Salinisphaera hydrothermalis sp. nov., a mesophilic, halotolerant, facultatively autotrophic, thiosulfate-oxidizing gammaproteobacterium from deep-sea hydrothermal vents, and emended description of the genus Salinisphaera

A mesophilic, aerobic, facultatively chemolithoautotrophic bacterium, designated strain EPR70^T, was isolated from hydrothermal fluids from diffuse-flow vents on the East Pacific Rise at 9° 50′ N 104° 17′ W. Cells were Gram-negative rods, approximately 0.8-1.0 μm long and 0.3-0.5 μm wide. Strain EPR70^T grew at 20-40 °C (optimum 30-35 °C), 1-25% NaCl (optimum 2.5 %) and pH 5.0-7.5 (optimum pH 5.5). The shortest generation time observed for strain EPR70^T was 42 min. Growth occurred under aerobic chemolithoautotrophic conditions in the presence of thiosulfate and CO₂. Strain EPR70^T grew heterotrophically with acetate or n-alkanes as sole carbon and energy sources, and in complex artificial seawater medium. Nitrate was not used as an electron acceptor. The G+C content of the genomic DNA was 64 mol%. Phylogenetic analysis of the 16S rRNA gene indicated that this organism is a member of the class Gammaproteobacteria, with Salinisphaera shabanensis E1L3A^T as its closest relative (94% sequence similarity). On the basis of phylogenetic analyses based on 16S rRNA, rbcL and alkB genes and physiological analysis, it is proposed that the organism represents a novel species within the genus Salinisphaera, for which the name Salinisphaera hydrothermalis sp. nov. is proposed. The type strain is EPR70^T (=DSM 21483^T =JCM 15514^T).