Physiological and Genomic Characterization of a Hyperthermophilic Archaeon sp. nov. Isolated From a Deep-Sea Hydrothermal Vent Warrants the Reclassification of the Genus .

Hyperthermophilic archaea of the genus are the subject of many fundamental and biotechnological researches. Despite their significance, the class is currently represented by only eight species obtained as axenic cultures and taxonomically characterized. Here, we report the isolation and characterization of a new species of from a deep-sea hydrothermal vent (Mid-Atlantic Ridge, TAG) for which the name sp. nov. is proposed. The type strain is SE56 (=DSM 110954 = VKM B-3474). The cells of the novel isolate are motile irregular cocci growing at 50-85°C, pH 5.5-7.5, and NaCl concentrations of 1.5-4.5% (w/v). Strain SE56 grows lithoautotrophically with H as an electron donor, sulfite or thiosulfate as an electron acceptor, and CO/HCO as a carbon source. It is also capable of chemoorganotrophic growth by reduction of sulfate, sulfite, or thiosulfate. The genome of the new isolate consists of a 2,115,826 bp chromosome with an overall G + C content of 46.0 mol%. The whole-genome annotation confirms the key metabolic features of the novel isolate demonstrated experimentally. Genome contains a complete set of genes involved in CO fixation reductive acetyl-CoA pathway, gluconeogenesis, hydrogen and fatty acids oxidation, sulfate reduction, and flagellar motility. The phylogenomic reconstruction based on 122 conserved single-copy archaeal proteins supported by average nucleotide identity (ANI), average amino acid identity (AAI), and alignment fraction (AF) values, indicates a polyphyletic origin of the species currently included into the genus , warranting its reclassification.