Response-Surface-Optimized and Scaled-Up Microbial Electrosynthesis of Chiral Alcohols

A variety of enzymes can be easily incorporated and overexpressed within Escherichia coli cells by plasmids, making it an ideal chassis for bioelectrosynthesis. It has recently been demonstrated that microbial electrosynthesis (MES) of chiral alcohols is possible by using genetically modified E. coli with plasmid-incorporated and overexpressed enzymes and methyl viologen as mediator for electron transfer. This model system, using NADPH-dependent alcohol dehydrogenase from Lactobacillus brevis to convert acetophenone into (R)-1-phenylethanol, is assessed by using a design of experiment (DoE) approach. Process optimization is achieved with a 2.4-fold increased yield of 94±7 %, a 3.9-fold increased reaction rate of 324±67 μm h^-1 , and a coulombic efficiency of up to 68±7 %, while maintaining an excellent enantioselectivity of >99 %. Subsequent scale-up to 1 L by using electrobioreactors under batch and fed-batch conditions increases the titer of (R)-1-phenylethanol to 12.8±2.0 mm and paves the way to further develop E. coli into a universal chassis for MES in a standard biotechnological process environment.