Short-chain esters of organic acids such as ethyl lactate and ethyl acetate are valuable feedstocks for biofuels and chemicals. An advent of environmental safety policies and development of sustainable industrialization practices encouraged researchers for microbial synthesis of short-chain esters. Microbial short-chain esters production by an engineered Escherichia coli is afflicted by both low titer and low selectivity. In this work, we have constructed engineered E. coli to produce ethyl lactate and ethyl acetate from renewable substrates. As the first step, seven enzymes were selected by bioprospecting of ester producing enzymes: diacylglycerol-transferase, ethanol-o-acyltransferase, acetylxylan-esterase, carbohydrate-esterase; acyl-coenzymeA:ethanol O-acyltransferase, ethyl-ester-synthase-1; and esterase-A. Then, in vitro assays were conducted to identify the optimal pH and temperature for these novel enzymes. Recombinant E. coli strains were constructed by expressing the esterase and acyl-alcohol transferase in E. coli strains engineered for overproducing ethanol and lactic acid. High-cell density fermentations were conducted under anaerobic conditions and the strain expressing esterase-A produced the highest ethyl lactate (10.3 ±0.5 mg/L) and ethyl acetate (81.6 ±4.5 mg/L) from glucose as a carbon source. The result shows that our proposed approach may open a new avenue in biotechnology for the production of short-chain esters in E. coli. Further work is underway, to increase the production rate and titer.

Engineered production of lactate and acetate short-chain esters in Escherichia coli

ACS Spring Meeting 2021

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