Oxygen requirement for acetylene reduction by pure cultures of rhizobia

The oxygen and nutritional requirements for acetylene reduction by Rhizobium japonicum and Rhizobium sp. in liquid culture are described. The optimal oxygen concentration was about 0.1% in the gas phase, which is lower than that of any other known aerobic nitrogen-fixing microorganism. these organisms are also unique in that nitrogenase synthesis is not repressed in the presence of ammonium chloride under certain cultural conditions, in contrast to other wild-type bacteria.