Periplasmic FeS Electron Conduits: Tuning Electrocoupling and Respiratory Dehalogenation in a Synthetic Consortium

Electron delivery within and between bacterial cells is a central bottleneck in anaerobic biotransformation of electron acceptor‐type substrates (EATS). Using hexabromocyclododecane (HBCD) as a model organohalogen, we developed a cysteine desulfhydrase (CSD)‐associated periplasmic FeS biomineralization strategy in a defined synthetic consortium. CSD‐associated FeS formation enabled rapid installation of FeS conduits in non‐sulfate‐reducing bacteria within ∼3 h, forming predominantly periplasmic conductive interfaces that lowered interfacial charge‐transfer resistance and increased capacitive electron storage. Electrochemical analyses revealed coculture‐specific electron‐transfer behavior, increased electron‐accepting capacity, and enhanced transport activity; cocultures outperformed monocultures, consistent with strengthened interspecies electron transfer. Detection of lower‐brominated intermediates and bromide release supported dihaloelimination‐dominated debromination, with Fe‐matched cell‐free FeS accounting for only 2.8% of the live‐cell Br − signal. Inhibitor profiling further suggested that FeS alters electron‐transfer behavior from NADH/menaquinone‐linked steps toward terminal reductive processes, consistent with relief of respiratory bottlenecks. Structure prediction and docking support a working model in which a QueG‐like, cobalamin‐dependent candidate terminal reductase may participate in HBCD reduction, while FeS conduits enhance local electron delivery, charge‐transfer behavior, and whole‐cell debromination. Overall, periplasmic FeS conduits provide a CSD‐associated interfacial strategy to modulate electron flux in this defined coculture, highlighting a potentially transferable route for transforming emerging organohalogens and other EATS.