Defined Electrosynthetic Microbial Consortia Reveal Electron Transfer Modes Governing Acetate Production

Precise manipulation of interspecies electron transfer (IET) is critical for advancing microbial electrosynthesis (MES) toward efficient CO₂ bioconversion. Here, defined synthetic consortia are constructed by pairing Shewanella oneidensis MR-1, a model bidirectional electroactive bacterium, with Clostridium aceticum (electroactive acetogen) or Acetobacterium woodii (nonelectroactive acetogen), mimicking functional guilds commonly observed in natural MES communities. Co-cultivation markedly boosts acetate production by up to 88%, achieving 1.16 ± 0.01 and 1.05 ± 0.01 g L^-1, with carbon conversion efficiencies exceeding 84%. Comprehensive electrochemical, spectroscopic, and biomass analyses reveal distinct spatial electron transfer modes: DIET via cytochrome c and riboflavin dominates at the biofilm-electrode interface in S. oneidensis-C. aceticum consortia, whereas S. oneidensis-A. woodii consortia prefer H₂/formate-mediated IET in the planktonic phase. This metabolic stratification enables S. oneidensis to function as an "ecosystem engineer," orchestrating electron flow to optimize CO₂-to-acetate conversion across biofilm and suspension niches. The proposed synthetic ecology strategy provides a blueprint for designing high-efficiency MES consortia, paving new avenues for sustainable carbon capture and bio-based chemical production.