Interdependence of respiratory NO reduction and nitrite reduction revealed by mutagenesis of nirQ, a novel gene in the denitrification gene cluster of Pseudomonas stutzeri

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Abstract
An open reading frame, designated nirQ, was identified upstream or nirS, the structural gene for the respiratory nitrite reductase or Pseudomonas stutzeri ZoBell. Its derived gene product (275 amino acids, M r = 30.544) shows similarity to the NtrC protein family or transcriptional activators. Deletion—replacement mutagenesis of the nirQ gene resulted in the simultaneous loss of nitrite reduction and NO reduction in vivo. However, both reductases were still synthesized, with only nitrite reductase being active in vitro. NO reductase was overproduced by a factor of about 2. Our results indicate that the systems for nitrite reduction and NO reduction are functionally coupled.