Ecological and metabolic restructuring of anaerobic microbiomes under sulfate stress via magnetite-enhanced...

Anaerobic digestion systems with elevated sulfate often suffer reduced methane yields, challenged by the competition between sulfate-reducing bacteria and methanogens, and inhibited by hydrogen sulfide introduction. The present work explores the role of magnetite in improving anaerobic digestion performance under elevated sulfate conditions by chemically influencing the anaerobic system and reshaping microbial interaction patterns.

Magnetite addition mitigated hydrogen sulfide toxicity via precipitation and increased methane production by 19%. Genome-centric metagenomics revealed a notable proliferation of the methanogenic population in the magnetite-amended reactors, consistent with the elevated methane output in the presence of both magnetite and sulfate, without suppressing sulfate-reducing, homoacetogenic, or syntrophic acetate-oxidizing activity. Magnetite was associated with enhanced methanogenesis and a strengthened cooperative syntrophic network among the four microbial guilds, in line with more efficient carbon and electron flow despite sulfate stress. Community genome-scale metabolic modeling supported these trends, validating the feasibility of the proposed interaction network and indicating that interspecies metabolite transfer between partners is stoichiometrically feasible, supporting the observed community behavior.

This study demonstrates the role of magnetite not only as a hydrogen sulfide scavenger but also as a community modulator, promoting resilient direct electron transfer-based networks, ultimately unlocking higher-efficiency biogas production in sulfate-impacted digesters. Our findings support the concept that interactions between sulfate-reducers and hydrogenotrophic methanogens are not purely competitive, and that conductive materials such as magnetite can enhance their metabolic coupling even under sulfate stress. Video Abstract.