Strains PRI 2268 and PRI 3838T were isolated from two separate hot springs in the Torfajokull geothermal area of South Iceland. The cells were non-motile rods, approximately 0.3 μm in width and 1.5–2.5 μm in length. Electron microscopy revealed a Gram-negative cell-wall structure. The strains grew at 45–79 °C (optimum, 65 °C) and pH 5.5–10.5 (optimum, pH 6.0–7.0). 16S rRNA gene sequence analysis indicated that they formed a separate branch within the genus Thermus with ‘Thermus kawarayensis’ KW11 as their closest cultured relative (96.5 % similarity). The gene sequence similarities of both new isolates to Thermus aquaticus YT-1T and Thermus igniterrae RF-4T were 96.1 % and 95.5 %, respectively. DNA–DNA relatedness between strain PRI 3838T and ‘T. kawarayensis’ was 46.1 %. The DNA G+C content of strain PRI 3838T was 69.0 mol%. The predominant menaquinones, pigmentation, fatty acid profiles and phospholipid profiles of the novel strains were similar to those of other members of the genus Thermus. However, the new strains could be differentiated from the type strains of all other species of the genus Thermus by their lack of catalase activity and their utilization of only a few carbon sources. Furthermore, the novel strains exhibited mixotrophic growth with sulfur oxidation. On the basis of 16S rRNA gene sequence comparisons, DNA–DNA hybridization and physiological and biochemical characteristics, the new isolates represent a novel species. Since the species appears to be ubiquitous in Icelandic hot springs, the name Thermus islandicus sp. nov. is proposed. The type strain is PRI 3838T (=DSM 21543T=ATCC BAA-1677T).
A novel thermophilic, heterotrophic bacterium, strain TBF 19.5.1T, was isolated from oil production fluid at the Troll B oil platform in the North Sea. Cells of strain TBF 19.5.1T were non-motile rods with a sheath-like structure, or toga. The strain was Gram-negative and grew at 20–80 °C (optimum 65 °C), pH 5.5–8.0 (optimum pH 6.8) and NaCl concentrations of 10–60 g l−1 (optimum 25–30 g l−1). For a member of the order Thermotogales, the novel isolate is capable of unprecedented growth at low temperatures, with an optimal doubling time of 175 min (specific growth rate 0.24 h−1) and a final optical density of >1.4 when grown on pyruvate at 37 °C. Various carbohydrates, proteinaceous compounds and pyruvate served as growth substrates. Thiosulfate, but not elemental sulfur, enhanced growth of the isolate. Sulfate also enhanced growth, but sulfide was not produced. The strain grew in the presence of up to approximately 15 % oxygen, but only if cysteine was included in the medium. Growth of the isolate was inhibited by acetate, lactate and propionate, while butanol and malate prevented growth. The major fermentation products formed on maltose were hydrogen, carbon dioxide and acetic acid, with traces of ethanol and propionic acid. The G+C content of the genomic DNA was 42.5 mol%. Phylogenetic analyses of the 16S and 23S rRNA gene sequences as well as 29 protein-coding ORFs placed the strain within the bacterial order Thermotogales. Based on the phylogenetic analyses and the possession of a variety of physiological characteristics not previously found in any species of this order, it is proposed that the strain represents a novel species of a new genus within the family Thermotogaceae, order Thermotogales. The name Kosmotoga olearia gen. nov., sp. nov. is proposed. The type strain of Kosmotoga olearia is TBF 19.5.1T (=DSM 21960T =ATCC BAA-1733T).