetyl-CoA carboxylase, biotin carboxyl carrier protein (accB/ZP--00618387), acetyl-CoA carboxylase, biotin carboxylase subunit (accC/ZP--00618040), and acetyl-CoA carboxylase, beta (carboxyltranferase) subunit (accD/ZP--00618306). These genes are cloned into a plasmid such that they make a synthetic acetyl-CoA carboxylase operon (accABCD) under the control of a K. radiotolerans expression system such as the expression system disclosed in Ruyter et al., Appl Environ Microbiol. 62:3662-3667, 1996. Transformation of the plasmid into K. radiotolerans will enhance fatty acid production. The hydrocarbon producing strain of K. radiotolerans can also be engineered to make branched, unsaturated hydrocarbons having specific carbon chain lengths using the methods disclosed herein.
TABLE-US-00009 TABLE 9 Hydrocarbon production hosts Organism Gene Name Accession No./Seq ID/Loci EC No. Desulfovibrio desulfuricans G20 accA YP_388034 188.8.131.52 Desulfovibrio desulfuricans G22 accC YP_388573/YP_388033 184.108.40.206, 220.127.116.11 Desulfovibrio desulfuricans G23 accD YP_388034 18.104.22.168 Desulfovibrio desulfuricans G28 fabH YP_388920 22.214.171.124 Desulfovibrio desulfuricans G29 fabD YP_388786 126.96.36.199 Desulfovibrio desulfuricans G30 fabG YP_388921 188.8.131.52 Desulfovibrio desulfuricans G31 acpP YP_388922/YP_389150 184.108.40.206, 220.127.116.11, 18.104.22.168 Desulfovibrio desulfuricans G32 fabF YP_388923 22.214.171.124 Desulfovibrio desulfuricans G33 gpsA YP_389667 126.96.36.199 Desulfovibrio desulfuricans G34 ldhA YP_388173/YP_390177 188.8.131.52, 184.108.40.206 Erwinia (micrococcus) amylovora accA 942060-943016 220.127.116.11 Erwinia (micrococcus) amylovora accB 3440869-3441336 18.104.22.168 Erwinia (micrococcus) amylovora accC 3441351-3442697 22.214.171.124, 126.96.36.199 Erwinia (micrococcus) amylovora accD 2517571-2516696 188.8.131.52 Erwinia (micrococcus) amylovora fadE 1003232-1000791 1.3.99.- Erwinia (micrococcus) amylovora plsB(D311E) 333843-331423 184.108.40.206 Erwinia (micrococcus) amylovora aceE 840558-843218 220.127.116.11 Erwinia (micrococcus) amylovora aceF 843248-844828 18.104.22.168 Erwinia (micrococcus) amylovora fabH 1579839-1580789 22.214.171.124 Erwinia (micrococcus) amylovora fabD 1580826-1581749 126.96.36.199 Erwinia (micrococcus) amylovora fabG CAA74944 188.8.131.52 Erwinia (micrococcus) amylovora acpP 1582658-1582891 184.108.40.206, 220.127.116.11, 18.104.22.168 Erwinia (micrococcus) amylovora fabF 1582983-1584221 22.214.171.124 Erwinia (micrococcus) amylovora gpsA 124800-125810 126.96.36.199 Erwinia (micrococcus) amylovora ldhA 1956806-1957789 188.8.131.52, 184.108.40.206 Kineococcus radiotolerans accA ZP_00618306 220.127.116.11 SRS30216 Kineococcus radiotolerans accB ZP_00618387 18.104.22.168 SRS30216 Kineococcus radiotolerans accC ZP_00618040/ 22.214.171.124, 126.96.36.199 SRS30216 ZP_00618387 Kineococcus radiotolerans accD ZP_00618306 188.8.131.52 SRS30216 Kineococcus radiotolerans fadE ZP_00617773 1.3.99.