Expression of Klebsiella pneumoniae Nitrogen Fixation Genes in Nitrate Reductase Mutants of Escherichia coli

Nitrate reductase (nar) A, B and E mutants of Escherichia coli with plasmids carrying Klebsiella pneumoniae nitrogen fixation (nif) genes reduced acetylene independently of added molybdate, but narD mutants showed pleiotropic de-pendence on the concentration of added molybdate for expression of both nar and nif: No complementation of nar mutations by nifoccurred; nitrite but not nitrate repressed nif in nar hosts. Derepression of nif occurred in molybdenum-deficient narD (nif) strains since nitrogenase peptides were present. nifB mutants, thought to have a lesion in the pathway of molybdenum to nitrogenase, as well as nif deletion mutants, had normal nitrate reductase activity