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  • 1.
    Andersson, Magnus
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Physics.
    Almqvist, Fredrik
    Umeå University, Faculty of Science and Technology, Chemistry.
    Uhlin, Bernt Eric
    Umeå University, Faculty of Medicine, Molecular Biology (Faculty of Medicine).
    Fällman, Erik
    Umeå University, Faculty of Science and Technology, Physics.
    Physical Properties of Biopolymers Assessed by Optical Tweezers: Analysis of folding and refolding of bacterial pili2008In: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 9, no 2, p. 221-235Article in journal (Refereed)
    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.

  • 2.
    Andersson, Magnus
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Physics.
    Uhlin, Bernt Eric
    Faculty of Medicine, Molecular Biology (Faculty of Medicine).
    Fällman, Erik
    Umeå University, Faculty of Science and Technology, Physics.
    Characterization of the mechanical properties of fimbrial structures by optical tweezers2006In: Proceedings of the VIII. Annual Linz Winter Workshop, 2006, p. 19-22Conference paper (Refereed)
  • 3.
    Andersson, Magnus
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Physics.
    Uhlin, Bernt Eric
    Umeå University, Faculty of Medicine, Molecular Biology (Faculty of Medicine).
    Fällman, Erik
    Umeå University, Faculty of Science and Technology, Physics.
    Optical tweezers for single molecule force spectroscopy on bacterial adhesion organelles2006In: Proceedings of SPIE vol. 6326: Optical Trapping and Optical Micromanipulation III, 2006, p. 632620-Conference paper (Refereed)
  • 4.
    Andersson, Magnus
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Björnham, Oscar
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Bullitt, Esther
    Department of Physiology and Biophysics, Boston University School of Medicine, 700 Albany St., Boston MA, USA.
    Svantesson, Mats
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Uhlin, Bernt Eric
    Umeå University, Faculty of Medicine, Department of Molecular Biology (Faculty of Medicine). Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR).
    Differentiating pili expressed by enterotoxigenic and uropathogenic escherichia coli with optical tweezersManuscript (preprint) (Other academic)
    Abstract [en]

    Enterotoxigenic Escherichia coli (ETEC) attach to the host epithelium in the intestinal tract via specific adhesion organelles expressed on the cell membrane. We investigate, by force measuring optical tweezers, the intrinsic biomechanical properties and kinetics of the colonization factor I (CFA/I) at a single pilus level. The measurements indicate that CFA/I pili are helix-like structures that can both be unraveled to a linearized polymer by applying a small external force, 7.5 ± 1.5 pN but also regain its helix-like structure when the applied force is reduced. The data confirm that layer-to-layer interactions, that stabilize the helix-like structure, are much weaker than the interactions found in pili expressed by Uropathogenic Escherichia coli (UPEC). It is also found, contrary to previous results assessed from UPEC pili, that the CFA/I undergo in some cases a sudden structural change, a force drop of ~2 pN, when unraveled from the helix-like configuration to an open helical linearized fiber. These data suggest a rotation of the filament about its helical axis, followed by a region in which the force required to extend the pili further increases rapidly. During this final elongation to a super-extended fiber, CFA/I pili do not show any structural transition as seen for UPEC pili. In addition, the CFA/I pili show faster kinetics than UPEC pili that allows for a larger dynamic regime of in vivo shear forces. The unfolding and refolding possibility points toward an organelle that has evolved to allow for dynamic damping of external forces and handling of harsh motion without breaking.

