Figure 2.

Quorum sensing system in S. mutans and the inhibitory effects of natural products on this system. The CSP-ComDE system is composed of a signal peptide (CSP, encoded by ComC) and the ComDE two-component system. During the cell density increase, the accumulated CSP interacts with ComD (membrane-bound histidine kinase receptor) directly to cause the phosphorylation and activation of ComE (the cytoplasmic response regulator). The activated ComE regulates the gene expression of bacteriocin production and biofilm formation. The ComRS system consists of signaling peptide pheromone (XIP, encoded by ComS) and a transcriptional regulator (ComR). The XIP interacts with and activates ComR to regulate the expression of ComX, and thus switches the genes related to competence and persister formation. Rhodiola rosea inhibited ComDE gene expression and baicalin inhibited ComX gene expression.