Abstract
Agar plate-based biofilm of enterobacteria like Escherichia coli is characterized by expression of the extracellular matrix components amyloid curli and cellulose exopolysaccharide, which can be visually enhanced upon addition of the dye Congo Red, resulting in a red, dry, and rough (rdar) colony morphology. Expression of the rdar morphotype depends on the transcriptional regulator CsgD and occurs predominantly at ambient temperature in model strains. In contrast, commensal and pathogenic isolates frequently express the csgD-dependent rdar morphotype semi-constitutively, also at human host body temperature. To unravel the molecular basis of temperature-independent rdar morphotype expression, biofilm components and c-di-GMP turnover proteins of seven commensal and uropathogenic E. coli isolates were analyzed. A diversity within the c-di-GMP signaling network was uncovered which suggests alteration of activity of the trigger phosphodiesterase YciR to contribute to (up)regulation of csgD expression and consequently semi-constitutive rdar morphotype development.