Methyl-reducing methanogenesis by a thermophilic culture of Korarchaeia.

Methanogenesis mediated by archaea is the major source of methane, a strong greenhouse gas, and thus is critical for understanding Earth's climate dynamics. Recently, genes encoding diverse methanogenesis pathways were discovered in metagenome-assembled genomes affiliated with multiple archaeal phyla 1-7 . However, all experimental studies on methanogens are currently restricted to cultured representatives of the Euryarchaeota. Here we show for the first time methanogenic growth by a member of the lineage Korarchaeia within the phylum Thermoproteota (TACK superphylum) 5-7 . Following enrichment cultivation of Candidatus Methanodesulfokora washburnenis strain LCB3 we used measurements of metabolic activity and isotope tracer conversion to demonstrate methanol reduction to methane using hydrogen as electron donor. Analysis of the archaeon's circular genome and transcriptome revealed unique modifications in the energy conservation pathways linked to methanogenesis, including enzyme complexes involved in hydrogen and sulfur metabolism. The cultivation and characterization of this novel group of archaea is critical for a deeper evaluation of the diversity, physiology, and biochemistry of methanogens.