Stordalen mire environmental genomics Metagenome. permafrost metagenome

Permafrost environments are major carbon reservoirs undergoing dramatic changes as a result of increasing global temperatures. Thawing promotes microbial degradation of cryo-sequestered and new carbon leading to the biogenic production of methane, creating a positive feedback to climate change. The microbial communities responsible for this methane production remain largely unstudied. Here we use a combination of culture-independent molecular techniques and biogeochemistry to determine microbial community composition and function, and methane fluxes along a permafrost thaw gradient in northern Sweden. Methanogenic populations in partially thawed sites (Sphagnum-dominated bogs) were frequently dominated by a single phylotype, ‘Candidatus Methanoflorens stordalenmirensis’ gen. nov. sp. nov., belonging to the uncultivated lineage “RC-II”, which comprised up to 98% of the archaeal community. Metagenomic sequencing of a bog sample enriched in this population led to the recovery of its near-complete genome, revealing the genes necessary for hydrogenotrophic methanogenesis. Metaproteomics indicated that this archaeon is active in situ and highly expresses its methanogenesis proteins. Methane carbon isotope data are consistent with hydrogenotrophic production of methane in the partially thawed site. In addition to permafrost wetlands, the RC-II lineage (Candidatus Methanoflorentaceae fam. nov.) is widespread in high methane-flux habitats including peatlands, freshwater sediments and rice-paddies, suggesting that this lineage is both prevalent and a major contributor to global methane production. In thawing permafrost, ‘M. stordalenmirensis’ appears to be a key mediator of methane-based positive feedback to climate warming.