Varunaivibrio sulfuroxidans gen. nov., sp nov., a facultatively chemolithoautotrophic, mesophilic alphaproteobacterium from a shallow-water gas vent at Tor Caldara, Tyrrhenian Sea

A mesophilic, facultatively anaerobic, facultatively chemolithoautotrophic bacterium, designated strain TC8(T), was isolated from a sulfidic shallow-water marine gas vent located at Tor Caldara, in the Tyrrhenian Sea, Italy. Cells were Gram-stain-negative curved rods with one or more polar flagella. Cells were approximately 1-1.5 mu m in length and 0.6 mu m in width. Strain TC8(T) grew between 20 and 35 degrees C (optimum 30 degrees C), with between 5 and 45 g NaCl l(-1) (optimum 15-20 g l(-1)) and between pH 4.5 and 8.5 (optimum pH 6.0-7.0). The generation time under optimal conditions was 8 h. Strain TC8(T) was a facultative chemolithoautotroph also capable of using organic substrates as electron donors and carbon sources. Chemolithoautotrophic growth occurred with sulfur and thiosulfate as the electron donors, CO2 as the carbon source, and nitrate, oxygen (5 %, v/v) and ferric iron as the electron acceptors. Chemoorganoheterotrophic growth occurred with tryptone, peptone, Casamino acids, pyruvate and glycerol as substrates, while chemolithoherotrophic growth occurred with D(+)-glucose, sucrose, yeast extract, acetate, lactate, citrate and L-glutamine. The G+C content of the genomic DNA was 59.9 mol%. Phylogenetic analysis of the 16S rRNA gene sequence of strain TC8(T) showed that this organism formed a lineage within the family Rhodospirillaceae, which branched separately from the two closest relatives, Magnetovibrio blakemorei MV1(T) (91.25% similarity) and Magnetospira thiophila MMS-1(T) (90.13 %). Based on phylogenetic, physiological and chemotaxonomic characteristics, it is proposed that the organism represents a novel species of a new genus within the family Rhodospirillaceae, Varunaivibrio sulfuroxidans gen. nov., sp. nov. The type strain of Varunaivibrio sulfuroxidans is TC8(T) (= DSM 101688(T) = JCM 31027(T)).