A hyperthermophilic, strictly anaerobic archaeon, designated strain SY113T, 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 SY113T were performed at 85 °C at 0.1 MPa. Cells of strain SY113T 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 SY113T 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 SY113T 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 SY113T showed that the novel isolate belonged to the genus
Thermococcus
. On the basis of physiological characteristics, average nucleotide identity values and in silico DNA–DNA hybridization results, we propose a novel species, named Thermococcus aciditolerans sp. nov. The type strain is SY113T (=MCCC 1K04190T=JCM 39083T).
Microbial Community Structure of Deep-sea Hydrothermal Vents on the Ultraslow Spreading Southwest Indian Ridge