Nitrogenase Activity in Thermophilic Chemolithoautotrophic Bacteria in the Phylum Aquificae Isolated under Nitrogen-Fixing Conditions from Nakabusa Hot Springs.

摘要: The phylum Aquificae comprises chemolithoautotrophic thermophilic to hyperthermophilic bacteria, in which the nitrogenase reductase gene (nifH) has been reported. However, nitrogen-fixing activity not yet demonstrated members of this deeply branching bacterial phylum. We isolated two diazotrophic strains from chemosynthetic microbial communities slightly alkaline hot springs (≥70°C) Nakabusa, Nagano Prefecture, Japan. A phylogenetic analysis based on 16S rRNA genes identified these as genus Hydrogenobacter within Aquificae. Their NifH sequences showed 96.5 and 97.4% amino acid sequence identities that thermophilus TK-6. Nitrogenase activity, measured by acetylene reduction, was confirmed both at 70°C. These novel grew under semi-aerobic conditions using CO2 sole carbon source N2 nitrogen media containing hydrogen and/or thiosulfate. To best our knowledge, is first demonstration active fixation bacteria 70°C