Determination of the Regulon of CcpA, a pleiotropic regulator, in the pathogen Streptococcus agalactiae
Résumé
Streptococcus agalactiae is responsible for various infections in a wide variety of hosts. This shows its ability to acquire nutrients in variable conditions. The carbon catabolite repression allows bacteria to prioritize the uptake and the catabolism of the environmental sugars. In Gram-positive bacteria, CcpA (catabolite control protein A), a pleiotropic transcriptional regulator, plays a key role in catabolite repression. CcpA binds to a specific DNA consensus sequence named « cre » (for catabolite response element) in the regulatory region of the target genes, thereby causing their activation or repression. The goal of this study is to determine the regulon and the role(s) of CcpA in the physiology and adaptation of S. agalactiae. We studied the effect of CcpA deletion in S.agalactiae by comparing, with an RNAseq analysis, the global transcription of the WT and ∆ccpA strains. In order to determine the direct targets of CcpA, we searched the genes harbouring a putative cre site in the S.agalactiae genome with an in-silico approach. We are validating the consensus cre sequence with gelshift experiments. We showed that 13.5% of the S. agalactiae genome was regulated by CcpA and that it acts mostly as a repressor. Among the 274 genes significantly regulated by CcpA, 79 have at least one cre site. In-silico and RNAseq analysis highlight the CcpA direct regulation of genes coding proteins putatively involved in acidic and oxidative stresses. We are constructing transcriptional fusion vectors in order to confirm the implication of CcpA in their regulation and their expression in stress responses, and therefore the role of this regulator in the adaptation of S. agalactiae.