A new isolate of Hydrogenobacter, an obligately chemolithoautotrophic, thermophilic, halophilic and aerobic hydrogen-oxidizing bacterium from seaside saline hot spring

An obligately chemolithoautotrophic and aerobic hydrogen-oxidizing bacterium was isolated from a seaside saline hot spring in Izu Peninsula, Japan. The isolate was a Gram-negative, non-motile, non-spore-forming rod cell measuring 0.3 to 0.5 by 1.0 to 2.5 µm. The optimal temperature for growth was around 70°C, and no growth was observed at 40°C or 80°C. Elemental sulfur or thiosulfate could be an alternative to molecular hydrogen as the sole energy source. The DNA base composition of the isolate was 46.0 mol% G+C. 2-Methylthio-3-VI,VII-tetrahydromultiprenyl⁷-1,4-naphthoquinone (methionaquinone) was the major component of the quinone system. C_18:0, C_18:1 and C_20:1 were the major components of the cellular fatty acids. These properties clearly indicate that the isolate belongs to genus Hydrogenobacter, but differed from H. thermophilus in some respects. Specifically, the isolate was a halophile which grew optimally at around 0.3–0.5 M NaCl, while H. thermophilus could not grow at such NaCl concentration levels. A new species name H. halophilus is proposed for this new halophilic isolate.