Differential Regulation ofEscherichia coli fimGenes following Binding to Mannose Receptors

Abstract

Regulation of the uropathogenicEscherichia coli(UPEC)fimBandfimEgenes was examined following type 1 pili binding to mannose-coated Sepharose beads. Within 25 min after mannose attachment,fimEexpression dropped eightfold, whereasfimBtranscription increased about two- to fourfold. Because bothfimgenes encode site-specific recombinases that affect the position of thefimSelement containing thefimApromoter, the positioning offimSwas also examined. ThefimSelement 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 offimSunder pH 7 conditions. On the other hand, Phase-OFF orientedfimSincreased fourfold when UPEC cells were mixed with plain beads in a pH 5.5 environment. Positioning offimSwas also affected byfimHmutations, 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 theE. colicells changes to maintain the expression of type 1 pili even when awash in an acidic environment.