Cultivation and visualization of a methanogen of the phylum Thermoproteota

Methane is the second most abundant climate-active gas and understanding its sources and sinks is a crucial endeavor in microbiology, biogeochemistry, and climate sciences (1,2). For decades, it was thought that methanogenesis, the ability to conserve energy coupled to methane production, was restricted to a taxonomically and metabolically specialized group of archaea, the Euryarchaeota1. The discovery of marker genes for anaerobic alkane cycling in metagenome-assembled genomes obtained from diverse habitats has led to the hypothesis that archaeal lineages outside the Euryarchaeota are involved in methanogenesis (3-6). Here, we cultured Candidatus Methanosuratincola yellowstonensis, a member of the archaeal phylum Thermoproteota, from a terrestrial hot spring. Growth experiments combined with activity assays, stable isotope tracing, and genomic analyses confirmed that this thermophilic archaeon grows via methyl-reducing hydrogenotrophic methanogenesis. Cryo-electron tomography revealed that Ca. M. yellowstonensis cells are archaellated coccoid cells that form intercellular bridges, providing two to three cells with a continuous cytoplasm and S-layer. The wide environmental distribution of Ca. M. yellowstonensis suggests that they might play important and hitherto overlooked roles in carbon cycling within diverse anoxic habitats.