The utilization of nitrogen in various compounds by Clostridium pasteurianum.

In biological nitrogen fixation the key intermediate compound, defined as the end product of the fixation reaction and the initial reactant of assimilation, is believed to be either ammonia or hydroxylamine. Burris and Wilson (1945) noted that these two possibilities need not be mutually exclusive but may occur simultaneously, depending on the concentrations of the carbon compounds serving as acceptors, e.g., keto acids. It is also possible that hydroxylamine may precede ammonia in the reaction chain of fixation and still not be a key intermediate in the sense that ammonia alone is concerned in the assimilation reaction. Hydroxylamine does not appear to be a likely intermediate in nitrogen fixation by Azotobacter vinelandii, strain 0, since neither nontoxic concentrations of salts of this base nor oximes of the common keto acids are used by growing cells (Novak and Wilson, 1948; Segal and Wilson, 1949). To provide information dealing with the comparative physiology of biological nitrogen fixation, we have recently completed similar investigations with the anaerobic nitrogen fixer, Clostridium pasteurianum, strain W5.