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Fällman, Erik
Publications (10 of 19) Show all publications
Castelain, M., Sjöström, A. E., Fällman, E., Uhlin, B. E. & Andersson, M. (2010). Unfolding and refolding properties of S pili on extraintestinal pathogenic Escherichia coli. European Biophysics Journal, 39(8), 1105-1115
Open this publication in new window or tab >>Unfolding and refolding properties of S pili on extraintestinal pathogenic Escherichia coli
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2010 (English)In: European Biophysics Journal, ISSN 0175-7571, E-ISSN 1432-1017, Vol. 39, no 8, p. 1105-1115Article in journal (Refereed) Published
Abstract [en]

S pili are members of the chaperone-usher-pathway-assembled pili family that are predominantly associated with neonatal meningitis (S(II)) and believed to play a role in ascending urinary tract infections (S(I)). We used force-measuring optical tweezers to characterize the intrinsic biomechanical properties and kinetics of S(II) and S(I) pili. Under steady-state conditions, a sequential unfolding of the layers in the helix-like rod occurred at somewhat different forces, 26 pN for S(II) pili and 21 pN for S(I) pili, and there was an apparent difference in the kinetics, 1.3 and 8.8 Hz. Tests with bacteria defective in a newly recognized sfa gene (sfaX (II)) indicated that absence of the sfaX (II) gene weakens the interactions of the fimbrium slightly and decreases the kinetics. Data of S(I) are compared with those of previously assessed pili primary associated with urinary tract infections, the P and type 1 pili. S pili have weaker layer-to-layer bonds than both P and type 1 pili, 21, 28 and 30 pN, respectively. In addition, the S pili kinetics are ~10 times faster than the kinetics of P pili and ~550 times faster than the kinetics of type 1 pili. Our results also show that the biomechanical properties of pili expressed ectopically from a plasmid in a laboratory strain (HB101) and pili expressed from the chromosome of a clinical isolate (IHE3034) are identical. Moreover, we demonstrate that it is possible to distinguish, by analyzing force-extension data, the different types of pili expressed by an individual cell of a clinical bacterial isolate.

Keywords
Fimbriae, uropathogenic escherichia coli, bond breaking, unfolding, optical tweezers
National Category
Cell and Molecular Biology
Identifiers
urn:nbn:se:umu:diva-32913 (URN)10.1007/s00249-009-0552-8 (DOI)000279194500001 ()19885656 (PubMedID)
Available from: 2010-03-30 Created: 2010-03-30 Last updated: 2018-06-08Bibliographically approved
Andersson, M., Axner, O., Almqvist, F., Uhlin, B. E. & Fällman, E. (2008). Physical Properties of Biopolymers Assessed by Optical Tweezers: Analysis of folding and refolding of bacterial pili. ChemPhysChem, 9(2), 221-235
Open this publication in new window or tab >>Physical Properties of Biopolymers Assessed by Optical Tweezers: Analysis of folding and refolding of bacterial pili
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2008 (English)In: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 9, no 2, p. 221-235Article in journal (Refereed) Published
Abstract [en]

Bacterial adhesion to surfaces mediated by specific adhesion organelles that promote infections, as exemplified by the pili of uropathogenic E. coli, is studied mostly at the level of cell-cell interactions and thereby reflects the averaged behavior of multiple pili. The role of pilus rod structure has therefore only been estimated from the outcome of experiments involving large numbers of organelles at the same time. It has, however, lately become clear that the biomechanical behavior of the pilus shafts play an important, albeit hitherto rather unrecognized, role in the adhesion process. For example, it has been observed that shafts from two different strains, even though they are similar in structure, result in large differences in the ability of the bacteria to adhere to their host tissue. However, in order to identify all properties of pilus structures that are of importance in the adhesion process, the biomechanical properties of pili must be assessed at the single-molecule level. Due to the low range of forces of these structures, until recently it was not possible to obtain such information. However, with the development of force-measuring optical tweezers (FMOT) with force resolution in the low piconewton range, it has lately become possible to assess forces mediated by individual pili on single living bacteria in real time. FMOT allows for a more or less detailed mapping of the biomechanical properties of individual pilus shafts, in particular those that are associated with their elongation and contraction under stress. This Mi- nireview presents the FMOT technique, the biological model system, and results from assessment of the biomechanical properties of bacterial pili. The information retrieved is also compared with that obtained by atomic force microscopy.

