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Fervidicoccus fontis gen. nov., sp. nov., a novel anaerobic thermophilic crenarchaeote from hot springs in Kamchatka, and proposal of Fervidicoccaceae fam. nov. and Fervidicoccales ord. nov.

¹ Winogradsky Institute of Microbiology, RAS;
² University of Bremen, Bremen;
³ Russian Academy of Sciences, Moscow

⁴ E-mail: annprv{at}gmail.com

Two novel thermophilic and slightly acidophilic strains, Kam940T and Kam1507b, with a 99% 16S rRNA gene sequence identity, were isolated from terrestrial hot springs of the Uzon Caldera, Kamchatka Peninsula. Cells of both strains were nonmotile regular cocci. Growth was observed between 55 and 85°C, with an optimum at 65-70°C (doubling time, 6.1 h) and pH values from 4.5 to 7.5, with an optimum at 5.5-6.0. The isolates were strictly anaerobic organotrophs and grew on a narrow spectrum of energy-rich substrates, such as beef extract, gelatin, peptone, pyruvate, rhamnose, starch, sucrose, yeast extract, with cell yield above 107 cells ml^-1. Elemental sulfur, sulfate, sulfite, thiosulfate and nitrate added as potential electron acceptors did not stimulate growth when tested with peptone. H2 at 100% in the gas phase inhibited growth on peptone. Glycerol dibiphytanyl glycerol tetraethers (GDGTs) with zero to four cyclopentyl rings were present in the lipid fraction of isolate Kam940T. The G+C content of the genomic DNA of the strain Kam940T was 37 mol%. Phylogenetic analysis based on 16S rRNA gene sequences indicated that the isolates were archaea of the Crenarchaeota phylum: only distantly related to the cultured members of the class Thermoprotei (no more than 89% identity) and formed an independent lineage adjacent to the orders Desulfurococcales and Acidilobales and clustering only with uncultured clones from hot springs of Yellowstone National Park and Iceland as the closest relatives. On the basis of its phylogenetic position and new phenotypic features, the isolates Kam940T (= DSM 19380T =VKM B-2539T) and Kam1507b are proposed to be assigned to a new genus and species Fervidicoccus fontis. The phylogenetic data as well as phenotypic properties suggest that the new crenarchaeotes form the basis of a novel family Fervidicoccaceae and a novel order Fervidicoccales within the class Thermoprotei.