THE BVGAS VIRULENCE CONTROL-SYSTEM REGULATES TYPE-III SECRETION IN BORDETELLA-BRONCHISEPTICA

The BvgAS signal transduction system in Bordetella spp. mediates a tra nsition between infectious (Bvg(+)) and non-infectious (Bvg(-)) phases by sensing environmental conditions and regulating gene expression. U sing differential display, arbitrary-primed polymerase chain reaction (PCR), we identified a gene expressed in the Bvg(+) phase of Bordetell a bronchiseptica that shows a high degree of sequence similarity to a locus involved in providing energy for type III secretion in pathogeni c Gram-negative bacteria (yscN in Yersinia spp.). We determined that t he expression of this homologue in B. bronchiseptica (designated bscN) is regulated by bvg. Several open reading frames surrounding the bscN locus also show sequence similarity to loci encoding type III secreti on apparatus components in other bacteria. An in-frame deletion of bsc N in B. bronchiseptica leads to decreased secretion of several protein s, decreased cytotoxicity towards cultured cell lines and a defect in causing tyrosine dephosphorylation of specific proteins in infected ce lls in vitro. The deletion strain also revealed that bscN-mediated sec retion is required for persistent colonization of the trachea in a rat infection model. Loci encoding type III secretion homologues were ide ntified in four strains of B. pertussis and two strains of B. parapert ussis. B. pertussis strain 18323 and an ovine isolate of B. parapertus sis show significant transcription of the genes in vitro.