CcpA-Mediated Carbon Catabolite Repression of Virulence in the Group A Streptoccus

Abstract

The group A streptococcus (GAS) is a strict human pathogen, which causes a broad spectrum of diseases ranging from the self-limiting diseases such as pharyngitis and impetigo to the more severe invasive disease such as necrotizing fasciitis. The coordinate expression of a wide array of virulence factors in response to the changing host environment represents a key step in the ability of the GAS to mediate disease in the human host. The present study investigates the role of the primary mediator of sugar metabolism regulation, carbon catabolite control protein (CcpA), in the regulation of virulence of the GAS. A putative CcpA-binding site or catabolite response element (cre) was identified upstream of the promoter for the virulence gene regulator, Mga. CcpA was shown to specifically bind to this cre, and activate the transcription of mga. In addition, both transcription of mga and expression of Mga were reduced in a ccpA mutant strain; however, the expression of the Mga-regulated genes were not affected. Additional studies analyzing the role of CcpA in pathogenesis of the GAS, showed a "hypervirulent" phenotype in the absence of CcpA using two mouse infection models. Microarray analysis of the delta ccpA strain determined that CcpA significantly represses the expression of saga, the gene encoding the potent cytolysin, streptolysin S (SLS). Moreover, hemolytic activity due to SLS was increased in the delta ccpA strain, and expression from Psaga demonstrated strong catabolite repression during growth in glucose compared to sucrose. Furthermore, purified GAS CcpA was shown to bind directly to the cre present in Psaga. The role of SLS in the increased pathogenesis of the delta ccpA strain was investigated by the creation of a double mutant strain, which lacks the ability to secrete SLS. Importantly, systemic infection of mice with the delta ccpA sagB double mutant resulted in complete attenuation of virulence and determined that the increased SLS expression is responsible for the "hypervirulent" phenotype in the absence of CcpA. Overall, these results have demonstrated a strong link between sugar metabolism regulation and virulence gene expression in the GAS.