Microbial Anode-Driven Electro-Fermentation for Succinate Production

This study demonstrates a proof-of-concept microbial electrochemical system (MES) that integrates a Geobacter sulfurreducens anodic biofilm with Actinobacillus succinogenes cathodic electro-fermentation. The anode, poised at 0 V versus Ag/AgCl, supported extracellular electron transfer from acetate oxidation, yielding a coulombic efficiency of up to 72.9%. When the cathode was switched from an abiotic ferricyanide sink to A. succinogenes medium containing neutral red, current increased sharply, reflecting mediator-assisted electron transfer. Cathodic metabolism showed a redirection in flux: succinate selectivity improved by 9.9%, increasing from 42.9% to 52.8% of input carbon, while formate and acetate decreased by 7.8% and 3.0%, respectively, without loss in overall carbon recovery. This improvement in succinate selectivity is industrially relevant in that it not only increases succinate yield but also lowers separation costs due to lower byproducts (formate and acetate). These results reveal that a poised G. sulfurreducens anode can sustain sufficient current to influence A. succinogenes product distribution, supporting the feasibility of biologically integrated MES-electro-fermentation. Potential hydrogen evolution, which could possibly contribute to increased succinate selectivity, was a thermodynamic possibility rather than a confirmed pathway. Future work was proposed to resolve electron partitioning, mediator kinetics, and cross-feeding interactions.