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Osmolarity affects Bvg-mediated virulence regulation by Bordetella pertussis

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Bordetella pertussis dramatically alters its phenotype by sensing its environment via the BvgAS regulatory system. Increased concentrations of specific chemicals are used in vitro to induce modulation of the bacterium from the Bvg+ virulent phenotype to a fully Bvg phenotype. Varied expression of sets of Bvg-regulated molecules depends on the modulating capacity of the environment. We examined the effect of a number of chemicals on the modulating capacity of B.pertussis growth media, both alone and in combination with known modulators. It was demonstrated that under certain conditions the Bvg-intermediate protein, BipA, is coexpressed with the Bvg antigen, VraA. This demonstrates that the patterns of molecules expressed in the different phenotypes of B.pertussis are more fluid than has previously been demonstrated. The in vitro modulator, sulfate, was found to be a relatively inefficient modulator of our Tohama I-derived B.pertussis strain. However, addition of nicotinic acid, MgCl2, or sucrose in combination with relatively low sulfate concentrations resulted in effective modulation. This suggests that multiple signals may affect modulation through the BvgAS system or possibly through other regulatory networks. In addition, the cooperative modulating effect of sucrose implicates osmolarity as an environmental stimulus that affects phenotypic modulation.

Bordetella pertussis affecte de façon importante son phénotype en sondant son environnement à l’aide du système de régulation BvgAS. Des concentrations croissantes de composés chimiques spécifiques sont utilisées in vitro pour induire la modulation de la bactérie d’un phénotype Bvg+ virulent en un phénotype totalement Bvg. Les niveaux d’expression d’un groupe de molécules régulées par Bvg dépendent de la capacité de modulation de l’environnement. Nous avons examiné l’effet d’un certain nombre de composés chimiques utilisés seuls ou en présence de modulateurs connus, sur la capacité de modulation d’un milieu de croissance de B. pertussis. Sous certaines conditions, la protéine intermédiaire de Bvg, BipA est co-exprimée avec l’antigène Bvg, VraA. Ceci démontre que les patrons de molécules exprimées par les différents phénotypes de B.pertussis sont plus souples que ce que l’on croyait initialement. Un modulateur in vitro, le sulfate, s’est révélé relativement inefficace chez notre souche de B. pertussis dérivée de Tohama I. Cependant, l’ajout d’acide nicotinique, de MgCl2 ou de sucrose en combinaison avec des concentrations relativement faibles de sulfate a résulté en une modulation efficace. Ceci suggère que de multiples signaux peuvent affecter la modulation à travers le système BvgAS ou possiblement à travers d’autres systèmes régulateurs. De plus, la modulation coopérative observée avec le sucrose suggère que l’osmolarité soit impliquée en tant que stimulus environnemental qui affecte la modulation phénotypique.

Document Type: Research Article

Publication date: 2007-09-01

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  • Published since 1954, this monthly journal contains new research in the field of microbiology including applied microbiology and biotechnology; microbial structure and function; fungi and other eucaryotic protists; infection and immunity; microbial ecology; physiology, metabolism and enzymology; and virology, genetics, and molecular biology. It also publishes review articles and notes on an occasional basis, contributed by recognized scientists worldwide.
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