Biological Upgrading of Organic Acids to Esters

Lignocellulosic biomass processing produces a plethora of molecules including carboxylic and aromatic acids which make up the carboxylate and arylate platforms, respectively.  The carboxylate and arylate platforms are typically comprised of C2-C6 carboxylic acids and aromatic acids, respectively, and can be derived from anaerobic digestion, dilute acid pretreatment, and/or hydrothermal pretreatment.  These platforms can be seen as both invaluable and inhibitory for microbial biocatalysts, and have great potential as targets for commercial biological up-grading to high-value products.  In this study, we developed a general framework for biological upgrading of organic acids to esters by assembling a designed modular cell and acid-to-ester production modules in a plug-and-play fashion.  Each module consists of an acyl transferase for conversion of acids to acyl CoAs, an alcohol/aldehyde dehydrogenase for conversion of acyl CoAs to alcohols, and an alcohol acyl transferase for ester biosynthesis by condensing alcohols and acyl CoAs. The developed framework enabled expansion of the ester platform produced, in vivo characterization of alcohol acyl transferases (AATs) for their novel activities  as well as use of single and/or mixed microbial consortia for synthesis of designer bioesters from organic acids.