- SRS30216 Kineococcus radiotolerans plsB(D311E) ZP_00617279 184.108.40.206 SRS30216 Kineococcus radiotolerans aceE ZP_00617600 220.127.116.11 SRS30216 Kineococcus radiotolerans aceF ZP_00619307 18.104.22.168 SRS30216 Kineococcus radiotolerans fabH ZP_00618003 22.214.171.124 SRS30216 Kineococcus radiotolerans fabD ZP_00617602 126.96.36.199 SRS30216 Kineococcus radiotolerans fabG ZP_00615651 188.8.131.52 SRS30216 Kineococcus radiotolerans acpP ZP_00617604 184.108.40.206, SRS30216 220.127.116.11, 18.104.22.168 Kineococcus radiotolerans fabF ZP_00617605 22.214.171.124 SRS30216 Kineococcus radiotolerans gpsA ZP_00618825 126.96.36.199 SRS30216 Kineococcus radiotolerans ldhA ZP_00618879 188.8.131.52, SRS30216 184.108.40.206 Rhodospirillum rubrum accA YP_425310 220.127.116.11 Rhodospirillum rubrum accB YP_427521 18.104.22.168 Rhodospirillum rubrum accC YP_427522/YP_425144/YP_427028/ 22.214.171.124, 126.96.36.199 YP_426209/ YP_427404 Rhodospirillum rubrum accD YP_428511 188.8.131.52 Rhodospirillum rubrum fadE YP_427035 1.3.99.- Rhodospirillum rubrum aceE YP_427492 184.108.40.206 Rhodospirillum rubrum aceF YP_426966 220.127.116.11 Rhodospirillum rubrum fabH YP_426754 18.104.22.168 Rhodospirillum rubrum fabD YP_425507 22.214.171.124 Rhodospirillum rubrum fabG YP_425508/YP_425365 126.96.36.199 Rhodospirillum rubrum acpP YP_425509 188.8.131.52, 184.108.40.206, 220.127.116.11 Rhodospirillum rubrum fabF YP_425510/YP_425510/ 18.104.22.168 YP_425285 Rhodospirillum rubrum gpsA YP_428652 22.214.171.124 Rhodospirillum rubrum ldhA YP_426902/YP_428871 126.96.36.199, 188.8.131.52 Vibrio furnissii accA 1, 16 184.108.40.206 Vibrio furnissii accB 2, 17 220.127.116.11 Vibrio furnissii accC 3, 18 18.104.22.168, 22.214.171.124 Vibrio furnissii accD 4, 19 126.96.36.199 Vibrio furnissii fadE 5, 20 1.3.99.- Vibrio furnissii plsB(D311E) 6, 21 188.8.131.52 Vibrio furnissii aceE 7, 22 184.108.40.206 Vibrio furnissii aceF 8, 23 220.127.116.11 Vibrio furnissii fabH 9, 24 18.104.22.168 Vibrio furnissii fabD 10, 25 22.214.171.124 Vibrio furnissii fabG 11, 26 126.96.36.199 Vibrio furnissii acpP 12, 27 188.8.131.52, 184.108.40.206, 220.127.116.11 Vibrio furnissii fabF 13, 28 18.104.22.168 Vibrio furnissii gpsA 14, 29 22.214.171.124 Vibrio furnissii ldhA 15, 30 126.96.36.199, 188.8.131.52 Stenotrophomonas maltophilia accA ZP_01643799 184.108.40.206 R551-3 Stenotrophomonas maltophilia accB ZP_01644036 220.127.116.11 R551-3 Stenotrophomonas maltophilia accC ZP_01644037 18.104.22.168, 22.214.171.124 R551-3 Stenotrophomonas maltophilia accD ZP_01644801 126.96.36.199 R551-3 Stenotrophomonas maltophilia fadE ZP_01645823 1.3.99.- R551-3 Stenotrophomonas maltophilia plsB(D311E) ZP_01644152 188.8.131.52 R551-3 Stenotrophomonas maltophilia aceE ZP_01644724 184.108.40.206 R551-3 Stenotrophomonas maltophilia aceF ZP_01645795 220.127.116.11 R551-3 Stenotrophomonas maltophilia fabH ZP_01643247 18.104.22.168 R551-3 Stenotrophomonas maltophilia fabD ZP_01643535 22.214.171.124 R551-3 Stenotrophomonas maltophilia fabG ZP_01643062 126.96.36.199 R551-3 Stenotrophomonas maltophilia acpP ZP_01643063 188.8.131.52, R551-3 184.108.40.206, 220.127.116.11 Stenotrophomonas maltophilia fabF ZP_01643064 18.104.22.168 R551-3 Stenotrophomonas maltophilia gpsA ZP_01643216 22.214.171.124 R551-3 Stenotrophomonas maltophilia ldhA ZP_01645395 126.96.36.199, R551-3 188.8.131.52 For Table 9, Accession Numbers are from GenBank, Release 159.0 as of Apr. 15, 2007, EC Numbers are from KEGG, Release 42.0 as of April 2007 (plus daily updates up to and including May 09, 2007), results for Erwinia amylovora strain Ea273 are taken from the Sanger sequencing center, completed shotgun sequence as of May 09, 2007, positions for Erwinia represent locations on the Sanger psuedo-chromosome, sequences from Vibrio furnisii M1 are from the LS9 VFM1 pseudochromosome, v2 build, as of Sep. 28, 2006, and include the entire gene, and may also include flanking sequence
