Involvement of the Arc system in redox regulation of the Cob operon in Salmonella typhimurium.

Transcription of the cobalamin biosynthetic (cob) genes in Salmonella typhimurium is induced during anaerobic growth. Two mutants defective in induction of the Cob operon were isolated. The mutants showed decreased anaerobic induction, both during conditions of fermentation and anaerobic respiration, relative to the wild type. The mutant genes were localized by Hfr and transduction mapping to 100 minutes and 69 minutes on the chromosome. The mutants were sensitive to the dye toluidine blue. The mapping and the dye sensitivity suggest that these mutants are defective in the arcA and arcB genes, not previously identified in Salmonella typhimurium. Thus the regulatory function of the Arc system is expanded to include anaerobic activation of the Cob operon.