Summary Cyclic diadenosine monophosphate (c‐di‐ AMP ) has been implicated in the control of many important bacterial activities. However, the function of this molecule in S treptococcus mutans , the primary aetiological agent of human dental caries, is unknown. In this study, we identified and characterized a diadenylate cyclase, named CdaA , in S . mutans . Furthermore, we showed that in‐frame deletion of the cdaA gene in S ....