The Bvg accessory factor (Baf) enhances pertussis toxin expression in Escherichia coli and is essential for Bordetella pertussis viability

Pertussis toxin expression in the Gram-negative respiratory pathogen, Bordetella pertussis, is regulated by the BvgAS two-component system. Previous studies suggested that an additional gene encoding a Bvg accessory factor (Baf) was required, along with BvgAS, for expression of a ptx-lacZ fusion in Escherichia coli grown in rich medium. However, other studies showed that BvgAS is sufficient for ptx-lacZ expression in minimal medium. Here we show that Baf acts with BvgAS to further increase ptx-lacZ expression in E. coli grown in minimal media and this is concomitant with a two-fold increase in BvgA protein levels. Gene replacement experiments show that baf is essential for viability of B. pertussis, suggesting that Baf affects the expression of other genes in addition to ptx.     

The Bvg virulence control system regulates biofilm formation in Bordetella bronchiseptica

Bordetella species utilize the BvgAS (Bordetella virulence gene) two-component signal transduction system to sense the environment and regulate gene expression among at least three phases: a virulent Bvg+ phase, a nonvirulent Bvg- phase, and an intermediate Bvgi phase. Genes expressed in the Bvg+ phase encode known virulence factors, including adhesins such as filamentous hemagglutinin (FHA) and fimbriae, as well as toxins such as the bifunctional adenylate cyclase/hemolysin (ACY). Previous studies showed that in the Bvgi phase, FHA and fimbriae continue to be expressed, but ACY expression is significantly downregulated. In this report, we determine that Bordetella bronchiseptica can form biofilms in vitro and that the generation of biofilm is maximal in the Bvgi phase. We show that FHA is required for maximal biofilm formation and that fimbriae may also contribute to this phenotype. However, expression of ACY inhibits biofilm formation, most likely via interactions with FHA. Therefore, the coordinated regulation of adhesins and ACY expression leads to maximal biofilm formation in the Bvgi phase in B. bronchiseptica.     

Expression of small RNAs of Bordetella pertussis colonizing murine tracheas

We performed RNA sequencing on Bordetella pertussis, the causative agent of whooping cough, and identified nine novel small RNAs (sRNAs) that were transcribed during the bacterial colonization of murine tracheas. Among them, four sRNAs were more strongly expressed in vivo than in vitro. Moreover, the expression of eight sRNAs was not regulated by the BvgAS two-component system, which is the master regulator for the expression of genes contributing to the bacterial infection. The present results suggest a BvgAS-independent gene regulatory system involving the sRNAs that is active during B. pertussis infection.     

The BvgAS signal transduction system regulates biofilm development in Bordetella

The majority of Bordetella sp. virulence determinants are regulated by the BvgAS signal transduction system. BvgAS mediates the control of multiple phenotypic phases and a spectrum of gene expression profiles specific to each phase in response to incremental changes in the concentrations of environmental signals. Studies highlighting the critical role of this signaling circuitry in the Bordetella infectious cycle have focused on planktonically growing bacterial cells. It is becoming increasingly clear that the major mode of bacterial existence in the environment and within the body is a surface-attached state known as a biofilm. Biofilms are defined as consortia of sessile microorganisms that are embedded in a matrix. During routine growth of Bordetella under agitating conditions, we noticed the formation of a bacterial ring at the air-liquid interface of the culture tubes. We show here that this surface adherence property reflects the ability of these organisms to form biofilms. Our data demonstrate that the BvgAS locus regulates biofilm development in Bordetella. The results reported in this study suggest that the Bvg-mediated control in biofilm development is exerted at later time points after the initial attachment of bacteria to the different surfaces. Additionally, we show that these biofilms are highly tolerant of a number of antimicrobials, including the ones that are currently recommended for treatment of veterinary and human infections caused by Bordetella spp. Finally, we discuss the significance of the biofilm lifestyle mode as a potential contributor to persistent infections.     

Bordetella pertussis, molecular pathogenesis under multiple aspects

Recent studies, including those based on genomics, have demonstrated that besides toxins and adhesins, Bordetella pertussis uses many additional virulence determinants. Most of them are part of the BvgAS regulon, although some, in particular iron-uptake systems, are independent of BvgAS. They are regulated by iron, although in one case, the production of a siderophore receptor could be linked to the BvgAS regulon.     

Rational design of inhibitors of VirA-VirG two-component signal transduction

VirA-VirG two-component system regulates the vir (virulence) operon in response to specific host factors (xenognosins) in the plant pathogen Agrobacterium tumefaciens. Using whole cell assays, stable inhibitors inspired by the labile natural benzoxazinone inhibitor HDMBOA are developed. It is found that aromatic aldehydes represent a minimal structural unit for activity. In particular, 3-hydroxy-4,6-dimethoxy-3H-isobenzofuran-1-one (HDI) was found to have the highest activity, making it the most potent developed inhibitor of virulence gene expression in Agrobacterium.     

结核分枝杆菌PhoP系统研究进展

Pho P与Pho R组成的Pho PR是结核分枝杆菌重要的双组分调节系统。Pho P作为应答调节子调节基因的表达,这些基因参与细胞壁脂质合成,并对结核分枝杆菌毒力有重要调控作用。本文综述了Pho P的结构、性质以及相关的结核分枝杆菌疫苗研发情况,并提出了未来可能的研究趋势。