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A new mesophilic bacterium, designated strain 13-15A T , was isolated from the deep-sea water from the Carlsberg Ridge, northwestern Indian Ocean. Cells were short rods and motile with a single polar flagellum. Growth was observed in the presence of 85-1700 mM NaCl (optimum 680 mM), at 10-45 °C (optimum, 28 °C) and pH 5.0-9.0 (optimum, pH 7.0). The isolate was an obligate chemolithoautotroph capable of growth using thiosulfate, sulfide, elemental sulfur or tetrathionate as the sole energy source, carbon dioxide as the sole carbon source, and molecular oxygen as the sole electron acceptor. Molecular hydrogen did not support growth. The major fatty acids were C 16 : 1 (45.0 %), C 18 : 1 (22.5 %) and C 16 : 0 (20.1 %). The G+C content of the genomic DNA was 41.6 mol%. The results of phylogenetic analysis based on 16S rRNA gene sequences showed that the novel isolate belonged to the genus Thiomicrorhabdus and was most closely related to Thiomicrorhabdus hydrogeniphila MAS2 T (94.8 % sequence similarity). On the basis of the taxonomic data obtained in this study, strain 13-15A T represents a novel species of the genus Thiomicrorhabdus , for which the name Thiomicrorhabdus indica sp. nov. is proposed, with the type strain 13-15A T (=MCCC 1A13986 T =KCTC 15750 T ).

Thiomicrospira species are ubiquitously found in various marine environments and appear particularly common in hydrothermal vent systems. Members of this lineage are commonly classified as sulfur-oxidizing chemolithoautotrophs. Although sequencing of Thiomicrospira crunogena's genome has revealed genes that encode enzymes for hydrogen uptake activity and for hydrogenase maturation and assembly, hydrogen uptake ability has so far not been reported for any Thiomicrospira species. We isolated a Thiomicrospira species (SP-41) from a deep sea hydrothermal vent and demonstrated that it can oxidize hydrogen. We show in vivo hydrogen consumption, hydrogen uptake activity in partially purified protein extracts and transcript abundance of hydrogenases during different growth stages. The ability of this strain to oxidize hydrogen opens up new perspectives with respect to the physiology of Thiomicrospira species that have been detected in hydrothermal vents and that have so far been exclusively associated with sulfur oxidation.

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 S₂O₃²⁻ and CO(2) 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)).