Keywords
bacterial adhesion, force spectroscopy, mechanical properties, optical tweezers´, single-molecule studies
Identifiers
urn:nbn:se:umu:diva-17336 (URN)doi:10.1002/cphc.200700389 (DOI)
Available from: 2008-01-25 Created: 2008-01-25 Last updated: 2018-06-09Bibliographically approved
Andersson, M. & Fällman, E. (2007). Characterization of S pili — investigation of their mechanical properties.
Open this publication in new window or tab >>Characterization of S pili — investigation of their mechanical properties
2007 (English)Manuscript (preprint) (Other (popular science, discussion, etc.))
Identifiers
urn:nbn:se:umu:diva-2752 (URN)
Available from: 2007-11-08 Created: 2007-11-08 Last updated: 2018-06-09Bibliographically approved
Klein, M., Andersson, M., Axner, O. & Fällman, E. (2007). Dual-trap technique for reduction of low-frequency noise in force measuring optical tweezers. Applied Optics, 46(3), 405-412
Open this publication in new window or tab >>Dual-trap technique for reduction of low-frequency noise in force measuring optical tweezers
2007 (English)In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 46, no 3, p. 405-412Article in journal (Refereed) Published
Abstract [en]

High-resolution long-time force measurements by optical tweezers are often limited by low- frequency (1/f) noise. A dual-trap technique is presented that can reduce such noise in the force signal. It incorporates a second trap (a reference trap) that probes the noise in the system and it is based upon the assumption that the low-frequency parts of the noise from the two traps are correlated. A subtraction of the low-frequency signal from the reference trap from the signal from the force measuring trap will therefore yield a net signal that is significantly less influenced by noise. It is shown that this dual-trap technique can reduce the noise in the force signal up to 60% depending on detection bandwidth.

Identifiers
urn:nbn:se:umu:diva-2748 (URN)10.1364/AO.46.000405 (DOI)
Available from: 2007-11-08 Created: 2007-11-08 Last updated: 2018-06-09Bibliographically approved
Klein, M., Andersson, M., Axner, O. & Fällman, E. (2007). Mechanical Noise Elimination in Optical Tweezers Force Measurements. Applied Optics, 46, 405-412
Open this publication in new window or tab >>Mechanical Noise Elimination in Optical Tweezers Force Measurements
2007 (English)In: Applied Optics, Vol. 46, p. 405-412Article in journal (Refereed) Published
Identifiers
urn:nbn:se:umu:diva-10702 (URN)
Available from: 2007-03-02 Created: 2007-03-02 Last updated: 2018-06-09Bibliographically approved
Åberg, V., Fällman, E., Axner, O., Uhlin, B. E., Hultgren, S. J. & Almqvist, F. (2007). Pilicides regulate pili expression in E. coli without affecting the functional properties of the pilus rod. Molecular BioSystems, 3, 214-218
Open this publication in new window or tab >>Pilicides regulate pili expression in E. coli without affecting the functional properties of the pilus rod
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2007 (English)In: Molecular BioSystems, ISSN 1742-206X, Vol. 3, p. 214-218Article in journal (Refereed) Published
Abstract [en]

The infectious ability of uropathogenic Escherichia coli relies on adhesive fibers, termed pili or fimbriae, that are expressed on the bacterial surface. Pili are multi-protein structures that are formed via a highly preserved assembly and secretion system called the chaperone-usher pathway. We have earlier reported that small synthetic compounds, referred to as pilicides, disrupt both type 1 and P pilus biogenesis in E. coli. In this study, we show that the pilicides do not affect the structure, dynamics or function of the pilus rod. This was demonstrated by first suppressing the expression of P pili in E. coli by pilicide treatment and, next, measuring the biophysical properties of the pilus rod. The reduced abundance of pili was assessed with hemagglutination, atomic force microscopy and Western immunoblot analysis. The biodynamic properties of the pili fibers were determined by optical tweezers force measurements on individual pili and were found to be intact. The presented results establish a potential use of pilicides as chemical tools to study important biological processes e.g. adhesion, pilus biogenesis and the role of pili in infections and biofilm formation.

Place, publisher, year, edition, pages
Cambridge: Royal Society of Chemistry, 2007
Identifiers
urn:nbn:se:umu:diva-12792 (URN)10.1039/B613441F (DOI)
Available from: 2007-10-03 Created: 2007-10-03 Last updated: 2018-06-09Bibliographically approved
Andersson, M., Uhlin, B. E. & Fällman, E. (2007). The biomechanical properties of E. coli pili for urinary tract attachment reflect the host environment. Biophysical Journal, 93(9), 3008-3014
Open this publication in new window or tab >>The biomechanical properties of E. coli pili for urinary tract attachment reflect the host environment
2007 (English)In: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 93, no 9, p. 3008-3014Article in journal (Refereed) Published
Abstract [en]

Uropathogenic Escherichia coli express pili that mediate binding to host tissue cells. We demonstrate with in situ force measuring optical tweezers that the ability of P and type 1 pili to elongate by unfolding under exposure to stress is a shared property with some differences. The unfolding force of the quaternary structures under equilibrium conditions is similar, 28 ± 2 and 30 ± 2 pN for P pili and type 1 pili, respectively. However, type 1 pili are found to be more rigid than P pili through their stronger layer-to-layer bonds. It was found that type 1 pili enter a dynamic regime at elongation speeds of 6 nm/s, compared to 400 nm/s for P pili; i.e., it responds faster to an external force. This possibly helps type 1 to withstand the irregular urine flow in the urethra as compared to the more constant urine flow in the upper urinary tract. Also, it was found that type 1 pili refold during retraction at two different levels that possibly could be related to several possible configurations. Our findings highlight functions that are believed to be of importance for the bacterial ability to sustain a basic antimicrobial mechanism of the host and for bacterial colonization.