  • 5.
    Andersson, Magnus
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Czerwinski, Fabian
    The Niels Bohr Institute, University of Copenhagen, Denmark.
    Oddershede, L B
    The Niels Bohr Institute, University of Copenhagen, Denmark.
    Optimizing active and passive calibration of optical tweezers2011In: Journal of optics, ISSN 0150-536X, Vol. 13, no 4Article in journal (Refereed)
    Abstract [en]

    To obtain quantitative information from optical trapping experiments it is essential to perform a precise force calibration. Therefore, sources of noise should be pinpointed and eliminated. Fourier analysis is routinely used to calibrate optical trapping assays because it is excellent for pinpointing high frequency noise. In addition, Allan variance analysis is particularly useful for quantifying low frequency noise and for predicting the optimal measurement time. We show how to use Allan variance in combination with Fourier analysis for optimal calibration and noise reduction in optical trapping assays. The methods are applied to passive assays, utilizing the thermal motion of a trapped particle, and to active assays where the bead is harmonically driven. The active method must be applied in assays where, for example, the viscoelastic properties of the medium or the size or shape of the trapped object are unknown. For measurement times shorter than the optimal calibration time the noise is larger in active than in the passive assays. For times equal to or longer than the optimal measurement time, though, the noise on passive and active assays is identical. As an example, we show how to quantify the influence on measurement noise of bead size and chamber geometry in active and passive assays.

  • 6.
    Andersson, Magnus
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Fällman, Erik
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Characterization of S pili — investigation of their mechanical properties2007Manuscript (preprint) (Other (popular science, discussion, etc.))
  • 7.
    Andersson, Magnus
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Fällman, Erik
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Hedman, Håkan
    Umeå University, Faculty of Medicine, Department of Radiation Sciences.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Model System for in Situ Investigation of Binding Strengths of Integrin Mediated Cellular Adhesion2003In: World congress on medical physics and biomedical engineering, 2003Conference paper (Other academic)
  • 8.
    Andersson, Magnus
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Fällman, Erik
    Umeå University, Faculty of Science and Technology, Physics.
    Uhlin, Bernt Eric
    Umeå University, Faculty of Medicine, Molecular Biology (Faculty of Medicine).
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Physics.
    A sticky chain model of the elongation and unfolding of escherichia coli P pili under stress2006In: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 90, no 5, p. 1521-1534Article in journal (Refereed)
    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.

  • 9.
    Andersson, Magnus
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Fällman, Erik
    Umeå University, Faculty of Science and Technology, Physics.
    Uhlin, Bernt Eric
    Umeå University, Faculty of Medicine, Molecular Biology (Faculty of Medicine).
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Physics.
    Dynamic Force Spectroscopy of E. coli P Pili2006In: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 91, no 7, p. 2717-2725Article in journal (Refereed)
    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.

  • 10.
    Andersson, Magnus
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Fällman, Erik
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Uhlin, Bernt Eric
    Umeå University, Faculty of Medicine, Department of Molecular Biology (Faculty of Medicine).
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Force measuring optical tweezers system for long time measurements of P pili stability2006In: Imaging, Manipulation, and Analysis of Biomolecules, Cells, and Tissues IV / [ed] Farkas, DL, Nicolau, DV, Leif, RC, 2006, Vol. 6088, p. 608810-Conference paper (Refereed)
    Abstract [en]

    A force-measuring optical tweezers instrumentation and long time measurements of the elongation and retraction of bacterial fimbriae from Uropathogenic E. coli (UPEC) under strain are presented. The instrumentation is presented in some detail. Special emphasis is given to measures taken to reduce the influence of noise and drifts in the system and from the surrounding, which makes long term force measurements possible. Individual P pili from UPEC bacteria were used as a biological model system for repetitive unfolding and refolding cycles of bacterial fimbriae under equilibrium conditions. P pili have evolved into a three-dimensional helix-like structure, the PapA rod, that can be successively and significantly elongated and/or unfolded when exposed to external forces. The instrumentation is used for characterization of the force-vs.-elongation response of the PapA rod of individual P pili, with emphasis on the long time stability of the forced unfolding and refolding of the helical structure of the PapA rod. The results show that the PapA rod is capable of withstanding extensive strain, leading to a complete unfolding of the helical structure, repetitive times during the life cycle of a bacterium without any noticeable alteration of the mechanical properties of the P pili. This function is believed to be importance for UPEC bacteria in vivo since it provides a close contact to a host cell (which is an initial step of invasion) despite urine cleaning attempts.

