A novel thermophilic, anaerobic, hydrogen-oxidizing bacterium, designated strain AM1116T, was isolated from an East Pacific Rise hydrothermal vent sample. The cells were rod-shaped (1.01-5 x 0.5 microm), motile with polar flagella. They grew at temperatures between 50 and 70 degrees C (optimum 60 degrees C; doubling time approximately 1.5 h), at between pH 5.0 and 7.5 (optimum around pH 5.5-6.0) and in between 10 and 40 g NaCl l(-1) (optimum 20-25 g l(-1)). Cells grew chemolithoautotrophically in a H2/CO2 atmosphere (80:20; 200 kPa). Poor heterotrophic growth was observed on complex organic substrates. Elemental sulphur and nitrate served as electron acceptors, respectively yielding hydrogen sulphide and ammonia (doubling times were equal with the two electron acceptors). In contrast, when cystine was used as electron acceptor, growth was poor. The G+C content of the genomic DNA was 29 +/- 1 mol %. Phylogenetic analyses of the 16S rRNA gene located the strain within the epsilon-Proteobacteria, in the bacterial domain. On the basis of 16S rDNA sequence comparisons, physiological and biochemical characteristics, it is proposed that the isolate should be described as the type species of a new genus, Caminibacter gen. nov., as Caminibacter hydrogeniphilus sp. nov. The type strain is strain AM1116T (= DSM 14510T = CIP 107140T).