Expanding methanogens with genetic potential for extracellular electron transfer capabilities in anaerobic wastewater treatment ecosystems

Methanogens have key roles in wastewater treatment, coupling water quality control and bioenergy recovery. However, our understanding of direct interspecies electron transfer via extracellular electron transfer (EET)—a newly discovered methanogenic pathway for CO₂ reduction—remains limited because pure-culture cultivation is difficult and few strains are confirmed. Here we show that a survey of 378 methanogen genomes reveals key methanogenesis-related genes and widespread EET-associated structures, including proton-pumping Fpo complexes, conductive flagellin, conductive sheaths and multihaem c-type cytochromes. We identify 84 strains with genomic potential for EET, greatly expanding the candidate pool. Analysis of over 500 anaerobic digestion samples, including those from wastewater treatment systems, revealed that putative EET-capable methanogen genera are widespread, environmentally correlative and central to syntrophic networks. These findings deepen our understanding of methanogenic diversity in advancing wastewater treatment and sustainability while also broadening insights into methanogenesis across diverse aquatic ecosystems.