Microbial Production of Short-Chain Alkanes

Microbial production of short-chain alkanes

So Young Choi, Yong Jun Choi and Sang Yup Lee

Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technology

(KAIST), Daejeon, South Korea

Our increasing concerns on limited fossil fuels and global environmental problems are urging us to develop sustainable biofuels from renewable resources. Although microbial production of diesel has been reported, production of another much demanded transport fuel, gasoline, has not yet been demonstrated. Here we report the development of platform Escherichia coli strains that are capable of producing short chain alkanes (gasoline), free fatty acids (FFAs), fatty esters, and fatty alcohols through the fatty acyl-[acyl carrier protein (ACP)] to fatty acid to fatty acyl-CoA pathway. The β-oxidation pathway was blocked by deleting the fadE gene to prevent the degradation of fatty acyl-CoAs generated in vivo and the activity of 3-oxoacyl- ACP synthase (FabH), which is inhibited by unsaturated fatty acyl-ACPs, was enhanced to promote the initiation of fatty acid biosynthesis by deleting the fadR gene. A modified thioesterase was employed to convert short chain fatty acyl-ACPs to the corresponding FFAs, which were consequently converted to short chain alkanes by the sequential reactions of E. coli fatty acyl-CoA synthetase, Clostridium acetobutylicum fatty acyl-CoA reductase and Arabidopsis thaliana fatty aldehyde decarbonylase. The final engineered strain produced up
to 580.8 mg l-1 of SCAs consisting of nonane (327.8 mg l-1), dodecane (136.5 mg l-1),
tridecane (64.8 mg l-1), 2-methyl-dodecane (42.8 mg l-1) and tetradecane (8.9 mg l-1) together with small amounts of other hydrocarbons. [This work was supported by the Advanced Biomass Research and Development Center of Korea (ABC-2010-0029799) through the Global Frontier Research Program of the Ministry of Science, ICT and Future Planning (MSIP) through the National Research Foundation (NRF). Systems metabolic engineering work was supported by the Technology Development Program to Solve Climate Changes on Systems Metabolic Engineering for Biorefineries (NRF-2012-C1AAA001-
2012M1A2A2026556) by MSIP through NRF].