  • 11.
    Andersson, Magnus
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Fällman, Erik
    Umeå University, Faculty of Science and Technology, Physics.
    Uhlin, Bernt Eric
    Umeå University, Faculty of Medicine, Molecular Biology (Faculty of Medicine).
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Physics.
    Force measuring optical tweezers system for long time measurements of P pili stability2006In: Proceedings of the SPIE vol. 6088: Imaging, Manipulation, and Analysis of Biomolecules, Cells, and Tissues IV, 2006, p. 608810-Conference paper (Refereed)
  • 12.
    Andersson, Magnus
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Fällman, Erik
    Umeå University, Faculty of Science and Technology, Physics.
    Uhlin, Bernt Eric
    Umeå University, Faculty of Science and Technology, Physics.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Physics.
    Technique for determination of the number of PapA units in an E. coli P pilus2006In: Proceedings of the SPIE vol. 6088: Imaging, Manipulation, and Analysis of Biomolecules, Cells, and Tissues IV, 2006, p. 608814-Conference paper (Refereed)
  • 13.
    Andersson, Magnus
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Svantesson, Mats
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Björnham, Oscar
    Swedish Defence Research Agency (FOI), SE-906 21 Umeå, Sweden.
    Badahdah, Arwa
    Department of Oral Biology, Boston University School of Dental Medicine.
    Uhlin, Bernt Eric
    Umeå University, Faculty of Medicine, Department of Molecular Biology (Faculty of Medicine).
    Bullitt, Esther
    Department of Physiology and Biophysics, Boston University School of Medicine.
    A structural basis for sustained bacterial adhesion: Biomechanical properties of CFA/I Pili2012In: Journal of Molecular Biology, ISSN 0022-2836, E-ISSN 1089-8638, Vol. 415, no 5, p. 918-928Article in journal (Refereed)
    Abstract [en]

    Enterotoxigenic Escherichia coli (ETEC) are a major cause of diarrheal disease worldwide. Adhesion pili (or fimbriae), such as the CFA/I (colonization factor antigen I) organelles that enable ETEC to attach efficiently to the host intestinal tract epithelium, are critical virulence factors for initiation of infection. We characterized at single organelle level the intrinsic biomechanical properties and kinetics of individual CFA/I pili, demonstrating that weak external forces (7.5 pN) are sufficient to unwind the intact helical filament of this prototypical ETEC pilus and that it quickly regains its original structure when the force is removed. While the general relationship between exertion of force and an increase in the filament length for CFA/I pili associated with diarrheal disease is analogous to that of P-pili and type 1 pili, associated with urinary tract and other infections, the biomechanical properties of these different pili differ in key quantitative details. Unique features of CFA/I pili, including the significantly lower force required for unwinding, the higher extension speed at which the pili enter a dynamic range of unwinding, and the appearance of sudden force drops during unwinding can be attributed to morphological features of CFA/I pili including weak layer-to-layer interactions between subunits on adjacent turns of the helix, and the approximately horizontal orientation of pilin subunits with respect to the filament axis. Our results indicate that ETEC CFA/I pili are flexible organelles optimized to withstand harsh motion without breaking, resulting in continued attachment to the intestinal epithelium by the pathogenic bacteria that express these pili.

  • 14.
    Andersson, Magnus
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Uhlin, Bernt Eric
    Umeå University, Faculty of Medicine, Molecular Biology (Faculty of Medicine).
    Fällman, Erik
    Umeå University, Faculty of Science and Technology, Physics.
    The biomechanical properties of E. coli pili for urinary tract attachment reflect the host environment2007In: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 93, no 9, p. 3008-3014Article in journal (Refereed)
    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.

