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 ni trate reductase operon, narGHJI. Transcription from the nar promoter w as stimulated by anaerobiosis, nitrate, and nitrite. This is in accord ance with the nitrate reductase activities determined with benzyl viol ogen as electron donor. However, in the presence of oxygen and nitrate , high transcriptional initiation but low nitrate reductase activity w as observed. Since the ap complex of the nitrate reductase formed duri ng anaerobic growth was insensitive to oxygen, other oxygen-sensitive steps (e.g., posttranscriptional mechanisms, molybdenum cofactor biosy nthesis) must be involved. The nitrate-reducing system in S. carnosus displays similarities to the dissimilatory nitrate reductases of Esche richia coli. However, in the S. carnosus nar promoter, no obvious Fnr and integration host factor recognition sites are present; only one si te that is related to the E. coli NarL consensus sequence was found. S tudies to determine whether the E. coli proteins NarL and Fnr are func tional at the S. carnosus narGHJI promoter indicated that the promoter is not functional in E. coli.