Differential Regulation of Genes following Binding to Mannose Receptors.

Regulation of the uropathogenic (UPEC) and genes was examined following type 1 pili binding to mannose-coated Sepharose beads. Within 25 min after mannose attachment, expression dropped eightfold, whereas transcription increased about two- to fourfold. Because both genes encode site-specific recombinases that affect the position of the element containing the promoter, the positioning of was also examined. The element changed to slightly more Phase-OFF in bacteria mixed with plain beads, whereas UPEC cells interacting with mannose-coated beads had significantly less Phase-OFF orientation of under pH 7 conditions. On the other hand, Phase-OFF oriented increased fourfold when UPEC cells were mixed with plain beads in a pH 5.5 environment. Positioning of was also affected by mutations, demonstrating that the FimH ligand binding to its receptor facilitates the changes. Moreover, enzyme immunoassays showed that UPEC cells had greater type 1 pili expression when mixed with mannose-coated beads versus plain beads. These results indicate that, after type 1 pilus binding to tethered mannose receptors, the physiology of the cells changes to maintain the expression of type 1 pili even when awash in an acidic environment.