  • 15.
    Axner, Ove
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR).
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Department of Physics. Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR).
    Björnham, Oscar
    Umeå University, Faculty of Science and Technology, Department of Physics. Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR).
    Castelain, Mickaël
    Umeå University, Faculty of Science and Technology, Department of Physics. Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR).
    Klinth, Jeanna
    Umeå University, Faculty of Science and Technology, Department of Physics. Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR).
    Koutris, Efstratios
    Umeå University, Faculty of Science and Technology, Department of Physics. Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR).
    Schedin, Staffan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics. Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR).
    Assessing bacterial adhesion on an individual adhesin and single pili level using optical tweezers 2011In: Bacterial adhesion: chemistry, biology and physics / [ed] D. Line and A. Goldman, Berlin: Springer Berlin/Heidelberg, 2011, p. 301-313Chapter in book (Refereed)
    Abstract [en]

    Optical tweezers (OT) are a technique that, by focused laser light, can both manipulate micrometer sized objects and measure minute forces (in the pN range) in biological systems. The technique is therefore suitable for assessment of bacterial adhesion on an individual adhesin-receptor and single attachment organelle (pili) level. This chapter summarizes the use of OT for assessment of adhesion mechanisms of both non-piliated and piliated bacteria. The latter include the important helix-like pili expressed by uropathogenic Escherichia coli (UPEC), which have shown to have unique and intricate biomechanical properties. It is conjectured that the large flexibility of this type of pili allows for a redistribution of an external shear force among several pili, thereby extending the adhesion lifetime of bacteria. Systems with helix-like adhesion organelles may therefore act as dynamic biomechanical machineries, enhancing the ability of bacteria to withstand high shear forces originating from rinsing flows such as in the urinary tract. This implies that pili constitute an important virulence factor and a possible target for future anti-microbial drugs.

  • 16.
    Axner, Ove
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Björnham, Oscar
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Castelain, Mickael
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Koutris, Efstratios
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Schedin, Staffan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Fällman, Erik
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Unraveling the secrets of bacterial adhesion organelles using single-molecule force spectroscopy2010In: Single molecule spectroscopy in chemistry, physics and biology: Nobel symposium / [ed] Gräslund, Astrid, Rigler, Rudolf & Widengren, Jerker, Springer, 2010, p. 337-362Conference paper (Refereed)
    Abstract [en]

    Many types of bacterium express micrometer-long attachment organelles (so-called pili) whose role is to mediate adhesion to host tissue. Until recently, little was known about their function in the adhesion process. Force-measuring optical tweezers (FMOT) have since then been used to unravel the biomechanical properties of various types of pili, primarily those from uropathogenic E. coli, in particular their force-vs.-elongation response, but lately also some properties of the adhesin situated at the distal end of the pilus. This knowledge provides an understanding of how piliated bacteria can sustain external shear forces caused by rinsing processes, e.g., urine flow. It has been found that many types of pilus exhibit unique and complex force-vs.-elongation responses. It has been conjectured that their dissimilar properties impose significant differences in their ability to sustain external forces and that different types of pilus therefore have dissimilar predisposition to withstand different types of rinsing conditions. An understanding of these properties is of high importance since it can serve as a basis for finding new means to combat bacterial adhesion, including that caused by antibiotic-resistance bacteria. This work presents a review of the current status of the assessment of biophysical properties of individual pili on single bacteria exposed to strain/stress, primarily by the FMOT technique. It also addresses, for the first time, how the elongation and retraction properties of the rod couple to the adhesive properties of the tip adhesin.

