Galenea microaerophila gen. nov., sp. nov., a mesophilic, microaerophilic, chemosynthetic, thiosulfate-oxidizing bacterium isolated from a shallow-water hydrothermal vent

A mesophilic, strictly microaerophilic, chemosynthetic bacterium, designated strain P2D^T, was isolated from the sediment of an active shallow-water hydrothermal vent in Paleochori Bay, on the Greek island of Milos. The cells were Gram-staining-negative rods that measured approximately 0.8-1.3 μm in length and 0.4-0.5 μm in width. Strain P2D^T grew at 20-50 °C (optimum 35 °C), with 1.0-5.0 % (w/v) NaCl (optimum 3.0 %), and at pH 4.5-8.0 (optimum pH 5.5). The generation time under optimal conditions was 1.1 h. Growth occurred under chemolithoautotrophic conditions with S₂O₃^2- and CO₂ as the energy and carbon sources, respectively. Oxygen (5 %) was used as sole terminal electron acceptor. No growth was observed in the presence of acetate, formate, lactate, tryptone or peptone. Chemolithoheterotrophic growth occurred when d-glucose or sucrose were present as carbon sources. None of the organic compounds tested was used as an electron donor. The genomic DNA G+C content of the novel strain was 44.9 mol%. In a phylogenetic analysis based on 16S rRNA gene sequences, strain P2D^T was found to be most closely related to Thiomicrospira psychrophila DSM 13453^T (92.8% sequence similarity). Based on the phylogenetic, physiological and chemotaxonomic evidence, strain P2D^T represents a novel species of a new genus within the class Gammaproteobacteria of the family Piscirickettsiaceae, for which the name Galenea microaerophila gen. nov., sp. nov. is proposed. The type strain of the type species is P2D^T (= DSM 24963^T = JCM 17795^T).