Multiple co-regulatory elements and IHF are necessary for the control of fimB expression in response to sialic acid and N-acetylglucosamine in Escherichia coli K-12

Expression of the FimB recombinase, and hence the OFF-to-ON switching of type 1 fimbriation in Escherichia coli, is inhibited by sialic acid (Neu₅Ac) and by GlcNAc. NanR (Neu₅Ac-responsive) and NagC (GlcNAc-6P-responsive) activate fimB expression by binding to operators (ONR and ONC₁ respectively) located more than 600 bp upstream of the fimB promoter within the large (1.4 kb) nanC-fimB intergenic region. Here it is demonstrated that NagC binding to a second site (ONC₂), located 212 bp closer to fimB, also controls fimB expression, and that integration host factor (IHF), which binds midway between ONC₁ and ONC₂, facilitates NagC binding to its two operator sites. In contrast, IHF does not enhance the ability of NanR to activate fimB expression in the wild-type background. Neither sequences up to 820 bp upstream of ONR, nor those 270 bp downstream of ONC₂, are required for activation by NanR and NagC. However, placing the NanR, IHF and NagC binding sites closer to the fimB promoter enhances the ability of the regulators to activate fimB expression. These results support a refined model for how two potentially key indicators of host inflammation, Neu₅Ac and GlcNAc, regulate type 1 fimbriation.