Biophysical and functional characterization of the Escherichia coli Dr fimbrial envelope reveals its importance for...

Uropathogenic Escherichia coli strains rely on specialized surface appendages to colonize the urinary tract, including Dr fimbriae, which are strongly associated with recurrent infection and long-term persistence. Although traditionally described as receptor-binding fibers, their broader contribution to bacterial surface architecture and physicochemical behavior has remained unclear. Here, combining quantitative proteomics, computational modeling, rheology, surface physicochemistry, and flow-based adhesion assays, we show that Dr fimbriae collectively form a dense, highly hydrated amphipathic envelope surrounding the bacterial cell. Rather than functioning as isolated filaments, they generate a dynamic supramolecular layer approximately 200-300 nm thick that markedly alters whole-cell properties. Mechanistic analyses performed in a simplified laboratory model were validated in the clinical UPEC strain IH11128, demonstrating that the principal physicochemical and adhesive properties of the Dr envelope are preserved despite phase-variable fimbrial expression. The Dr envelope strongly enhanced adhesion to abiotic surfaces, particularly hydrophilic glass, where Dr-positive bacteria resisted nanonewton-range capillary detachment forces, indicating stable multipoint anchoring. The envelope also promoted selective binding to calcium oxalate (CaOx), the principal mineral component of kidney stones, under urinary conditions. In the clinical isolate, CaOx binding occurred almost exclusively within the Dr-positive subpopulation and was largely abolished by anti-Dr antibodies, demonstrating that mineral recognition depends specifically on Dr fimbriae. Beyond adhesion, the fimbrial mesh functioned as a size-selective molecular filter. Dr-positive bacteria showed markedly reduced susceptibility to large bacteriophages, whereas infection by smaller phages and susceptibility to low-molecular-weight antibiotics remained unchanged, indicating steric exclusion of large biological particles without restricting diffusion of small solutes. Together, these findings establish the Dr envelope as a multifunctional supramolecular surface architecture that governs bacterial surface physicochemistry, promotes stable urinary tract colonization, mediates CaOx recognition, and expands the adaptive capabilities of UPEC within the urinary tract.