Genomic inference of the metabolism of cosmopolitan subsurface Archaea, Hadesarchaea

The subsurface biosphere is largely unexplored and contains a broad diversity of uncultured microbes 1 . Despite being one of the few prokaryotic lineages that is cosmopolitan in both the terrestrial and marine subsurface 2 – 4 , the physiological and ecological roles of SAGMEG (South-African Gold Mine Miscellaneous Euryarchaeal Group) Archaea are unknown. Here, we report the metabolic capabilities of this enigmatic group as inferred from genomic reconstructions. Four high-quality (63–90% complete) genomes were obtained from White Oak River estuary and Yellowstone National Park hot spring sediment metagenomes. Phylogenomic analyses place SAGMEG Archaea as a deeply rooting sister clade of the Thermococci , leading us to propose the name Hadesarchaea for this new Archaeal class. With an estimated genome size of around 1.5 Mbp, the genomes of Hadesarchaea are distinctly streamlined, yet metabolically versatile. They share several physiological mechanisms with strict anaerobic Euryarchaeota. Several metabolic characteristics make them successful in the subsurface, including genes involved in CO and H 2 oxidation (or H 2 production), with potential coupling to nitrite reduction to ammonia (DNRA). This first glimpse into the metabolic capabilities of these cosmopolitan Archaea suggests they are mediating key geochemical processes and are specialized for survival in the subsurface biosphere. Genomic reconstruction from hot spring sediment metagenomes show that 'Hadesarchaea' have streamlined yet metabolically versatile genomes, with genes involved in CO and H 2 oxidation, with potential coupling to nitrite reduction to ammonia.