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

Abstract

Nitrogen-fixing sulfate-reducing bacteria have not yet been exami­ned 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 11347^T 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.