Diguanylate cyclase (DGC) that catalyzes the synthesis of cyclic diguanylate (c-di-GMP) via the condensation of 2 GTP molecules. Is involved in the modulation of intracellular c-di-GMP levels. Cyclic-di-GMP is a second messenger which positively regulates biofilm formation and negatively regulates virulence in V.cholerae, and is proposed to play an important role in the transition from persistence in the environment to survival in the host. Overexpression of vdcA results in increased biofilm formation, and reduced motility and virulence. 2 GTP = cyclic di-3',5'-guanylate + 2 diphosphate Binds 1 Mg(2+) ion per subunit. Purine metabolism; 3',5'-cyclic di-GMP biosynthesis.