Cellular electron transfer in anaerobic photo-assisted biocathode microbial electrosynthesis systems for acetate production from inorganic carbon (HCO3–)

The crucial role played by the cellular electron transfer in the production of acetate from aqueous inorganic carbon (HCO3–, bicarbonate) in anaerobic photo-assisted microbial electrosynthesis (MES) biocathodes incorporating a WO3/MoO3/g-C3N4 Z-scheme heterojunction and either Serratia marcescens Q1 or Stenotrophomonas sp. JY6 electrotrophs is disclosed. The electron transfer inhibitor 2,4-dinitrophenol (DNP) diffusing through the bacterial cell membrane was used to alter the ratio of indirect (via H2) and direct extracellular electron transfer processes, resulting in lower physiological release of extracellular polymeric substances (EPS) and lower acetate production rates under a transitional period. DNP effectively cancelled the synergistic effects on acetate production produced by the photo-irradiation of the WO3/MoO3/g-C3N4 heterojunction biocathode. The physiological release of EPS with either a compositional diversity (Q1) or varying composition percentages (Q1 or JY6), was correlated to photo-irradiation and to the electrotrophic species, whereas the total amount of EPS was closely related with the electrotrophic DNP-based cellular electron transfer processes. Interestingly, the microorganisms adapted and overcame the impact of DNP after only 4 days of continuous operation and restored their normal physiological metabolism after 7.5 d operation with periodical replenishment of bicarbonate. This study provides a detailed theoretical basis to understand the impact of direct and indirect extracellular electron transfer in hybrid photo-assisted MES biocathodes and elucidates the behavior of non-photosynthetic electrotrophic bacteria favoring high conversion of aqueous inorganic carbon (HCO3–) to acetate.