A novel thermophilic, microaerophilic, facultatively chemolithoheterotrophic bacterium designated strain TR(T) was isolated from a sample of a deep-sea hydrothermal chimney collected at the Rainbow vent field on the Mid-Atlantic Ridge (36 degrees 14'N). Gram-negative, non-spore-forming, non-motile rods occurred singly or in pairs. The organism grew in the temperature range 37-80 degrees C with an optimum at 70 degrees C and at pH 5.5-8.4 with an optimum around 6.7. The NaCl range for growth was 10-50 g l(-1) with an optimum of 30 g l(-1). Strain TR(T) grew chemoorganoheterotrophically with carbohydrates, proteinaceous substrates, organic acids and alcohols using oxygen or nitrate as electron acceptors. The isolate was able to grow at oxygen concentrations from 0.5 to 21%. Oxygen concentrations that promoted fastest growth ranged from 4 to 8% under agitation. The novel isolate was able to grow lithoheterotrophically with molecular hydrogen as the energy source. The G + C content of the genomic DNA was 68.4 mol%. Phylogenetic analysis of the 16S rDNA sequence placed strain TR(T) within the phylum Deinococcus-Thermus of the Bacteria. On the basis of phenotypic and phylogenetic data, it is proposed that this isolate should be described as a member of a novel species of a new genus as Vulcanithermus mediatlanticus gen. nov., sp. nov. The type strain is TR(T) (= DSM 14978T = VKM B-2292T = JCM 11956T).