A conditional piezophilic, hyperthermophilic archaeon showing growth over a wide range of temperature, pH and pressure was isolated from an oil-immersed hydrothermal chimney at a depth of 2006.9 m in the Guaymas Basin. Enrichment and isolation of strain A501T were performed at 80 °C at 0.1 MPa. Cells of isolate A501T were irregular motile cocci with a polar tuft of flagella and generally 0.6–2.6 µm in diameter. Growth was detected over the range 50–100 °C (optimal growth at 85 °C) at atmospheric pressure and was observed at 102 °C at a pressure of 10 MPa. At 85 °C, growth was observed at a pressure of 0.1–70 MPa (optimum pressure 0.1 MPa–30 MPa), while at 95 °C, the pressure allowing growth ranged from 0.1 MPa to 50 MPa (optimum pressure 10 MPa). Cells of strain A501T grew at pH 4–9 (optimum pH 7.0) and a NaCl concentration of 1.0–5.0 % (w/v) (optimum concentration 2.5 % NaCl). This isolate was an anaerobic chemo-organoheterotroph and was able to utilize yeast extract, peptone, tryptone and starch as the single carbon source for growth. Elemental sulfur and cysteine stimulated growth; however, these molecules were not necessary. The DNA G+C content of the complete genome was 53.47 mol%. The results of 16S rRNA gene sequence analysis indicated that strain A501T belongs to the genus Thermococcus . There was no significant similarity between strain A501T and the phylogenetically related species of the genus Thermococcus based on complete genome sequence alignments and calculation of the average nucleotide identity and the tetranucleotide signature frequency correlation coefficient. These results indicate that strain A501T represents a novel species, Thermococcus eurythermalis sp. nov. The type strain is A501T ( = CGMCC 7834T = JCM 30233T).
An extremely halophilic archaeon, strain IC35T, was isolated from a mud sample of the Aran-Bidgol salt lake in Iran. The novel strain was cream, non-motile, rod-shaped and required at least 2.5 M NaCl, but not MgCl2, for growth. Optimal growth was achieved with 3.4 M NaCl and 0.1 M MgCl2. The optimum pH and temperature for growth were pH 7.0 (grew over a pH range of 6.5–9.0) and 40 °C (grew over a temperature range of 30–50 °C), respectively. Analysis of 16S rRNA gene sequences revealed that strain IC35T clustered with species of the genus Halovivax , with sequence similarities of 97.3 %, 96.6 % and 96.3 %, respectively, to Halovivax limisalsi IC38T, Halovivax asiaticus EJ-46T and Halovivax ruber XH-70T. The rpoB′ gene similarities between the novel strain and Halovivax limisalsi IBRC-M 10022T, Halovivax ruber JCM 13892T and Halovivax asiaticus JCM 14624T were 90.2 %, 90.2 % and 89.9 %, respectively. The polar lipid pattern of strain IC35T consisted of phosphatidylglycerol and phosphatidylglycerol phosphate methyl ester; six unknown glycolipids and two minor phospholipids were also observed. The only quinone present was MK-8 (II-H2). The G+C content of the genomic DNA was 63.2 mol%. DNA–DNA hybridization studies (29 % hybridization with Halovivax limisalsi IBRC-M 10022T), as well as biochemical and physiological characterization, allowed strain IC35T to be differentiated from other species of the genus Halovivax . A novel species, Halovivax cerinus sp. nov., is therefore proposed to accommodate this strain. The type strain is IC35T ( = IBRC-M 10256T = KCTC 4050T).
An anaerobic, rod-shaped, hyperthermophilic and acidophilic crenarchaeon, designated strain CBA1501T, was isolated from solfataric soil of the Mayon volcano in the Republic of the Philippines. Phylogenetic analysis showed that strain CBA1501T is affiliated with the genus Vulcanisaeta in the phylum Crenarchaeota . DNA sequence similarities between the 16S rRNA gene of strain CBA1501T and those of Vulcanisaeta distributa IC-017T and Vulcanisaeta souniana IC-059T were 98.5 and 97.4 %, respectively. Strain CBA1501T grew between 75–90 °C, over a pH range of 4.0–6.0 and in the presence of 0–1.0 % (w/v) NaCl, with optimal growth occurring at 85 °C, pH 5.0, and with 0 % (w/v) NaCl. Fumarate, malate, oxidized glutathione, sulfur and thiosulfate were used as final electron acceptors, but FeCl3, nitrate and sulfate were not. The DNA G+C content of strain CBA1501T was 43.1 mol%. On the basis of polyphasic taxonomic analysis, strain CBA1501T represents a novel species of the genus Vulcanisaeta in the phylum Crenarchaeota , for which we propose the name Vulcanisaeta thermophila sp. nov. The type strain is CBA1501T ( = ATCC BAA-2415T = JCM 17228T).