A Novel Bvg-Repressed Promoter Causes vrg -Like Transcription of fim3 but Does Not Result in the Production of Serotype 3 Fimbriae in Bvg - Mode Bordetella pertussis

• Published in: Journal of bacteriology 2018-10, Vol.200 (20)
• Main Authors: Chen, Qing, Lee, Gloria, Craig, Candice, Ng, Victoria, Carlson, Jr, Paul E, Hinton, Deborah M, Stibitz, Scott
• Format: Article
• Language: English
• Subjects: Bacteriology; Bordetella pertussis; Fim3 protein; Genes; Growth conditions; Modulators; Pertussis; Pili; Promoters; Proteins; Respiratory diseases; Transcription; Transcription factors; Translation; Virulence
• ISSN: 0021-9193; 1098-5530
• DOI: 10.1128/JB.00175-18

In , two serologically distinct fimbriae, FIM2 and FIM3, undergo on/off phase variation independently of each other via variation in the lengths of C stretches in the promoters for their major subunit genes, and These two promoters are also part of the BvgAS virulence regulon and therefore, if in an on configuration, are activated by phosporylated BvgA (BvgA~P) under normal growth conditions (Bvg mode) but not in the Bvg mode, inducible by growth in medium containing MgSO or other compounds, termed modulators. In the Tohama I strain (FIM2 FIM3 ), the promoter is in the off state. However, a high level of transcription of the gene is observed in the Bvg mode. In this study, we provide an explanation for this anomalous behavior by defining a Bvg-repressed promoter (BRP), located approximately 400 bp upstream of the P transcriptional start. Although transcription of the gene in the Bvg mode resulted in Fim3 translation, as measured by LacZ translational fusions, no accumulation of Fim3 protein was detectable. We propose that Fim3 protein resulting from translation of mRNA driven by BRP in the Bvg mode is unstable due to a lack of the fimbrial assembly apparatus encoded by the genes, located within the operon, and therefore is not expressed in the Bvg mode. In , the promoter P -15C for the major fimbrial subunit gene is activated by the two-component system BvgAS in the Bvg mode but not in the Bvg mode. However, many transcriptional profiling studies have shown that is transcribed in the Bvg mode even when P is in a nonpermissive state (P -13C), suggesting the presence of a reciprocally regulated element upstream of P Here, we provide evidence that BRP is the cause of this anomalous behavior of Although BRP effects -like transcription of in the Bvg mode, it does not lead to stable production of FIM3 fimbriae, because expression of the chaperone and usher proteins FimB and FimC occurs only in the Bvg mode.