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Regulation of nitrogenase biosynthesis in Klebsiella pneumoniae: effect of nitrate.

The rate of biosynthesis of nitrogenase polypeptides in Klebsiella pneumoniae was determined in a medium containing NaNO3 or NaNO2. Nitrogenase biosynthesis was completely repressed by NO3- in a mutant strain, strain SK-25, that is derepressed for nitrogenase biosynthesis in the presence of NH4+. Chlorate-resistant mutants, derived from strain SK-25, that are defective in NO3- respiration produced nitrogenase in the presence of NO3-. Strain SK-56), a chlorate-resistant derivative capable of NO3- respiration, produced no nitrogenase in the presence of NO3- or NO2-. Klebsiella pneumoniae respired under anaerobic conditions utilizing either NO3- or NO2- as terminal electron acceptor. A mechanism for the control of nitrogenase biosynthesis is discussed involving the redox control of anaerobic enzyme systems.