Defects in Ex Vivo and in Vivo Growth and Sensitivity to Osmotic Stress of Group A Streptococcus Caused by Interruption of Response Regulator Gene VicR

The regulator VicR of the two-component regulatory system VicRK is essential in several Gram-positive bacteria. However, the authors were able to generate an unconditional vicR insertional mutant of group A Streptococcus. This mutant grew well in rich media but not in non-immune human blood and serum, had attenuated virulence, and was unstable in mice. Complementation of the mutant with vicR expressed in trans restored its phenotype to wild-type. A vicK deletion mutant had a phenotype similar to that of the vicR mutant. Phagocytosis and killing of the vicR mutant were normal, suggesting that VicRK does not regulate processes involved in evasion of host defence. Microarray analysis showed that vicR inactivation down-regulated the transcription of 13 genes, including putative cell wall hydrolase gene pcsB and spy1058-1060, which encode a putative phosphotransferase system enzyme II for carbohydrate transport, and upregulated the expression of five genes, including spy0183 and spy0184, which encode an osmoprotectant transporter OpuA. Consistent with microarray analysis, the vicR mutant took up more of the osmoprotectants betaine and proline and was sensitive to osmotic stress, indicating that vicR inactivation induced osmotic stress and increased susceptibility to osmotic pressure. Additionally, a spy1060 deletion mutant also displayed attenuated virulence. These results suggest that VicRK regulates processes involved in cell wall metabolism, nutrient uptake, and osmotic protection.