Glutamate Limitation, BvgAS Activation, and (p)ppGpp Regulate the Expression of the Bordetella pertussis Type 3 Secretion System

Abstract

Bordetella pertussis is a bacterium that is considered to be highly adapted to humans, and it has not been isolated from the environment. As this bacterium does not utilize sugars, the abundant supply of glutamate in Stainer Scholte (SS) medium enables B. pertussis to grow efficiently in liquid culture in vitro, and as such, SS medium is a popular choice for laboratory experiments. However, the concentration of glutamate in the in vivo niche of B. pertussis is quite low. We investigated the bacterial response to low concentrations of glutamate to elucidate bacterial physiology via the expression of the type 3 secretion system (T3SS), and we discuss its relationship to the Bvg mode in which the two-component regulator of pathogenesis (BvgAS) is activated. Glutamate limitation induced the expression of both the T3SS apparatus and effector genes at the transcriptional level. (p)ppGpp, a modulator of the stringent response, was necessary for maximum expression of the T3SS genes. These observations indicate that the expression of the T3SS is managed by nutrient starvation. In addition, the autoaggregation ability was high in the absence of glutamate and no autoaggregation was observed in glutamate-replete medium. Taken together, glutamate-limited conditions in Bvg ؉ mode elicit the high expression of T3SS genes in B. pertussis and promotes its sessile form. IMPORTANCEBordetella pertussis is a highly contagious pathogen that causes respiratory infectious disease. In spite of the increasing use of vaccination, the number of patients with pertussis is increasing. The proteins produced in vivo often are different from the protein profile under laboratory conditions; therefore, the development of conditions reflecting the host environment is important to understand native bacterial behavior. In the present study, we examined the effect of glutamate limitation, as its concentration in vivo is much lower than that in the culture medium currently used for B. pertussis experiments. As predicted, the T3SS was induced by glutamate limitation. These results are suggestive of the importance of regulation by nutrient conditions and in the pathogenicity of B. pertussis.

The stringent response regulator (p) ppGpp mediates virulence gene expression and survival in Erwinia amylovora

“…Down-regulation of the T3SS genes, accompanied by attenuated virulence and reduced growth, was also reported in the P. syringae (p) ppGpp 0 mutants [16]. Similar results were also reported in Bordetella pertussis in response to glutamine limitation [29] and in E. coli in response to nutrient starvation [15]. Previous studies have demonstrated that the T3SS gene expression in E. amylovora reached the highest level at 6 hpi in HMM [23].…”

Proteomic Adaptation of Australian Epidemic Bordetella pertussis

“…Upregulation of BP3831 may lead to greater acquisition of glutamate where it is limited in the respiratory tract, therefore enhancing metabolic efficiency and fitness. It has also been found that low levels of glutamate leads to higher expression of the T3SS, therefore decreased T3SS expression in L1423 may also be linked to greater acquisition of glutamate.…”

The BvgAS Regulon of Bordetella pertussis

“…However, the importance of the T3SS in B. pertussis has not been clear. Although some previous work had failed to detect T3SS proteins in B. pertussis and concluded that the T3SS may be inactive (46), other work has challenged this idea by demonstrating that clinical isolates and laboratory-adapted B. pertussis strains under certain nutrition-limited cultures produce T3SS proteins (50). In addition, Ahuja et al (32) recently reported that in both B. pertussis and B. bronchiseptica, BtrA (BP2233) functions as an anti-sigma factor for BrpL, the ECF sigma factor responsible for T3SS expression.…”