FIG. 1.

Regulatory network of CsgD-mediated biofilm formation in S. Typhimurium UMR1. CsgD expression requires the stress sigma factor RpoS and the response regulator OmpR (34). CsgD is required for the expression of the csgBA operon, encoding structural subunits of curli fimbriae (19), and adrA, encoding a diguanylate cyclase required for the activation of cellulose biosynthesis, on agar plates (55). CsgD expression can be positively modulated by c-di-GMP, the steady-state level of which is determined by the activity of c-di-GMP-specific phosphodiesterases, such as STM1703 and diguanylate cyclases (23, 43).