Ectopic expression of the flagellar regulon alters development of the Bordetella-host interaction.

Signal transduction molecules within the two-component family represent a conserved adaptation for the control of genes involved in pathogenesis. The Bordetella virulence control locus, bvgAS, activates and represses gene expression in response to environmental signals. While infection requires virulence gene activation, the role of gene repression during infection is not understood. By altering regulatory genes and reversing regulatory connections, we found evidence that the BvgAS-repressed genes responsible for motility are neither required nor expressed during colonization of the host. Expression of this Bvg- phase-specific phenotype in the Bvg+ growth phase resulted in a defect in tracheal colonization. Therefore, BvgAS promotes virulence both by activating genes required for colonization and by repressing genes that inhibit the development of infection.