Marine cold seeps are unique chemosynthetic habitats fuelled by deeply sourced hydrocarbon‐rich fluids discharged at the seafloor. Through oxidizing methane and other hydrocarbons, microorganisms inhabiting cold seeps supply subsurface‐derived energy to higher trophic levels, sustaining highly productive oases of life in the deep sea. Despite the central role of microbiota in mediating biogeochemical cycles, the factors that g...

Summary Methyl‐coenzyme M reductase (MCR) has been originally identified to catalyse the final step of the methanogenesis pathway. About 20 years ago an aerobic me thane‐oxidizing archaea (ANME) were discovered that use MCR enzymes to activate methane. ANME thrive at the thermodynamic limit of life, are slow‐growing, and in most cases form syntrophic consortia with sulfate‐reducing bacteria. Recently, archaea that have the abi...

Summary Extraction of natural gas from unconventional hydrocarbon reservoirs by hydraulic fracturing raises concerns about methane migration into groundwater. Microbial methane oxidation can be a significant methane sink. Here, we inoculated replicated, sand‐packed, continuous mesocosms with groundwater from a field methane release experiment. The mesocosms experienced thirty‐five weeks of dynamic methane, oxygen and nitrate c...

Summary For the anaerobic remineralization of organic matter in marine sediments, sulfate reduction coupled to fermentation plays a key role. Here, we enriched sulfate‐reducing/fermentative communities from intertidal sediments under defined conditions in continuous culture. We transiently exposed the cultures to oxygen or nitrate twice daily and investigated the community response. Chemical measurements, provisional genomes a...