(576f) Engineering Biosynthesis of Medium-Chain Esters in Escherichia coli

Medium-chain esters such as isobutyl acetate and isoamyl acetate are high-volume chemicals with extensive applications in coating, solvent, flavor, and fragrance industries. However, the direct synthesis of these chemicals from glucose has not been well explored. In this work, we designed and engineered synthetic metabolic pathways in E. coli to enable such biosynthesis. Our pathways utilized amino acid biosynthesis and the Ehrlich pathway to supply precursors. Then alcohol acyltransferases from various organisms were investigated on their ability to catalyze the esterification reaction. It was discovered that ATF1 from Saccharomyces cerevisiae was the best enzyme for the formation of both isobutyl acetate and isoamyl acetate. The best isobutyl acetate producing strain was used for scale-up fermentation in a 1.3 L bioreactor and 36 g/L of IBAc was produced after 72 hours. We also applied this strategy to produce other esters such as isobutyl isobutyrate and isoamyl isovalerate and demonstrated protein engineering could be used to improve the pathway efficiency. This work demonstrates the feasibility of total biosynthesis of medium-chain esters as renewable chemicals.