CSP-mediated QS circuit of S. mutans. The CSP pro-peptide, ComC, is processed and secreted by the dedicated ABC transporter (ComAB) as 21-CSP, which is further cleaved by a membrane protease, SepM, to form the active 18-CSP signal. 18-CSP interacts with the cognate transmembrane histidine-kinase receptor ComD, leading to phosphorylation of ComE, a response regulator, and results in autoinduction of the QS circuitry, the production of bacteriocins, and expression of comX, which codes for additional QS-regulated phenotypes.