Identification and characterization of the Staphylococcus carnosus nitrate reductase operon

Physiological and genetic characterization of Staphylococcus carnosus nitrate reductase-negative mutants led to the identification of the nitrate reductase operon, narGHJI. Transcription from the nar promoter was stimulated by anaerobiosis, nitrate, and nitrite. This is in accordance with the nitrate reductase activities determined with benzyl viologen as electron donor. However, in the presence of oxygen and nitrate, high transcriptional initiation but low nitrate reductase activity was observed. Since the alphabeta complex of the nitrate reductase formed during anaerobic growth was insensitive to oxygen, other oxygen-sensitive steps (e.g., post-transcriptional mechanisms, molybdenum cofactor biosynthesis) must be involved. The nitrate-reducing system in S. carnosus displays similarities to the dissimilatory nitrate reductases of Escherichia coli. However, in the S. carnosus nar promoter, no obvious Fnr and integration host factor recognition sites are present; only one site that is related to the E. coli NarL consensus sequence was found. Studies to determine whether the E. coli proteins NarL and Fnr are functional at the S. carnosus narGHJI promoter indicated that the promoter is not functional in E. coli.