sp. nov., a piezotolerant, hyperthermophilic archaeon isolated from a deep-sea hydrothermal vent chimney in the Southwest Indian Ridge.

A hyperthermophilic, strictly anaerobic archaeon, designated strain SY113, was isolated from a deep-sea hydrothermal vent chimney on the Southwest Indian Ridge at a water depth of 2770 m. Enrichment and isolation of strain SY113 were performed at 85 °C at 0.1 MPa. Cells of strain SY113 were irregular motile cocci with peritrichous flagella and generally 0.8-2.4 µm in diameter. Growth was observed at temperatures between 50 and 90 °C (optimum at 85 °C) and under hydrostatic pressures of 0.1-60 MPa (optimum, 27 MPa). Cells of SY113 grew at pH 4.0-9.0 (optimum, pH 5.5) and a NaCl concentration of 0.5-5.5 % (w/v; optimum concentration, 3.0 % NaCl). Strain SY113 was an anaerobic chemoorganoheterotroph and grew on complex proteinaceous substrates such as yeast extract and tryptone, as well as on maltose and starch. Elemental sulphur stimulated growth, but not obligatory for its growth. The G+C content of the genomic DNA was 55.0 mol%. Phylogenetic analysis of the 16S rRNA sequence of strain SY113 showed that the novel isolate belonged to the genus . On the basis of physiological characteristics, average nucleotide identity values and DNA-DNA hybridization results, we propose a novel species, named sp. nov. The type strain is SY113 (=MCCC 1K04190=JCM 39083).