Keywords
Bacterial Adhesion/*physiology, Biomechanics, Escherichia coli/*physiology, Fimbriae; Bacterial/*chemistry/*physiology, Humans, Microscopy; Atomic Force, Optical Tweezers, Urinary Tract Infections/microbiology, Urinary Tract Physiology
Identifiers
urn:nbn:se:umu:diva-2750 (URN)10.1529/biophysj.107.110643 (DOI)
Available from: 2007-11-08 Created: 2007-11-08 Last updated: 2018-06-09Bibliographically approved
Andersson, M., Fällman, E., Uhlin, B. E. & Axner, O. (2006). A sticky chain model of the elongation and unfolding of escherichia coli P pili under stress. Biophysical Journal, 90(5), 1521-1534
Open this publication in new window or tab >>A sticky chain model of the elongation and unfolding of escherichia coli P pili under stress
2006 (English)In: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 90, no 5, p. 1521-1534Article in journal (Refereed) Published
Abstract [en]

A model of the elongation of P pili expressed by uropathogenic Escherichia coli exposed to stress is presented. The model is based upon the sticky chain concept, which is based upon Hooke’s law for elongation of the layer-to-layer and head-to-tail bonds between neighboring units in the PapA rod and a kinetic description of the opening and closing of bonds, described by rate equations and an energy landscape model. It provides an accurate description of the elongation behavior of P pili under stress and supports a hypothesis that the PapA rod shows all three basic stereotypes of elongation/unfolding: elongation of bonds in parallel, the zipper mode of unfolding, and elongation and unfolding of bonds in series. The two first elongation regions are dominated by a cooperative bond opening, in which each bond is influenced by its neighbor, whereas the third region can be described by individual bond opening, in which the bonds open and close randomly. A methodology for a swift extraction of model parameters from force-versus-elongation measurements performed under equilibrium conditions is derived. Entities such as the free energy, the stiffness, the elastic elongation, the opening length of the various bonds, and the number of PapA units in the rod are determined.

Identifiers
urn:nbn:se:umu:diva-2744 (URN)10.1529/biophysj.105.074674 (DOI)
Available from: 2007-11-08 Created: 2007-11-08 Last updated: 2018-06-09Bibliographically approved
Andersson, M., Axner, O., Uhlin, B. E. & Fällman, E. (2006). Characterization of the mechanical properties of fimbrial structures by optical tweezers. In: Proceedings of the VIII. Annual Linz Winter Workshop (pp. 19-22).
Open this publication in new window or tab >>Characterization of the mechanical properties of fimbrial structures by optical tweezers
2006 (English)In: Proceedings of the VIII. Annual Linz Winter Workshop, 2006, p. 19-22Conference paper, Published paper (Refereed)
Identifiers
urn:nbn:se:umu:diva-10733 (URN)3-85499-163-0 (ISBN)
Available from: 2007-10-03 Created: 2007-10-03 Last updated: 2018-06-09Bibliographically approved
Andersson, M., Fällman, E., Uhlin, B. E. & Axner, O. (2006). Dynamic Force Spectroscopy of E. coli P Pili. Biophysical Journal, 91(7), 2717-2725
Open this publication in new window or tab >>Dynamic Force Spectroscopy of E. coli P Pili
2006 (English)In: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 91, no 7, p. 2717-2725Article in journal (Refereed) Published
Abstract [en]

Surface organelles (so-called pili) expressed on the bacterial membrane mediate the adhesion of Escherichia coli causing urinary tract infection. These pili possess some extraordinary elongation properties that are assumed to allow a close bacterium-to-host contact even in the presence of shear forces caused by urine flow. The elongation properties of P pili have therefore been assessed for low elongation speeds (steady-state conditions). This work reports on the behavior of P pili probed by dynamic force spectroscopy. A kinetic model for the unfolding of a helixlike chain structure is derived and verified. It is shown that the unfolding of the quaternary structure of the PapA rod takes place at a constant force that is almost independent of elongation speed for slow elongations (up to ~0.4 μm/s), whereas it shows a dynamic response with a logarithmic dependence for fast elongations. The results provide information about the energy landscape and reaction rates. The bond length and thermal bond opening and closure rates for the layer-to-layer bond have been assessed to ~0.76 nm, ~0.8 Hz, and ~8 GHz, respectively. The results also support a previously constructed sticky-chain model for elongation of the PapA rod that until now had been experimentally verified only under steady-state conditions.

Identifiers
urn:nbn:se:umu:diva-2745 (URN)10.1529/biophysj.106.087429 (DOI)
Available from: 2007-11-08 Created: 2007-11-08 Last updated: 2018-06-09Bibliographically approved
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