Desulfurococcus kamchatkensis sp. nov., a novel hyperthermophilic protein-degrading archaeon isolated from a Kamchatka hot spring

A novel obligately anaerobic, hyperthermophilic, organotrophic archaeon, designated strain 1221n^T, was isolated from a hot spring of Uzon Caldera (Kamchatka Peninsula, Russia). Cells of strain 1221n^T were non-motile regular cocci, 0.6-1 μm in diameter. The temperature range for growth at pH 6.5 was 65-87 °C, with an optimum at 85 °C. The pH range for growth at 85 °C was 5.5-7.5, with an optimum at pH 6.5. Growth was not observed at or below 60°C or at or above 90 °C, as well as at or below pH 5.0 and at or above pH 8.0. The isolate fermented a wide range of substrates including proteins: α-keratin, albumin and gelatin. Elemental sulfur was not essential for growth, but stimulated growth. Strain 1221n^T synthesized 40 and 120 kDa proteinases localized on the cell envelope. The G+C content of the DNA was 44.4 mol%. Phylogenetic analysis based on 16S rRNA gene sequence comparison indicated that strain 1221n^T was affiliated with the genus Desulfurococcus. The level of 16S rRNA gene sequence similarity with other Desulfurococcus species was 96.7-98.1%, and Desulfurococcus amylolyticus was found to be the most closely related organism. Based on the data from the phylogenetic analysis and the physiological properties of the novel isolate, strain 1221n^T should be classified as representing a novel species, for which the name Desulfurococcus kamchatkensis sp. nov. is proposed. The type strain is 1221n^T (=DSM 18924^T=VKM B-2413^T).