Re-engineered β-oxidation reversal for the synthesis of ω-fuctionalized carboxylic acids in Escherichia coli

β-oxidation reversal is a novel carbon-chain elongation platform with high carbon and energy efficiencies that has been exploited to synthesize fatty acids and alcohols with varying chain lengths. While these products include industrially important fuels and chemicals, product diversity has been limited by the use of alkyl-CoAs, typically acetyl-CoA, as the primer. In order to expand the product range outside of those with a methyl group at the omega carbon, this study focused on the use of primers with varying ω-functional groups.  Product diversification was achieved through the utilization of ω-carboxylated succinyl-CoA and glutaryl-CoA as novel primers, in combination with iterative operation of carbon-chain elongation and usage of different pathway termination reactions at different β-functionalized intermediates. This expanded the product range of β-oxidation reversal to various ω-fuctionalized carboxylic acids such as α,ω-dicarboxylic acids, ω-1-keto fatty acids and ω-hydroxy fatty acids in Escherichia coli. Among all the products, adipic acid, a top industrial chemical as the monomer of nylon-6,6, showed 2.71 g/L of maximum titer. This re-designed reverse β-oxidation platform can be potentially used for the production of other important fuels and chemicals with diverse functionalities and applications.