Catalyzes the synthesis of cyclic-di-GMP (c-di-GMP) via the condensation of 2 GTP molecules (PubMed:18713317, PubMed:19460094, PubMed:20582742). May act as a zinc sensor that controls, via c-di-GMP, post-translational events (PubMed:23769666). Overexpression leads to a strong repression of swimming; swimming returnes to normal when residues 206-207 are both mutated to Ala. Overexpression also leads to a reduction in flagellar abundance and a 20-fold increase in c-di-GMP levels in vivo. Required for aminoglycoside-mediated induction of biofilm formation, it also plays a lesser role in biofilm production in response to other classes of translation inhibitors. The c-di-GMP produced by this enzyme up-regulates poly-GlcNAc production as well as the biofilm synthesis protein PgaD, although c-di-GMP is probably not the main inducing principle. C-di-GMP is a second messenger which controls cell surface-associated traits in bacteria (PubMed:19460094). 2 GTP = cyclic di-3',5'-guanylate + 2 diphosphate Binds 1 Mg(2+) ion per monomer. Allosterically regulated by zinc, which seems to regulate the activity of the catalytic GGDEF domains by impeding their mobility and thus preventing productive encounter of the two GTP substrates (PubMed:23769666). Subject to product inhibition by c-di-GMP at a KI of 44 uM (PubMed:19460094). Optimum pH is 7.5. Purine metabolism; 3',5'-cyclic di-GMP biosynthesis. Homodimer. CsrA binds to the mRNA and reduces its levels. Expressed at low levels at both 28 and 37 degrees Celsius. Repressed by RpoS. Contains an N-terminal CZB (chemoreceptor zinc binding) domain and a C-terminal GGDEF domain. A slight increase in motility. No visible effect on curli production (PubMed:18713317). Decreased biofilm formation, very little associated poly-GlcNAc production, and a complete loss of aminoglycoside-mediated induction of biofilm formation (PubMed:19460094).