Comparative analysis of the virulence control systems of Bordetella pertussis and Bordetella bronchiseptica

Abstract

Bordetella pertussis and Bordetella bronchiseptica contain nearly identical BvgAS signal-transduction systems that mediate a biphasic transition between virulent (Bvg+) and avirulent (Bvg-) phases. In the Bvg+ phase, the two species express a similar set of adhesins and toxins, and in both organisms the transition to the Bvg- phase occurs in response to the same environmental signals (low temperature or the presence of nicotinic acid or sulphate anion). These two species differ, however, with regard to Bvg(-)-phase phenotypes, host specificity, the severity and course of the diseases they cause, and also potentially in their routes of transmission. To investigate the contribution of the virulence-control system to these phenotypic differences, we constructed a chimeric B. bronchiseptica strain containing bvgAS from B. pertussis and compared it with wild-type B. bronchiseptica in vitro and in vivo. The chimeric strain was indistinguishable from the wild type in its ability to express Bvg(+)- and Bvg(-)- phase-specific factors. However, although the chimeric strain responded to the same signals as the wild type, it differed dramatically in sensitivity to these signals; significantly more nicotinic acid or MgSO4 was required to modulate the chimeric strain compared with the wild-type strain. Despite this difference in signal sensitivity, the chimeric strain was indistinguishable from the wild type in its ability to cause respiratory-tract infections in rats, indicating that the bvgAS loci of B. pertussis and B. bronchiseptica are functionally interchangeable in vivo. By exchanging discrete fragments of bvgAS, we found that the periplasmic region of BvgS determines signal sensitivity.

A Novel Sensor Kinase Is Required for Bordetella bronchiseptica To Colonize the Lower Respiratory Tract

“…Bacteria harboring chromosomal lacZ gene fusions were grown for 16 h in SS broth. Cells were permeabilized by the addition of 0.1% sodium dodecyl sulfate (SDS) and chloroform, and ␤-galactosidase activity was measured as previously described (40). Optical density (OD) measurements were taken using a Multiskan EX plate reader (ThermoFisher Scientific, Waltham, MA).…”

“…Whole-cell or supernatant proteins were harvested from overnight-grown wild-type and mutant B. bronchiseptica (optical density at 600 nm, between 2 and 3) as described previously (31,40). Briefly, whole-cell proteins were harvested by boiling cells that had been resuspended in 0.1% SDS.…”

“…For pathogenic bacteria, TCSs play key roles in modulating gene expression during infection (7,18,34,48,63). Despite differences in host range, B. pertussis and B. bronchiseptica produce a functionally interchangeable BvgAS TCS that is necessary for colonization of the respiratory tract (11,12,40) and that has been shown to control at least three phenotypic phases during growth in vitro. At 37°C and in the relative absence of sulfate ions and nicotinic acid, the BvgAS system is active (the Bvg ϩ phase) and induces the expression of genes necessary for virulence, such as those required for adherence to host tissues and modulation of the immune response, while simultaneously repressing the expression of genes detrimental to virulence, such as those encoding flagella (1,4,40).…”

“…Despite differences in host range, B. pertussis and B. bronchiseptica produce a functionally interchangeable BvgAS TCS that is necessary for colonization of the respiratory tract (11,12,40) and that has been shown to control at least three phenotypic phases during growth in vitro. At 37°C and in the relative absence of sulfate ions and nicotinic acid, the BvgAS system is active (the Bvg ϩ phase) and induces the expression of genes necessary for virulence, such as those required for adherence to host tissues and modulation of the immune response, while simultaneously repressing the expression of genes detrimental to virulence, such as those encoding flagella (1,4,40). When Bordetella cells are grown at 25°C or 37°C in the presence of mM concentrations of sulfate ions or nicotinic acid, BvgAS is inactive (the Bvg Ϫ phase), resulting in the lack of virulence gene expression and concomitant expression of Bvg-repressed genes.…”

“…This is perhaps not surprising, since coordinating the appropriate patterns of gene expression during the course of infection often requires the activity of multiple TCSs that respond to different signals encountered within the host environment (18-20, 22, 48). In Bordetella, the BvgAS TCS has been extensively characterized as the master regulator of virulence, as it controls the expression of virtually all known genes that contribute to the ability of the bacteria to colonize and persist in the host, including genes encoding adhesins (e.g., FHA, fimbriae, and pertactin) and toxins (e.g., pertussis toxin, CyaA, and type III secretion effectors) (10,40,41,43,45). More recently, a second TCS, risAS, that contributes to the ability of B. bronchiseptica to resist oxidative stress and colonize the mouse respiratory tract was identified (33,61,71).…”