Regulating electron transfer in predominantly fermentative microbiomes has broad implications in environmental, chemical, food, and medical fields. Here we demonstrate electrochemical control in fermenting food waste, digestate, and wastewater to improve lactic acid production. We hypothesize that applying anodic potential will expedite and direct fermentation towards lactic acid. Continued operation that introduced epi/endophytic communities (Lactococcus, Lactobacillus, Weissella) to pure culture Lactiplantibacillus plantarum reactors with static electrodes was associated with the loss of anode-induced process intensification despite 80% L. plantarum retention. Employing fluidized electrodes discouraged biofilm formation and extended electrode influence to planktonic gram-positive fermenters using mediated extracellular electron transfer. While short-term experiments differentially enriched Lactococcus and Klebsiella spp., longer-term operations indicated convergent microbiomes and product spectra. These results highlight a functional resilience of environmental fermentative microbiomes to perturbations in redox potential, underscoring the need to better understand electrode induced polymicrobial interactions and physiological impacts to engineer tunable open-culture or synthetic consortia.

Microbial electrosynthesis (MES) converts CO₂ into value-added products such as volatile fatty acids (VFAs) with minimal energy use, but low production titer has limited scale-up and commercialization. Mediated electron transfer via H₂ on the MES cathode has shown a higher conversion rate than the direct biofilm-based approach, as it is tunable via cathode potential control and accelerates electrosynthesis from CO₂. Here we report high acetate titers can be achieved via improved in situ H₂ supply by nickel foam decorated carbon felt cathode in mixed community MES systems. Acetate concentration of 12.5 g L⁻¹ was observed in 14 days with nickel-carbon cathode at a poised potential of −0.89 V (vs. standard hydrogen electrode, SHE), which was much higher than cathodes using stainless steel (5.2 g L⁻¹) or carbon felt alone (1.7 g L⁻¹) with the same projected surface area. A higher acetate concentration of 16.0 g L⁻¹ in the cathode was achieved over long-term operation for 32 days, but crossover was observed in batch operation, as additional acetate (5.8 g L⁻¹) was also found in the abiotic anode chamber. We observed the low Faradaic efficiencies in acetate production, attributed to partial H₂ utilization for electrosynthesis. The selective acetate production with high titer demonstrated in this study shows the H₂-mediated electron transfer with common cathode materials carries good promise in MES development.