Catalyzes the synthesis of cyclic-di-GMP (c-di-GMP) via the condensation of 2 GTP molecules (PubMed:25809128). Cyclic-di-GMP is a second messenger which controls cell surface-associated traits in bacteria (PubMed:25118352). Localizes at the cell poles through interaction with FimV where it increases the local pools of c-di-GMP (By similarity). 2 GTP = cyclic di-3',5'-guanylate + 2 diphosphate Binds 1 Mg(2+) ion per monomer. Purine metabolism; 3',5'-cyclic di-GMP biosynthesis. Homodimer. Localizes at the cell poles in a FimV-dependent manner. The GGEEF domain is required for function. Deletion mutant leads to a reduction in virulence that is reflected by decreased bacterial dissemination, enhanced bacterial clearance and reduced host lung injury. It also results in increased swimming motility of approximatly 1.5-fold increase, and a 2-fold decrease in biofilm formation.