The multifaceted RisA regulon of Bordetella pertussis

Abstract

The whooping cough agent Bordetella pertussis regulates the production of its virulence factors by the BvgA/S system. Phosphorylated BvgA activates the virulence-activated genes (vags) and represses the expression of the virulence-repressed genes (vrgs) via the activation of the bvgR gene. In modulating conditions, with MgSO4, the BvgA/S system is inactive, and the vrgs are expressed. Here, we show that the expression of almost all vrgs depends on RisA, another transcriptional regulator. We also show that some vags are surprisingly no longer modulated by MgSO4 in the risA− background. RisA also regulates the expression of other genes, including chemotaxis and flagellar operons, iron-regulated genes, and genes of unknown function, which may or may not be controlled by BvgA/S. We identified RisK as the likely cognate RisA kinase and found that it is important for expression of most, but not all RisA-regulated genes. This was confirmed using the phosphoablative RisAD60N and the phosphomimetic RisAD60E analogues. Thus the RisA regulon adds a new layer of complexity to B. pertussis virulence gene regulation.

The BvgAS Regulon of Bordetella pertussis

“…Our analyses confirm and extend results from previous microarray analyses (9,31,32). As expected, we observed the activation of multiple well-known vags, such as genes encoding adhesins and toxins (Table S2), T3SS (Table S2), and transcriptional regulators (Table 1).…”

“…Microarray analyses identified~250 genes regulated in B. pertussis Tohama I BP536 and nearly 500 genes regulated in B. bronchiseptica RB50 (9,31). Known vags, including those encoding adhesins and toxins, were expressed consistently in both species in the Bvg(ϩ) mode, while more species-specific differences were observed in the Bvg(Ϫ) mode.…”

“…Two hundred forty-five genes were identified as positively regulated by BvgA~P (Table S1B). Category 1 (Tables 2 and S2) contains well-known vags, such as virulence determinants and accessory factors, that have been identified by previous genetic and microarray studies (9,10,31,(33)(34)(35)(36); these include filamentous hemagglutinin/adhesin (fhaB and fhaC), adenylate cyclase toxins (cyaABCDE), fimbriae (fimABCD), pertactin (prn), pertussis toxins (ptxABDEC), and type 4 secretion system proteins (ptlABCDIEFGH). RT-qPCR confirmed the significant increase in RNA levels of several of these vags (Fig.…”

Activation of Bvg-Repressed Genes in Bordetella pertussis by RisA Requires Cross Talk from Noncooperonic Histidine Kinase RisK

“…This observation suggests the presence of significant metabolic alterations in the deletion strain that could result in profound regulatory effects that are not necessarily representative of natural regulatory circuits. Interestingly, transcriptomic analyses of these strains did in fact reveal the presence of a class of genes that are expressed at much lower levels in the ΔrisA strain but not in the risA D60N strain, consistent with this explanation (32). Further work will be necessary to elucidate the true nature of these effects of RisA on transcription of Pfha and other Bvg-activated genes.…”

Stand-Alone EAL Domain Proteins Form a Distinct Subclass of EAL Proteins Involved in Regulation of Cell Motility and Biofilm Formation in Enterobacteria

“…Thus, we hypothesize that motility is not the only physiological output of these proteins. The nonmotile whooping cough agent Bordetella pertussis still carries certain chemotaxis and flagellar genes, including flhD, which are negatively regulated by the EAL-only protein BvgR (20,57). Although BvgR has a sequence quite distinct from that of STM1344/STM1697 (Fig.…”