Pleiotropic functions of CpdB in Bacillus anthracis.

Bacillus anthracis is the causative agent of anthrax disease. Our prior research indicated that cyclic (c)-di-AMP accumulation attenuated bacterial virulence in mice. However, the function of c-di-AMP secretion and its regulatory mechanism in anthrax have not been revealed. We characterized the role of the ecto-nucleotidase CpdB in B. anthracis. CpdB exhibits phosphodiesterase activity towards c-di-AMP and 2'3'-cGMP-AMP, and nucleotidase activity towards several mononucleotides, including the preferred substrates c-di-AMP and pApA. Our results demonstrated that inactivation of cpdB altered purine nucleotide metabolism, decreasing the levels of anthrax toxins and extracellular proteases while increasing the expression of adhesion factor BslA. The rates of adhesion and invasion of B. anthracis to both endothelial cells and immune cells in vitro were enhanced by cpdB inactivation. In infected silkworms, cpdB inactivation led to higher levels of colonization in hemolymph, but virulence was attenuated. These findings suggest that cpdB has pleiotropic functions in the infection and virulence of B. anthracis.