Thermogladius calderae gen. nov., sp. nov., an anaerobic, hyperthermophilic crenarchaeote from a Kamchatka hot spring

An obligately anaerobic, hyperthermophilic, organoheterotrophic archaeon, strain 1633^T, was isolated from a terrestrial hot spring of the Uzon Caldera (Kamchatka Peninsula, Russia). Cells were regular cocci, 0.5–0.9 μm in diameter, with one flagellum. The temperature range for growth was 80–95 °C, with an optimum at 84 °C. Strain 1633^T grew on yeast extract, beef extract, peptone, cellulose and cellobiose. No growth was detected on other sugars or carbohydrates, organic acids, or under autotrophic conditions. The only detected growth products were CO₀, acetate, and H₂. The growth rate was stimulated by elemental sulfur, which was reduced to hydrogen sulfide. The in silico-calculated G+C content of the genomic DNA of strain 1633^T was 55.64 mol%. 16S rRNA gene sequence analysis placed strain 1633^T together with the non-validly published ‘Thermogladius shockii’ strain WB1 in a separate genus-level cluster within the family Desulfurococcaceae. Average nucleotide identity (ANI) results revealed 75.72% identity between strain 1633^T and ‘Thermogladius shockii’ WB1. Based on these results we propose a novel genus and species with the name Thermogladius calderae gen. nov., sp. nov. The type strain of the type species is 1633^T (=DSM 22663^T=VKM B-2946^T).