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The shaft of the type 1 fimbriae regulates an externalforce to match the FimH catch bond
Umeå University, Faculty of Science and Technology, Department of Physics. Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR).
Umeå University, Faculty of Science and Technology, Department of Physics. Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR).
Umeå University, Faculty of Science and Technology, Department of Physics. Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR).
Umeå University, Faculty of Science and Technology, Department of Physics. Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR). (The Biophysics and Biophotonics group)
2013 (English)In: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 104, no 10, 2137-2148 p.Article in journal (Refereed) Published
Abstract [en]

Type 1 fimbriae mediate adhesion of uropathogenic Escherichia coli to host cells. It has been hypothesized that due to their ability to uncoil under exposure to force, fimbriae can reduce fluid shear stress on the adhesin-receptor interaction by which the bacterium adheres to the surface. In this work, we develop a model that describes how the force on the adhesin-receptor interaction of a type 1 fimbria varies as a bacterium is affected by a time-dependent fluid flow mimicking in vivo conditions. The model combines in vivo hydrodynamic conditions with previously assessed biomechanical properties of the fimbriae. Numerical methods are used to solve for the motion and adhesion force under the presence of time-dependent fluid profiles. It is found that a bacterium tethered with a type 1 pilus will experience significantly reduced shear stress for moderate to high flow velocities and that the maximum stress the adhesin will experience is limited to ∼120 pN, which is sufficient to activate the conformational change of the FimH adhesin into its stronger state but also lower than the force required for breaking it under rapid loading. Our model thus supports the assumption that the type 1 fimbria shaft and the FimH adhesin-receptor interaction are optimized to each other, and that they give piliated bacteria significant advantages in rapidly changing fluidic environments.

Place, publisher, year, edition, pages
2013. Vol. 104, no 10, 2137-2148 p.
Keyword [en]
type 1, E coli, pili, optical tweezers, FimH
National Category
Biophysics Physical Sciences
Research subject
URN: urn:nbn:se:umu:diva-64463DOI: 10.1016/j.bpj.2013.03.059ISI: 000319318400008PubMedID: 23708354OAI: diva2:601389
Available from: 2013-01-29 Created: 2013-01-29 Last updated: 2016-04-28Bibliographically approved
In thesis
1. The mechanics of adhesion polymers and their role in bacterial attachment
Open this publication in new window or tab >>The mechanics of adhesion polymers and their role in bacterial attachment
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Bacterial resistance to antibiotics is increasing at a high rate in both developing and developed countries. To circumvent the problem of drug-resistant bacterial pathogens, we need to develop new effective methods, substances, and materials that can disarm and prevent them from causing infections. However, to do this we first need to find new possible targets in bacteria to approach and novel strategies to apply.Escherichia coli (E. coli) bacteria is a normal member of the intestinal microflora of humans and mammals, but frequently cause diverse intestinal and external diseases by means of virulence factors, which leads to hundreds of million sick people each year with a high mortality rate. An E. coli bacterial infection starts with adhesion to a host cell using cell surface expressed adhesion polymers, called adhesion pili. Depending on the local environment different types of pili are expressed by the bacteria. For example, bacteria found in the gastrointestinal tract commonly express different pili in comparison to those found in the urinary tract and respiratory tract. These pili, which are vital for bacterial adhesion, thereby serve as a new possible approach in the fight against bacterial infections by targeting and disabling these structures using novel chemicals. However, in order to develop such chemicals, better understanding of these pili is needed.Optical tweezers (OT) can measure and apply forces up to a few hundred pN with sub-pN force resolution and have shown to be an excellent tool for investigating mechanical properties of adhesion pili. It has been found that pili expressed by E. coli have a unique and complex force-extension response that is assumed to be important for the ability of bacteria to initiate and maintain attachment to the host cells. However, their mechanical functions and the advantage of specific mechanical functions, especially in the initial attachment process, have not yet been fully understood.In this work, a detailed description of the pili mechanics and their role during cell adhesion is presented. By using results from optical tweezers force spectroscopy experiments in combination with physical modeling and numerical simulations, we investigated how pili can act as “shock absorbers” through uncoiling and thereby lower the fluid force acting on a bacterium. Our result demonstrate that the dynamic uncoiling capability of the helical part of the adhesion pili modulate the force to fit the optimal lifetime of its adhesin (the protein that binds to the receptor on the host cell), ensuring a high survival probability of the bond.iiiSince the attachment process is in proximity of a surface we also investigated the influence of tether properties and the importance of different surface corrections and additional force components to the Stokes drag force during simulations. The investigation showed that the surface corrections to the Stokes drag force and the Basset force cannot be neglected when simulating survival probability of a bond, since that can overestimate the probability by more than an order of magnitude.Finally, a theoretical and experimental framework for two separate methods was developed. The first method can detect the presence of pili on single cells using optical tweezers. We verified the method using silica microspheres coated with a polymer brush and E. coli bacteria expressing; no pili, P pili, and type 1 pili, respectively. The second method was based on digital holography microscopy. Using the diffraction of semi-transparent object such as red blood cells, we showed that this method can reconstruct the axial position and detect morphological changes of cells.

Place, publisher, year, edition, pages
Umeå: Umeå universitet, 2015. 65 p.
Pili, optical tweezers, bacterial adhesion, fimbriae, uncoiling
National Category
Other Physics Topics Biophysics
urn:nbn:se:umu:diva-109524 (URN)978-91-7601-331-1 (ISBN)
Public defence
2015-10-23, Naturvetarhuset, N420, Umeå universitet, Umeå, 13:00 (English)
Available from: 2015-10-02 Created: 2015-09-30 Last updated: 2015-10-02Bibliographically approved

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Zakrisson, JohanWiklund, KristerAxner, OveAndersson, Magnus
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