Beyond methanogenesis: expanding roles for methanogenic archaea.

As key players in anoxic environments, methanogenic archaea account for the vast majority of biogenic methane emissions and play important roles during organic matter mineralization. Growing evidence indicates potential for broader ecological roles beyond methanogenesis. This review summarizes the physiology of biogeochemically relevant transformations of iron minerals, humic acid, biochar, and toxic heavy metals/metalloids. We examine how methanogenic archaea couple carbon cycling with other element cycles through methanogenic pathways and electron transfer processes. We also discuss known and potential molecular mechanisms that underlie these interactions. Furthermore, we highlight the discovery of the reversal of methanogenesis driven by extracellular electron transfer and its potential for methane bioconversion technologies. This work underscores the physiological versatility of methanogenic archaea, suggesting their diverse roles in biogeochemical cycles.