Additional Exemplary Production Strains
Table 10, below provides additional exemplary production strains. Two example biosynthetic pathways are described for producing fatty acids, fatty alcohols, and wax esters. A genetically engineered host can be produced by cloning the expression of the accABCD genes from E. coli, the 'tesA gene from E. coli, and fadD gene from E. coli into a host cell. Host cells can be selected from E. coli, yeast, add to the list. These genes can also be transformed into a host cell that is modified to contain one or more of the genetic manipulations described in Examples 1 and 2, above. As provided in Table 10, additional production hosts can be created using the indicated exogenous genes.
TABLE-US-00010 TABLE 10 Combination of genes useful for making genetically engineered production strains Sources of Fatty acids Fatty alcohols wax/fatty esters Peptide genes Genes example 1 example 2 example 1 example 2 example 1 example 2 acetyl-CoA E. coli accABCD X X X X X X carboxylase thio- E. coli tesA X X X X esterase Cinnamomum ccFatB camphora Umbellularia umFatB X X californica Cuphea chFatB2 hookeriana Cuphea chFatB3 hookeriana Cuphea chFatA hookerian Arabidopsis AtFatA1 thaliana Arabidopsis AtFatB1[M141T] thalian acyl-CoA E. coli fadD X X X X X X synthase acyl-CoA Bombyx mori bFAR reductase Acinetobacter acr 1 X X baylyi L ADP1 Simmondsia jjFAR X X chinensis Triticum aestivum Mus mFAR1 musculus Mus mFAR2 musculus Acinetpbacter acr M1 sp M1 Homo hFAR sapiens wax Fundibacter WST9 synthase/ jadensis DSM alcohol 12178 acyltransferase Acinetobacter WSHN X sp. HO1-N Acinetobacter WSadp1 X baylyi ADP1 Mus mWS musculus Homo hWS sapiens Fragaria x SAAT ananassa Malus x MpAAT domestica Simmondsia JjWS chinensis (AAD38041) Decarbonylase Arabidopsis cer1 thaliana Oryza sativa cer1 Transporter Acinetobacter X X sp. HO1-N Arabidopsis Cer5 thaliana
Host microorganisms can be also engineered to express umuC and umuD from E. coli in pBAD24 under the prpBCDE promoter system through de novo synthesis of this gene with the appropriate end-product production genes. For small scale hydrocarbon product production, E. coli BL21(DE3) cells harbouring pBAD24 (with ampicillin resistance and the end-product synthesis pathway) as well as pUMVC1 (with kanamycin resistance and the acetyl CoA/malonyl CoA over-expression system) are incubated overnight at at 37° C. shaken at >200 rpm 2L flasks in 500 ml LB medium supplemented with 75 μg/mL ampicillin and 50 μg/ml kanamycin until cultures reached an OD600 of >0.8. Upon achieving an OD600 of >0.8, cells are supplemented with 25 mM sodium proprionate (pH 8.0) to activate the engineered gene systems for production as well as to stop cellular proliferation (through activation of umuC and umuD proteins). Induction is performed for 6 hours at 30° C. After incubation, media is examined for product using GC-MS (as described below).
