Abstract
A hyperthemophilic member of the Nanoarchaeota from Obsidian Pool, a thermal feature in Yellowstone National Park was characterized using single cell isolation and sequencing, together with its putative host, a Sulfolobales archaeon. This first representative of a non-marine Nanoarchaeota (Nst1) resembles Nanoarchaeum equitans by lacking most biosynthetic capabilities, the two forming a deep-branching archaeal lineage. However, the Nst1 genome is over 20% larger, encodes a complete gluconeogenesis pathway and a full complement of archaeal flagellum proteins. Comparison of the two genomes suggests that the marine and terrestrial Nanoarchaeota lineages share a common ancestor that was already a symbiont of another archaeon. With a larger genome, a smaller repertoire of split protein encoding genes and no split non-contiguous tRNAs, Nst1 appears to have experienced less severe genome reduction than N. equitans. The inferred host of Nst1 is potentially autotrophic, with a streamlined genome and simplified central and energetic metabolism as compared to other Sulfolobales. The two distinct Nanoarchaeota-host genomic data sets offer insights into the evolution of archaeal symbiosis and parasitism and will further enable studies of the cellular and molecular mechanisms of these relationships.
