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Nitrogenase repression in Klebsiella pneumoniae
Nitrogenase biosynthesis in a mutant strain of Klebsiella.pneumoniae can be fully repressed by L-glutamine alone. K.pneumoniae SK-25 which has no glutamine synthetase activity or immunologically cross reacting protein, lacks glutamate synthase activity, and has repressed levels of glutamate dehydrogenase cannot directly utilize NH4+, and thus requires L-glutamine as a fixed nitrogen source for growth. When grown in sulfate ion limited chemostat cultures under argon, the presence of excess L-glutamine will fully repress nitrogenase activity. In L-glutamine limited chemostat cultures and in batch cultures, nitrogenase was partly derepressed. These findings indicate that the presence of L-glutamine as a fixed nitrogen source can affect the regulation of nitrogenase by a mechanism which is independent of the adenylylation of glutamine synthetase.