Microbial upgrading of lignin-derived carboxylates to branched-chain esters for Fermentable sugars drop-in biofuels modular cell extracellular extractive organic cytosol aqueous phase phase alsS ilvC ilvD kivd adh pyruvate isobutanol adh adh acetaldehyde ethanol aat isobutyl acylate aat Background acetyl-CoA acetate ethyl acylate pct adh aat • Volatile organic acids are low-value byproducts of acid acyl-CoA acyl alcohol acyl acylate fermentative metabolism such as anaerobic digestion of aat aat lignocellulosic biomass or organic wastes. O isobutyl acetate ethyl acetate acyl acetate • Esters are valuable as drop-in biofuels or as flavor and O Propionate fragrance bioproducts. ester Isobutyl Propionate Pentanoate ester platform O platform Approach O O O Propyl Propionate • By employing the modular cell engineering approach, a O Pentyl Pentanoate O O general framework was devised for upgrading volatile organic Acetate ester Ethyl Propionate platform O acids to high-value linear and branched chain esters. O O Isobutyl Pentanoate Butyl Acetate Outcome O O O • A general framework for microbial biosynthesis of linear and O O O Ethyl Pentanoate Propyl Acetate Hexyl Acetate branched-chain ester platforms was proven in E. coli. O O • Successfully, biologically, upgraded 5 carboxylates to 16 out O O Pentyl Acetate of a total of 18 potential esters. Hexanoate ester O Isobutyl Acetate platform O • Characterized in vivo alcohol acyltransferases for linear and O Ethyl Acetate branched-chain ester biosynthesis. O Ethyl Hexanoate O • These targeted esters are discussed as potential fuels beyond O O Ethyl Butyrate flavor, fragrant, and solvent applications. O O Hexyl Hexanoate Butyrate ester platform Significance O O O • An innovative biological conversion route was developed for Isobutyl Butyrate O conversion of lignocellulosic biomass or organic wastes into O Isobutyl Hexanoate biofuels and high-value chemicals. Butyl Butyrate 1 Layton, D.S., Trinh, C.T., 2016. “Microbial Synthesis of a Branched-Chain Ester Platform from Organic Waste Carboxylates,” Metab Eng Comm, in press. doi:10.1016/j.meteno.2016.08.001 .