Fast uncoiling kinetics of F1C pili expressed by uropathogenic Escherichia coli are revealed on a single pilus level using force-measuring optical tweezers

Abstract

Uropathogenic Escherichia coli (UPEC) express various kinds of organelles, so-called pili or fimbriae, that mediate adhesion to host tissue in the urinary tract through specific receptor-adhesin interactions. The biomechanical properties of these pili have been considered important for the ability of bacteria to withstand shear forces from rinsing urine flows. Force-measuring optical tweezers have been used to characterize individual organelles of F1C type expressed by UPEC bacteria with respect to such properties. Qualitatively, the force-versus-elongation response was found to be similar to that of other types of helix-like pili expressed by UPEC, i.e., type 1, P, and S, with force-induced elongation in three regions, one of which represents the important uncoiling mechanism of the helix-like quaternary structure. Quantitatively, the steady-state uncoiling force was assessed as 26.4 ±1.4 pN, which is similar to those of other pili (which range from 21 pN for S(I) to 30 pN for type 1). The corner velocity for dynamic response (1,400 nm/s) was found to be larger than those of the other pili (400-700 nm/s for S and P pili, and 6 nm/s for type 1). The kinetics were found to be faster, with a thermal opening rate of 17 Hz, a few times higher than S and P pili, and three orders of magnitude higher than type 1. These data suggest that F1C pili are, like P and S pili, evolutionarily selected to primarily withstand the conditions expressed in the upper urinary tract.

Dynamic Modulation of Fimbrial Extension and FimH-Mannose Binding Force on Live Bacteria Under pH Changes: A Molecular Atomic Force Microscopy Analysis

“…21,22,43 The dependence of CFA/I (colonization factor antigen I) pili rupture force on pulling rate was observed for pulling rate larger than a critical value (1.4 µm/s) referred to as the corner velocity. 21 Our results are consistent with pulling rate dependentrupture force and elongation as reported for CFA/P/I pili 19,22,44 , and they additionally evidence a strong influence of solution pH on the extent of fimbrial unwinding, as schematically illustrated in Figure S5 and Figure S6.…”

“…It was reported that both pili are highly flexible and they may be viewed as dynamic structures with spring-like properties. 5,[16][17][18] Indeed, when bacteria were subjected to hydrodynamic constrains, these structures maintain bacterial attachment to host cells or surfaces by reducing the impact of flushes and associated mechanical stress 5,19 following an unwinding of the pointed out that the length of P-pili and type 1 fimbriae could increase by a factor 5 following such unwinding process under high shear stress conditions. [20][21][22] The forced unraveling of type 1 fimbriae is reversible, with helical rewinding taking place for shear forces of magnitude ~ 60 pN.…”

Biomechanical and Structural Features of CS2 Fimbriae of Enterotoxigenic Escherichia coli

“…We observed that the force response of multiple fimbriae was additive, as seen for other helix-like fimbriae (39). Fig.…”

“…ETEC fimbriae such as CS2, CFA/I, and CS20 require <15 pN unwinding force, despite differences in their assembly mechanism (see Table S1 and our previous work (24,26)); UPEC and meningitis-associated strains of E. coli express fimbriae requiring 21-30 pN of unwinding force (33,39,42); however, Type 3 fimbriae expressed by K. pneumonia in the respiratory tract require 66 pN of unwinding force (43). One should also note that the T4 fimbriae expressed by Streptococcus pneumonia, which also colonize the respiratory tract, are significantly stiffer than UPEC-and ETEC-expressed fimbriae (45).…”

“…This particular transition point is denoted the corner velocity, _ L Ã (28). Thus, for velocities below the corner velocity, fimbria extension occurs independent of speed and the experiment is performed under steady-state conditions, whereas for velocities above the corner velocity ( _ L Ã < _ L) fimbriae enter a dynamic response region (39).…”