Altered Regulation of the Diguanylate Cyclase YaiC Reduces Production of Type 1 Fimbriae in a Pst Mutant of Uropathogenic Escherichia coli CFT073

Thepst gene cluster encodes the phosphate-specific transport (Pst) system. Inactivation of the Pst system constitutively activates the two-component regulatory system PhoBR and attenuates the virulence of pathogenic bacteria. In uropathogenicEscherichia coli strain CFT073, attenuation by inactivation ofpst is predominantly attributed to the decreased expression of type 1 fimbriae. However, the molecular mechanisms connecting the Pst system and type 1 fimbriae are unknown. To address this, a transposon library was constructed in thepst mutant, and clones were tested for a regain in type 1 fimbrial production. Among them, the diguanylate cyclase encoded byyaiC (adrA inSalmonella ) was identified to connect the Pst system and type 1 fimbrial expression. In thepst mutant, the decreased expression of type 1 fimbriae is connected by the induction ofyaiC . This is predominantly due to altered expression of the FimBE-like recombinase genesipuA andipbA , affecting at the same time the inversion of thefim promoter switch (fimS ). In thepst mutant, inactivation ofyaiC restoredfim -dependent adhesion to bladder cells and virulence. Interestingly, the expression ofyaiC was activated by PhoB, since transcription ofyaiC was linked to the PhoB-dependentphoA-psiF operon. As YaiC is involved in cyclic di-GMP (c-di-GMP) biosynthesis, an increased accumulation of c-di-GMP was observed in thepst mutant. Hence, the results suggest that one mechanism by which deletion of the Pst system reduces the expression of type 1 fimbriae is through PhoBR-mediated activation ofyaiC , which in turn increases the accumulation of c-di-GMP, represses thefim operon, and, consequently, attenuates virulence in the mouse urinary tract infection model.IMPORTANCE Urinary tract infections (UTIs) are common bacterial infections in humans. They are mainly caused by uropathogenicEscherichia coli (UPEC). We previously showed that interference with phosphate homeostasis decreases the expression of type 1 fimbriae and attenuates UPEC virulence. Herein, we identified that alteration of the phosphate metabolism increases production of the signaling molecule c-di-GMP, which in turn decreases the expression of type 1 fimbriae. We also determine the regulatory cascade leading to the accumulation of c-di-GMP and identify the Pho regulon as new players in c-di-GMP-mediated cell signaling. By understanding the molecular mechanisms leading to the expression of virulence factors, we will be in a better position to develop new therapeutics.