title: Regulation of nitrogen fixation in Klebsiella pneumoniae: evidence for a role of glutamine synthetase as a regulator of nitrogenase synthesis.
abstract: Mutations causing constitutive synthesis of glutamine synthetase (GlnC(-) phenotype) were transferred from Klebsiella aerogenes into Klebsiella pneumoniae by P1-mediated transduction. Such GlnC(-) strains of K. pneumoniae have constitutive levels of glutamine synthetase. Two of three GlnC(-) strains of K. pneumoniae studied, each containing independently isolated mutations that confer the GlnC(-) phenotype, continue to synthesize nitrogenase in the presence of NH(4) (+). One strain, KP5069, produces 30% as much nitrogenase when grown in the presence of 15 mM NH(4) (+) as in its absence. The GlnC(-) phenotype allows the synthesis of nitrogenase to continue under conditions that completely repress nitrogenase synthesis in the wild-type strain. Glutamine auxotrophs of K. pneumoniae, that do not produce catalytically active glutamine synthetase, are unable to synthesize nitrogenase during nitrogen limited growth. Complementation of K. pneumoniae Gln(-) strains by an Escherichia coli episome (F'133) simultaneously restores glutamine synthetase activity and the ability to synthesize nitrogenase. These results indicate a role for glutamine synthetase as a positive control element for nitrogen fixation in K. pneumoniae.
mesh_terms: D002384:Catalysis; D003470:Culture Media; D005816:Genetic Complementation Test; D005838:Genotype; D005974:Glutamate-Ammonia Ligase / Q000502:physiology*; D005973:Glutamine / Q000378:metabolism; D007709:Klebsiella / Q000378:metabolism; D007711:Klebsiella pneumoniae / Q000201:enzymology*; D009154:Mutation; D009586:Nitrogen Fixation; D009591:Nitrogenase / Q000096:biosynthesis*; D009876:Operon; D010641:Phenotype; D014161:Transduction, Genetic
chemical_list: D003470:Culture Media; D005973:Glutamine; D009591:Nitrogenase; D005974:Glutamate-Ammonia Ligase