FIG 8.

Model for three c-di-GMP states in V. cholerae. Our results suggest that the regulatory network controlled by c-di-GMP in V. cholerae can be simplified to three states. Top, status of the tfoY transcripts; bottom, state of the cells and other regulatory factors. At low c-di-GMP concentrations, TfoY expression is high due to the Vc2 riboswitch being unbound in the P₁ and P₂ transcripts, and FlrA transcriptional activation is maximal, leading to dispersive motility. At intermediate c-di-GMP concentrations, TfoY is poorly expressed, as Vc2 is bound to c-di-GMP in the P₁ and P₂ transcripts, but FlrA retains some ability to induce transcription of the flagellar biosynthesis genes, resulting in dense motility. At high c-di-GMP concentrations, the VPS genes are induced, driving biofilm formation and inhibiting motility. FlrA is unable to induce transcription due to c-di-GMP binding. VpsR induces transcription of the P₃ and P₄ transcripts, leading to intermediate expression of TfoY, but it cannot induce motility due to VPS production and FlrA inhibition.