Virulence gene regulation in Bordetella

Mason, Eliza

Virulence gene regulation in Bordetella Public Deposited

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March 22, 2019

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Mason, Eliza
- Affiliation: School of Medicine, Department of Microbiology and Immunology

Abstract

Bordetella species cause respiratory infections in mammals. Their master regulatory system BvgAS controls expression of at least three distinct phenotypic phases in response to environmental cues. The Bvg+ phase is necessary and sufficient for respiratory infection while the Bvg- phase is required for survival ex vivo. We developed a plasmid, pGFLIP, that encodes a sensitive Flp recombinase-based fluorescent reporter system able to document gene activation both in vitro and in vivo. Using pGFLIP, we demonstrated that cyaA, considered to be a late Bvg+ phase gene, is activated substantially earlier in B. bronchiseptica compared to B. pertussis following a switch from Bvg- to Bvg+ phase conditions. We show that the altered activation of cyaA is not due to differences in the cyaA promoter or in the bvgAS alleles of B. bronchiseptica compared to B. pertussis, but appears to be species-specific. Finally, we used pGFLIP to show that flaA remains repressed during infection, confirming that wild-type B. bronchiseptica do not modulate to the Bvg- phase in vivo. Additionally, we obtained large colony variants (LCVs) from the lungs of mice infected with B. bronchiseptica strain RBX9, which contains an in-frame deletion mutation in fhaB, encoding filamentous hemagglutinin. RBX9 also yielded LCVs when switched from Bvg- phase conditions to Bvg+ phase conditions in vitro. We determined that LCVs are composed of both Bvg+ and Bvg- phase bacteria and that they result from defective bvgAS positive autoregulation. The LCV phenotype was linked to the presence of a divergent promoter 5' to bvgAS, suggesting a previously undescribed mechanism of transcriptional interference that, in this case, leads to feedback-based multistability (FBM). Our results also indicate that a small proportion of RBX9 bacteria modulates to the Bvg- phase in vivo. In addition to providing insight into transcriptional interference and FBM, our data provide an example of an in-frame deletion mutation exerting a `polar' effect on nearby genes

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