Submerged culture of Magnetospirillum gryphiswaldense under N2-fixing condition and regulation of activity of nitrogen fixation

A submerged culture technique for Magnetospirillum gryphiswaldense under the nitrogen-fixing condition (microaerobic and N-limited) was set up. In N-limited medium with Na-lactate as a sole carbon source, the optical density (A _{600 nm}) and activity of nitrogen fixation of cells were 1.3 and 217 nmol of ethylene produced per hour per A _600nm respectively within 21 h by three times of feeds. The pH and temperature were controlled at 7.2 and 30°C respectively, and the oxygen concentration was controled by sparging with N₂ containing 0.4%–0.8% of O₂. The activity of nitrogen fixation of cells was obviously inhibited by oxygen and ammonium. It indicated that the posttranslational regulation of nitrogenase existed in M. gryphiswaldense.