Identification and physiological characterization of the nitrogen fixing bacterium <em>Corynebacterium autotrophicum</em> <em>GZ 29</em>.

The coryneform hydrogen bacterium strain GZ 29, assigned to Corynebacterium autotrophicum fixed molecular nitrogen under autotrophic (H2, CO2) as well as under heterotrophic (sucrose) conditions. Physiological parameters of nitrogen fixation were measured under heterotrophic conditions. The optimal dissolved oxygen concentration for cells grown in a fermenter with N2 was rather low (0.14 mg O2/l) compared with cells grown in the presence of NH4 +(4.45 mg O2/l). C. autotrophicum GZ 29 had a doubling time of 3.7 h at 30°C with N2 as N-source and sucrose as carbon source and at optimal pO2. Acetylene reduction reached values of 12 nmoles of ethylene produced/minxmg protein. Although the oxygen concentration in the growing culture was kept constant, the optimal dissolved oxygen tension for the acetylene reduction assay shifted to higher pO2-values. The overall efficiency of nitrogen fixation amounted to 22 mg N fixed/g sucrose consumed; it reached a maximal value of 65 mg N fixed/g sucrose consumed at the beginning of the exponential growth phase. Intact cells reduced acetylene even under anaerobic test conditions; further anaerobic metabolic activity could not be ascertained so far