Cyclic di‐AMP mediates biofilm formation

Summary Cyclic di‐ AMP (c‐di‐ AMP ) is an emerging second messenger in bacteria. It has been shown to play important roles in bacterial fitness and virulence. However, transduction of c‐di‐ AMP signaling in bacteria and the role of c‐di‐ AMP in biofilm formation are not well understood. The level of c‐di‐ AMP is modulated by activity of di‐adenylyl cyclase that produces c‐di‐ AMP and phosphodiesterase ( PDE ) that degrades c‐di‐ AMP . In this study, we determined that increased c‐di‐ AMP levels by deletion of the pdeA gene coding for a PDE promoted biofilm formation in S treptococcus mutans . Deletion of pde A upregulated expression of gtf B , the gene coding for a major glucan producing enzyme. Inactivation of gtf B blocked the increased biofilm by the pde A mutant. Two c ‐di‐ A MP b inding p roteins including CabPA ( SMU _1562) and CabPB ( SMU _1708) were identified. Interestingly, only CabPA deficiency inhibited both the increased biofilm formation and the upregulated expression of GtfB observed in the pdeA mutant. In addition, CabPA but not CabPB interacted with VicR , a known transcriptional factor that regulates expression of gtf B , suggesting that a signaling link between CabPA and GtfB through VicR . Increased biofilm by the pde A deficiency also enhanced bacterial colonization of D rosophila in vivo . Taken together, our studies reveal a new role of c‐di‐ AMP in mediating biofilm formation through a CabPA / VicR / GtfB signaling network in S . mutans .