Extracellular electron transfer drives efficient H2-independent methylotrophic methanogenesis by Methanomassiliicoccus, a seventh order methanogen

Methylotrophic methanogenesis is achieved via methyl group dismutation or H 2 reduction. This study reports extracellular electron droving efficient methylotrophic methanogenesis. The 7 th order methanogen Methanomassiliicoccus luminyensis exclusively implements H 2 -dependent methylotrophic methanogenesis, but strain CZDD1 isolated from paddy soil possessed a higher methane-producing rate in coculture with Clostridium malenominatum CZB5 or the electrogenic Geobacter metallireducens. Chronoamperometry detected current production from CZB5, and current consumption accompanied CH 4 production in a methanol-containing electrochemical culture of CZDD1. This demonstrated that M. luminyensis was capable of both direct species electron transfer (DIET) and extracellular electron transfer (EET) in methylotrophic methanogenesis. EET and DIET also enabled CZDD1 to produce methane from dimethyl arsenate. Differential transcriptomic analysis on H 2 -versus EET- and DIET-cocultures suggested that a membrane-bound Fpo-like complex and archaella of M. luminyensis CZDD1 could accept extracellular electrons. Given the ubiquitous environmental distribution of Methanomassiliicoccus strains, EET driven methylotrophic methanogenesis may contribute significantly to methane emission.