Homoacetogenic Consortia from BioH ₂ Reactors Enable CO ₂ Bioconversion in Microbial Electrosynthesis

Microbial electrosynthesis (MES) systems rely on the ability of microorganisms to form biofilms capable of capturing electrons directly from solid electrodes via extracellular electron transfer (EET) mechanisms. In this study, the feasibility of using acetogenic consortia derived from biohydrogen (BioH2) reactors as an inoculum for MES was investigated. The consortium was obtained from the natural fermentation of sugarcane molasses in a mesophilic anaerobic reactor and subsequently applied to a single-chamber MES cell operated at −1.0 V (vs Ag/AgCl) and 35 °C. The inoculum demonstrated high adaptability to bioelectrochemical conditions, resulting in the formation of electroactive biofilms and efficient CO2 bioconversion. The system reached a maximum acetic acid concentration of 1.88 g L–1, along with the production of other volatile fatty acids (VFAs), including butyrate, propionate, and isobutyrate, suggesting the activation of complementary metabolic pathways, such as reverse β-oxidation. Coulombic efficiency peaked at 60.4% during enriched phases, and current density was positively correlated with VFA accumulation. Microbial community analysis revealed the predominance of homoacetogenic and electroactive genera such as Acetobacterium, Clostridium, Desulfovibrio, and Sporomusa. These findings demonstrate that fermentative consortia from BioH2 reactors represent a promising, naturally enriched microbial source for MES applications, enabling the conversion of CO2 into valuable chemicals with minimal pretreatment.