For large scale product production, the engineered microorganisms are grown in 10 L, 100 L or larger batches, fermented and induced to express desired products based on the specific genes encoded in plasmids as appropriate. E. coli BL21(DE3) cells harbouring pBAD24 (with ampicillin resistance and the end-product synthesis pathway) as well as pUMVC1 (with kanamycin resistance and the acetyl-CoA/malonyl-CoA over-expression system) are incubated from a 500 mL seed culture for 10 L fermentations (5 L for 100 L fermentations) in LB media (glycerol free) at 37° C. shaken at >200 rpm until cultures reached an OD600 of >0.8 (typically 16 hours) incubated with 50 μg/mL kanamycin and 75 μg/mL ampicillin. Media is treated with continuously supplemented to maintain a 25 mM sodium proprionate (pH 8.0) to activate the engineered in gene systems for production as well as to stop cellular proliferation (through activation of umuC and umuD proteins). Media is continuously supplemented with glucose to maintain a concentration 90 g/100 mL. After the first hour of induction, aliquots of no more than 10% of the total cell volume are removed each hour and allowed to sit unaggitated so as to allow the hydrocarbon product to rise to the surface and undergo a spontaneous phase separation. The hydrocarbon component is then collected and the aqueous phase returned to the reaction chamber. The reaction chamber is operated continuously. When the OD600 drops below 0.6, the cells are replaced with a new batch grown from a seed culture.
For wax ester production, subsequent to isolation, the wax esters are washed briefly in 1 M HCl to split the ester bond, and returned to pH 7 with extensive washing with distilled water.
To characterize and quantify the fatty alcohols and fatty acid esters, gas chromatography (GC) coupled with electron impact mass spectra (MS) detection was used. Fatty alcohol samples were first derivatized with an excess of N-trimethylsilyl (TMS) imidazole to increase detection sensitivity. Fatty acid esters did not required derivatization. Both fatty alcohol-TMS derivatives and fatty acid esters were dissolved in an appropriate volatile solvent, like ethyl acetate. The samples were analyzed on a 30 m DP-5 capillary column using the following method. After a 1 μL splitless injection onto the GC/MS column, the oven is held at 100° C. for 3 minutes. The temperature was ramped up to 320° C. at a rate of 20° C./minute. The oven was held at 320° C. for an additional 5 minutes. The flow rate of the carrier gas helium was 1.3 mL/minute. The MS quadrapole scans from 50 to 550 m/z. Retention times and fragmentation patterns of product peaks were compared with authentic references to confirm peak identity.
For example, hexadeconic acid ethyl ester eluted at 10.18 minutes (FIGS. 9A and 9B). The parent ion of 284 mass units was readily observed. More abundent were the daughter ions produced during mass fragmentation. This included the most prevalent daughter ion of 80 mass units. The derivatized fatty alcohol hexadecanol-TMS eluted at 10.29 minutes and the parent ion of 313 could be observed. The most prevalent ion was the M-14 ion of 299 mass units.
Quantification was carried out by injecting various concentrations of the appropriate authentic references using the GC/MS method described above. This information was used to generate a standard curve with response (total integrated ion count) versus concentration.
While specific examples of the subject inventions are explicitly disclosed herein, the above specification and examples herein are illustrative and not restrictive. Many variations of the inventions will become apparent to those skilled in the art upon review of this specification including the examples. The full scope of the inventions should be determined by reference to the examples, along with their full scope of equivalents, and the specification, along with such variations.
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Patent applications by Jay D. Keasling, Berkeley, CA US
Patent applications by LS9, INC.
Patent applications in class The single bonded oxygen is bonded directly to an additional carbon, which carbon may be single bonded to any element but may be multiple bonded only to carbon (i.e., carboxylic acid esters)
Patent applications in all subclasses The single bonded oxygen is bonded directly to an additional carbon, which carbon may be single bonded to any element but may be multiple bonded only to carbon (i.e., carboxylic acid esters)
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