Phenotypic changes in hydrogen evolving chemostat cultures of Rhodopseudomonas capsulata

Spontaneous nitrogenase‐negative (Nif− mutants of Rhodopseudomonas capsulata were observed to accumulate with time in ammonium‐ or glutamate‐limited chemostat cultures. Nif− mutants were characterized by their inability to grow under N2 and to reduce acetylene or produce hydrogen gas when grown on glutamate. They lacked the nitrogenase structural proteins as evidenced by immunological techniques. On the other hand, no significant differences were found in the pathways of ammonia assimilation between the Nif− mutants and the wild‐type strain. The Nif− mutants seem to result from a mutation in a regulatory gene.