Engineering an electroactive Escherichia coli for the microbial electrosynthesis of succinate by increasing the intracellular FAD pool

Abstract

In this study, the FAD synthesis pathway was manipulated to increase its cellular concentration and thereby improve the electroactivity of E. coli. In a microbial electrosynthesis (MES) system with neutral red as electron carrier and fumarate as the sole electron acceptor, the engineered strains derived from three E. coli lines displayed increased electric current in the reaction system, indicating improved electroactivity. Furthermore, the production of succinate from fumarate increased by around 60% compared with that of the parent strains, confirming the improvement of E. coli electroactivity by manipulating the FAD synthesis pathway. An MES reaction was performed with engineered E. coli 8739, and an altered metabolic profile with more reductive fermentation products was obtained. When the electroactive succinate-producing strain E. coli T110 was used in the MES, a yield of 0.97 ± 0.02 mol/mol glucose was achieved, which corresponds to an approximately 1.4-fold increase compared with the fermentation with no electricity supply or non-electroactive T110. In addition, a carbon concentration mechanism (CCM) was employed to further improve succinate production and yield in the MES, which produced a succinate yield of 1.16 mol/mol glucose, a 1.7-fold increase compared with that of the parent strain T110, indicating that the electroactive E. coli could be used in MES to produce specific fermentation products with improved yield.