BVGAS IS SUFFICIENT FOR ACTIVATION OF THE BORDETELLA-PERTUSSIS PTX LOCUS IN ESCHERICHIA-COLI

BvgA and BvgS, which regulate virulence gene expression in Bordetella pertussis, are members of the two-component signal transduction family . The effects of growth conditions on the ability of BvgAS to activate transcription of fhaB (encoding filamentous hemagglutinin) and ptxA ( encoding the S1 subunit of pertussis toxin) were assessed in Escherich ia coli by using chromosomal fhaB-lacZYA and ptxA-lacZYA fusions. Alth ough it had previously been reported that a ptxA-lacZYA transcriptiona l fusion was not activated by bvgAS in E. coli (J, F. Miller, C. R. Ro y, and S, Falkow, J. Bacteriol. 171:6345-6348, 1989), we now present e vidence that ptxA is activated by bvgAS in E. coli in a manner that is highly dependent on the growth conditions. Higher levels of P-galacto sidase were produced by ptxA-lacZYA in the presence of bvgAS during gr owth in Stainer-Scholte medium or M9 minimal salts medium with glucose than in Luria-Bertani medium. In contrast, the level of fhaB-lacZYA e xpression was high during growth in all media. Addition of modulating stimuli which inhibit BvgAS function eliminated expression of ptxA-lac ZYA. Levels of beta-galactosidase expressed from the ptx-lacZYA fusion correlated with growth rate and with the final optical density at 600 nm, suggesting that the lower growth rate in M9-glucose and Stainer-S cholte media was responsible for greater accumulation of beta-galactos idase than was seen in Luria-Bertani medium. Overproduction of BvgA wa s not sufficient for activation of ptxA expression but was sufficient for fhaB expression. However, overproduction of a constitutive BvgA al lele (bvgA-C1) or overproduction of BvgA in the presence of BvgS was a ble to activate ptxA. Our results demonstrate Bvg-dependent activation of a ptxA-lacZYA fusion in E. coli and indicate that bvg is the only Bordetella locus required for ptxA activation in this heterologous sys tem.