Iron oxide-mediated enhancement of extracellular electron transfer and symbiosis in consortium of electroactive bacteria and microalgae for wastewater treatment

This study explores the role of α-Fe₂O₃ in improving extracellular electron transfer (EET) and symbiotic interactions between electroactive Shewanella oneidensis MR-1, its gene-deficient mutants (Δ mtrC , Δ omcA , and Δ cymA ), and microalgae ( Chlorella vulgaris ). The iron oxide facilitates the efficient transfer of electrons generated by MR-1 to microalgal photosystem via the pathway of CymA-MtrC-OmcA to α-Fe₂O₃. This process enhances the removals of TOC, TN, and NH₄⁺-N in the MR-1 bacterial-algal consortium by 9.99%, 12.32%, and 52.25% respectively via OmcA regulation while boosting phosphorus removal by 16.27% through CymA regulation. The consortium exhibits 26.76% lower CO₂ emission and 62.93% higher biomass productivity. When integrated into microbial fuel cells with Δ cymA mutants, α-Fe₂O₃ elevates open-circuit voltage by 283.33%, confirming its ability to compensate for electron deficiencies caused by CymA defects. α-Fe₂O₃ enhances energy metabolisms (TCA cycle, quinone pool, and photosynthesis) to modulate the key metabolites including starch/sucrose, glycolysis, amino acids, lipids, and quorum sensing. These adaptations strengthen the symbiotic interactions and utilization of MR-1 bacterial-algal consortium for carbon and nutrients. Reactor experiments validate that α-Fe₂O₃ integration with the consortium achieves 93.43% COD removal and 55.99% NH₄⁺-N removal, while reducing N₂O emissions by 61.37%. The results reveal the interplay between OmcA, CymA, and iron oxides in optimizing bacterial-algal consortia and underscore the molecular mechanisms underlying iron oxide-enhanced EET for developing low-carbon, resource-efficient wastewater treatment.