CidR and CcpA synergistically regulate Staphylococcus aureus cidABC expression.

The death and lysis of a subpopulation of Staphylococcus aureus cells during biofilm development benefit the whole bacterial population through the release of an important component of the biofilm matrix, extracellular DNA. Previously we have demonstrated that these processes are affected by the gene products of cidABC operon, the expression of which is controlled by the LysR-type transcriptional regulator, CidR. In this study, we characterized cis- and trans-acting elements essential for the induction of the cidABC operon. In addition to a CidR-binding site located within the cidABC promoter region, sequence analysis revealed the presence of a putative catabolite responsive element (cre-box), suggestive of the involvement of the catabolite control protein A (CcpA) in the regulation of cidABC expression. This was confirmed using electrophoretic mobility-shift assays and real-time reverse transcriptase PCR analysis demonstrating the direct positive control of cidABC transcription by the master regulator of carbon metabolism. Furthermore, the importance of CcpA and identified cre-site for the induction of the cidABC operon was demonstrated by examining the expression of PcidABC-lacZ reporter fusions in various mutant strains in which the genes involved in carbon metabolism and carbon catabolite repression were disrupted. Together the results of this study demonstrate the necessity of both transcriptional regulators, CidR and CcpA, for the induction of the cidABC operon and revealed the complexity of molecular interactions controlling its expression. Importance This work focuses on characterization of cis- and trans-acting elements essential for the induction of the cidABC operon in S. aureus. The results of this study are the first to demonstrate the synergistic control of cidABC expression by transcriptional regulators CidR and CcpA during carbohydrate metabolism. We established that the full induction of cidABC expression depends on the metabolic state of bacteria and requires both CidR and CcpA. Together, these findings delineate regulatory control of cidABC expression under different metabolic conditions and provide important new insights into understanding of the cell death mechanisms during biofilm development in S. aureus.