The Bordetella pertussis model of exquisite gene control by the global transcription factor BvgA.
ABSTRACT Bordetella pertussis causes whooping cough, an infectious disease that is reemerging despite widespread vaccination. A more complete understanding of B. pertussis pathogenic mechanisms will involve unravelling the regulation of its impressive arsenal of virulence factors. Here we review the action of the B. pertussis response regulator BvgA in the context of what is known about bacterial RNA polymerase and various modes of transcription activation. At most virulence gene promoters, multiple dimers of phosphorylated BvgA (BvgA~P) bind upstream of the core promoter sequence, using a combination of high- and low-affinity sites that fill through cooperativity. Activation by BvgA~P is typically mediated by a novel form of class I/II mechanisms, but two virulence genes, fim2 and fim3, which encode serologically distinct fimbrial subunits, are regulated using a previously unrecognized RNA polymerase/activator architecture. In addition, the fim genes undergo phase variation because of an extended cytosine (C) tract within the promoter sequences that is subject to slipped-strand mispairing during replication. These sophisticated systems of regulation demonstrate one aspect whereby B. pertussis, which is highly clonal and lacks the extensive genetic diversity observed in many other bacterial pathogens, has been highly successful as an obligate human pathogen.
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ABSTRACT: Pertussis is a highly infectious respiratory disease of humans caused by the bacterium Bordetella pertussis. Despite high vaccination coverage, pertussis has re-emerged globally. Causes for the re-emergence of pertussis include limited duration of protection conferred by acellular pertussis vaccines (aP) and pathogen adaptation. Pathogen adaptations involve antigenic divergence with vaccine strains, the emergence of strains which show enhanced in vitro expression of a number of virulence-associated genes and of strains that do not express pertactin, an important aP component. Clearly, the identification of more effective B. pertussis vaccine antigens is of utmost importance. To identify novel antigens, we used proteomics to identify B. pertussis proteins regulated by the master virulence regulatory system BvgAS in vitro. Five candidates proteins were selected and it was confirmed that they were also expressed in the lungs of naïve mice seven days after infection. The five proteins were expressed in recombinant form, adjuvanted with alum and used to immunize mice as stand-alone antigens. Subsequent respiratory challenge showed that immunization with the autotransporters Vag8 and SphB1 significantly reduced bacterial load in the lungs. Whilst these antigens induced strong opsonizing antibody responses, we found that none of the tested alum-adjuvanted vaccines - including a three-component aP - reduced bacterial load in the nasopharynx, suggesting that alternative immunological responses may be required for efficient bacterial clearance from the nasopharynx.PLoS ONE 08/2014; 9(8):e105011. DOI:10.1371/journal.pone.0105011 · 3.53 Impact Factor
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ABSTRACT: Two-component systems [sensor kinase/response regulator (RR)] are major tools used by microorganisms to adapt to environmental conditions. RR phosphorylation is typically required for gene activation, but few studies have addressed how and if phosphorylation affects specific steps during transcription initiation. We characterized transcription complexes made with RNA polymerase and the Bordetella pertussis RR, BvgA, in its nonphosphorylated or phosphorylated (BvgA∼P) state at Pfim3, the promoter for the virulence gene fim3 (fimbrial subunit), using gel retardation, potassium permanganate and DNase I footprinting, cleavage reactions with protein conjugated with iron bromoacetamidobenzyl-EDTA, and in vitro transcription. Previous work has shown that the level of nonphosphorylated BvgA remains high in vivo under conditions in which BvgA is phosphorylated. Our results here indicate that surprisingly both BvgA and BvgA∼P form open and initiating complexes with RNA polymerase at Pfim3. However, phosphorylation of BvgA is needed to generate the correct conformation that can transition to competent elongation. Footprints obtained with the complexes made with nonphosphorylated BvgA are atypical; while the initiating complex with BvgA synthesizes short RNA, it does not generate full-length transcripts. Extended incubation of the BvgA/RNA polymerase initiated complex in the presence of heparin generates a stable, but defective species that depends on the initial transcribed sequence of fim3. We suggest that the presence of nonphosphorylated BvgA down-regulates Pfim3 activity when phosphorylated BvgA is present and may allow the bacterium to quickly adapt to the loss of inducing conditions by rapidly eliminating Pfim3 activation once the signal for BvgA phosphorylation is removed.Proceedings of the National Academy of Sciences 01/2015; DOI:10.1073/pnas.1421045112 · 9.81 Impact Factor
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ABSTRACT: The fimbriae of Bordetella pertussis are required for colonisation of the human respiratory tract. Two serologically distinct fimbrial subunits, Fim2 and Fim3, having been considered important vaccine components for many years, are included in the Sanofi Pasteur 5-component acellular pertussis vaccine, and the World Health Organisation recommends the inclusion of strains expressing both fimbrial serotypes in whole cell pertussis vaccines. Each of the fimbrial major subunit genes, fim2, fim3, and also fimX, has a promoter poly(C) tract upstream of its -10 box. Such monotonic DNA elements are susceptible to changes in length via slipped-strand mispairing in vitro and in vivo, which can potentially cause on/off switching of genes at every cell division. Here we describe intra-culture variability in poly(C) tract lengths and in the resulting fimbrial phenotypes in 22 recent United Kingdom B. pertussis isolates. Owing to the highly plastic nature of the fimbrial promoters, we used the same cultures for both genome sequencing and flow cytometry. Individual cultures of B. pertussis each contained multiple fimbrial serotypes and multiple different fimbrial promoter poly(C) tract lengths, which supports earlier serological evidence that B. pertussis expresses both serotypes during infection.Microbiology 07/2014; 160. DOI:10.1099/mic.0.079251-0 · 2.84 Impact Factor