Catalyzes the condensation of 2 ATP molecules into cyclic di-AMP (c-di-AMP), a signaling compound secreted into the host's cytosol where it triggers the cytosolic surveillance pathway (CSP), a host pathway of innate immunity characterized by expression of beta interferon (IFN-beta) and coregulated genes (Probable). Overexpression increases export of c-di-AMP (PubMed:23716572). c-di-AMP is a second messenger that mediates growth, cell wall stability and virulence (Probable). 2 ATP = 3',3'-c-di-AMP + 2 diphosphate Probably a homodimer. Essential, it cannot be deleted; in depletion experiments doubling time increases from 44 to 84 minutes, cells have decreased export of c-di-AMP, increased susceptibility to the antibiotic cefuroxime, a weakened cell wall, 10-fold lower growth in host macrophages, are about 10(3) less virulent in mice and more susceptible to in-host bacteriolysis (PubMed:23716572). In a viable dacA-relA-relP-relQ deletion mutant about 2-fold decreased intracellular levels of c-di-AMP (PubMed:25965978). Belongs to the adenylate cyclase family. DacA/CdaA subfamily.