Modular Biosynthesis for the Production of Advanced Fuels and Chemicals

Advanced (long-chain) fuels and chemicals are generated from short-chain metabolic intermediates through pathways that require carbon-chain elongation. The condensation reactions mediating this carbon-carbon bond formation can be catalyzed by enzymes from the thiolase superfamily, including beta-ketoacyl-acyl-carrier protein (ACP) synthases, polyketide synthases, 3‐hydroxy-3-methylglutaryl-CoA synthases, and biosynthetic thiolases. Pathways involving these enzymes have been exploited for fuel and chemical production, with fatty acid biosynthesis (β‐ketoacyl‐ACP synthases) attracting the most attention in recent years. Degradative thiolases, which are part of the thiolase superfamily and naturally function in the b‐oxidation of fatty acids, can also operate in the synthetic direction and thus enable carbon-chain elongation. We have demonstrated that a functional reversal of the β-oxidation cycle can be engineered in Escherichia coli and used for the synthesis of alcohols and carboxylic acids of various chain lengths. The engineered reversal of the β‐oxidation cycle is composed of three core modules: i) priming, ii) elongation, and iii) termination. This modular nature allows the use of the engineered pathway as a general platform for the synthesis of a wide array of functional molecules with applications to fuel and chemical production.