Synthetic bacterial consortium enhances hydrogen production in microbial electrolysis cells and anaerobic fermentation

[Display omitted] •Syntrophic interactions enhance H2-ethanol co-production by MECs and fermentation.•The defined co-cultures enhanced substrate conversion efficiency for H2 production.•Co-cultures interactions include cross-feeding and interspecies electron transfer.•Geobacter regulates metabolic intermediates of Ethanoligenens in co-cultures.•Co-cultures forms dense constructions with intercellular pili-like nanowires. Microbial electrolysis cells (MECs) provide effective approaches for hydrogen production from wastewater and renewable biomass. Improving the efficiency of energy recovery from wastes remains a challenge. Here we report the cross-feeding interactions between the hydrogen-producing Ethanoligenens harbinense and electroactive Geobacter sulfurreducens in MECs and anaerobic fermentation using glucose as electron donor. Results showed that G. sulfurreducens could oxidize acetate produced by E. harbinense and transfer electrons extracellularly to the electrode of MECs, which also enhanced hydrogen production by E. harbinense via mitigation of metabolic feedback inhibition and enhancement of interspecies electron transfer. The defined co-cultures showed 2.5–2.9 times higher hydrogen production rates compared to the mono-cultures, while the MECs further enhanced the substrate conversion efficiency and converted electrical energy into hydrogen energy. The molar ratio of ethanol to acetic acid in co-cultured MECs doubled compared to mono-cultures, indicating that G. sulfurreducens steered the fermentation products of E. harbinense towards ethanol. The co-cultures formed dense aggregates or biofilms, in which close physical interactions by intercellular pili-like nanowire structures were observed between E. harbinense and G. sulfurreducens in the co-culture biofilms of both anode and cathode. These findings provide new insight into syntrophic interactions, beyond that previously reported on fermentative hydrogen-producing bacteria with electroactive bacteria or methanogens, and offer an effective strategy to enhance H2 production and steer metabolic products of fermentative bacteria.