NanoFeO as Solid Electron Shuttles to Accelerate Acetotrophic Methanogenesis by .

Magnetite nanoparticles (nanoFeO) have been reported to facilitate direct interspecies electron transfer (DIET) between syntrophic bacteria and methanogens thereby improving syntrophic methanogenesis. However, whether or how nanoFeO affects acetotrophic methanogenesis remain unknown. Herein, we demonstrate the unique role of nanoFeO in accelerating methane production from direct acetotrophic methanogenesis in -enriched cultures, which was further confirmed by pure cultures of Compared with other nanomaterials of higher electrical conductivity such as carbon nanotubes and graphite, nanoFeO with mixed valence Fe(II) and Fe(III) had the most significant stimulatory effect on methane production, suggesting its redox activity rather than electrical conductivity led to enhanced methanogenesis by . Cell morphology and spectroscopy analysis revealed that nanoFeO penetrated into the cell membrane and cytoplasm of . These results provide the unprecedented possibility that nanoFeO in the cell membrane of methanogens serve as electron shuttles to facilitate intracellular electron transfer and thus enhance methane production. This work has important implications not only for understanding the mechanisms of mineral-methanogen interaction but also for optimizing engineered methanogenic processes.