VirS, an OmpR/PhoB subfamily response regulator, is required for activation of vapA gene expression in Rhodococcus equi

BACKGROUND: Rhodococcus equi is an important pulmonary pathogen in foals and in immunocompromised individuals. Virulent R. equi strains carry an 80-90 kb virulence plasmid that expresses the virulence-associated protein A (VapA). VapA expression is regulated by temperature and pH. The LysR-type transcriptional regulator, VirR, is involved in the regulation of the vapA gene. To examine the mechanism underlying transcriptional regulation of vapA, we characterized an R. equi mutant in which another putative transcriptional regulator encoded on the virulence plasmid, VirS, was deleted. RESULTS: Deletion of virS reduced vapA promoter activity to non-inducible levels. Complementary expression of VirS in the virS deletion mutant restored transcription at the P(vapA) promoter, even under non-inducing conditions (30°C and pH 8.0). In addition, VirS expression increased P(vapA) promoter activity in the absence of functional VirR. Further, transcription of the icgA operon containing virS was regulated by pH and temperature in the same manner as vapA. CONCLUSIONS: This study suggests that VirS is required for VapA expression and that regulation of P(vapA)-promoter activity may be achieved by controlling VirS expression levels. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s12866-014-0243-1) contains supplementary material, which is available to authorized users.