Nitrogen-fixing Ability of a Thermophilic Sulfate-reducing Bacterium in the Genus Thermodesulfovibrio Isolated from a Terrestrial Hot Spring in Japan

Nitrogen-fixing sulfate-reducing bacteria have not yet been exami-ned in thermal environments. In this study, strain TK110, belonging to the genus Thermodesulfovibrio, was successfully isolated from a geothermal spring using an NH3-free inorganic medium. Strain TK110 harbored genes associated with the Calvin-Benson-Bassham cycle and nitrogen fixation-related genes, nifHDKENXIIB. Nitrogenase activity was assessed using an acetylene reduction assay and detected in strain TK110 under autotrophic conditions, as well as in Thermodesulfovibrio yellowstonii DSM 11347T under heterotrophic conditions at 65°C. To the best of our knowledge, this is the first study to demonstrate nitrogen fixation by thermophilic sulfate-reducing bacteria.