The Chromosomal Location and Pleiotropic Effects of Mutations of the nirA+ Gene of Escherichia coli k12: The Essential Role of nirA+ in Nitrite Reduction and in Other Anaerobic Redox Reactions

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Abstract
Cytochrome c552, which was implicated as an electron carrier for nitrite reduction by E. coli, was separated from NADH-nitrite oxidoreductase activity. The cytochrome is therefore not required for the reduction of nitrite by NADH in vitro. Nevertheless, some mutants which were selected by their inability to use nitrite as a N source during anaerobic growth synthesize neither NADH-nitrite oxidoreductase nor cytochrome c552. The defects in these mutants are due to mutations in a single gene, nirA, which is located at about 29 min on the recalibrated linkage map. Experiments with an F'' plasmid which carries a nirA+ allele established that nirA+ is dominant to the defective allele. Other mutants, defective in nitrate reductase activity because of mutations in the chlA or chlB genes, synthesized nitrite reductase and cytochrome c552 in the absence of nitrate or nitrite. A mutant with a defective fnr gene was also NirA- and conversely, nirA mutants were Fnr-. In a series of transduction experiments, attempts to separate the nirA and fnr defects were unsuccessful. Furthermore, no complementation was observed when an F'' plasmid carrying a defective nirA allele was transferred into the fnr strain. The fnr gene is identical to the nirA gene and its product affects the synthesis or assembly of a variety of anaerobic redox enzymes which include nitrite reductase, cytochrome c552, nitrate reductase, fumarate reductase and formate hydrogenlyase.