Autogenous regulation of the Bordetella pertussis bvgABC operon

The bvgABC operon of the bacterial pathogen Bordetella pertussis encodes a sensory transduction system that regulates the expression of several virulence genes in response to environmental stimuli. In this study we have examined the transcriptional regulation of the bvgABC operon. Transcriptional bvg::lacZYA fusions in Escherichia coli show that the bvgABC operon is autogenously activated. Autoactivation is inhibited by the same environmental stimuli that result in the lack of expression of bvg-activated genes in B. pertussis. These observations were confirmed in B. pertussis using a chromosomal chloramphenicol acetyltransferase transcriptional fusion in bvgC. Transcriptional initiation sites upstream of bvgA were mapped by primer extension analysis in E. coli and B. pertussis. Two differentially regulated bvg promoters were identified. The bvgP1 promoter is a positively autoregulated promoter located 90 base pairs upstream of bvgA. The bvgP2 promoter is located 141 base pairs upstream of bvgA and does not appear to require any positive regulatory factors for activity. These results suggest a model describing the regulatory events that take place upstream of the bvgABC operon.