Hydrogenotrophic methanogenesis in archaeal phylum Verstraetearchaeota reveals the shared ancestry of all methanogens
Methanogenic archaea are major contributors to the global carbon cycle and were long thought to belong exclusively to the euryarchaeotal phylum. Discovery of the methanogenesis gene cluster methyl-coenzyme M reductase (Mcr) in the Bathyarchaeota and thereafter the Verstraetearchaeota led to a paradigm shift, pushing back the evolutionary origin of methanogenesis to pre-date that of the Euryarchaeota. The methylotrophic methanogenesis found in the non-Euryarchaota distinguished itself from the predominantly hydrogenotrophic methanogens found in euryarchaeal orders as the former do not couple methanogenesis to carbon fixation through the reductive acetyl-coenzyme A (Wood-Ljungdahl) pathway, which was interpreted as evidence for independent evolution of the two methanogenesis pathways. Here, we report the discovery of a complete and divergent hydrogenotrophic methanogenesis pathway in a novel, thermophilic order of the Verstraetearchaeota which we have named Candidatus Methanohydrogenales, as well as the presence of the Wood-Ljungdahl pathway in the crenarchaeal order Desulfurococcales. Our findings support the ancient origin of hydrogenotrophic methanogenesis, suggest that methylotrophic methanogenesis might be a later adaptation of specific orders, and provide insight into how transition from hydrogenotrophic to methylotrophic methanogenesis might occur.