  • 17.
    Axner, Ove
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Björnham, Oscar
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Castelain, Mickaël
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Koutris, Efstratios
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Schedin, Staffan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Fällman, Erik
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Unraveling the secrets of bacterial adhesion organelles using single molecule force spectroscopy2010In: Springer series in chemical physics: single molecule spectroscopy in chemistry, physics and biology, Springer Verlag , 2010, 96, p. 337-362Chapter in book (Other academic)
    Abstract [en]

    Many types of bacterium express micrometer-long attachment organelles (so called pili) whose role is to mediate adhesion to host tissue. Until recently, little was known about their function in the adhesion process. Forcemeasuring  ptical tweezers (FMOT) have since then been used to unravel the  iomechanical properties of various types of pili, primarily those from uropathogenic E. coli, in particular their force-vs.-elongation response, but lately also some properties of the adhesin situated and the distal end of the pilus. This knowledge provides an understanding of how piliated bacteria can sustain external shear forces caused by rinsing processes, e.g. urine flow. It has been found that anytypes of pilus exhibit unique and complex force-vs.-elongation responses. It has been conjectured that their dissimilar properties impose significant differences in their ability to sustain external forces and that different types of pilus therefore have dissimilar predisposition to withstand different types of rinsing conditions. An understanding of these properties is of high importance since it can serve as a basis for finding new means to combat bacterial adhesion, including that caused by antibiotic-resistance bacteria. This work presents a review of the current status of the assessment of biophysical properties of individual pili on single bacteria exposed to strain/stress, primarily by the FMOT technique. It also addresses, for the first time, how the elongation and retraction properties of the rod couple to the adhesive properties of the tip adhesin.

  • 18. Barbercheck Epler, Chelsea R.
    et al.
    Bullitt, Esther
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Bacterial adhesion pili2018In: Membrane protein complexes: structure and function / [ed] J. Robin Harris, Egbert Boekema, Springer Publishing Company, 2018, , p. 18p. 1-18Chapter in book (Refereed)
    Abstract [en]

    Escherichia coli bacterial cells produce multiple types of adhesion pili that mediate cell-cell and cell-host attachments. These pili (also called 'fimbriae') are large biopolymers that are comprised of subunits assembled via a sophisticated micro-machinery into helix-like structures that are anchored in the bacterial outer membrane. They are commonly essential for initiation of disease and thus provide a potential target for antibacterial prevention and treatment. To develop new therapeutics for disease prevention and treatment we need to understand the molecular mechanisms and the direct role of adhesion pili during pathogenesis. These helix-like pilus structures possess fascinating and unique biomechanical properties that have been thoroughly investigated using high-resolution imaging techniques, force spectroscopy and fluid flow chambers. In this chapter, we first discuss the structure of pili and the micro-machinery responsible for the assembly process. Thereafter, we present methods for measurement of the biomechanics of adhesion pili, including optical tweezers. Data demonstrate unique biomechanical properties of pili that allow bacteria to sustain binding during in vivo fluid shear forces. We thereafter summarize the current biomechanical findings related to adhesion pili and show that pili biomechanical properties are niche-specific. That is, the data suggest that there is an organ-specific adaptation of pili that facilitates infection of the bacteria's target tissue. Thus, pilus biophysical properties are an important part of Escherichia coli pathogenesis, allowing bacteria to overcome hydrodynamic challenges in diverse environments.

  • 19.
    Björnham, Oscar
    et al.
    Swedish Defence Research Agency (FOI), Umeå, Sweden.
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Department of Physics. Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR).
    Theory for nonlinear dynamic force spectroscopy2017In: European Biophysics Journal, ISSN 0175-7571, E-ISSN 1432-1017, Vol. 46, no 3, p. 225-233Article in journal (Refereed)
    Abstract [en]

    Dynamic force spectroscopy (DFS) is an experimental technique that is commonly used to assess information on the strength, energy landscape, and lifetime of noncovalent bio-molecular interactions. DFS traditionally requires an applied force that increases linearly with time so that the bio-complex under investigation is exposed to a constant loading rate. However, tethers or polymers can modulate the applied force in a nonlinear manner. For example, bacterial adhesion pili and polymers with worm-like chain properties are structures that show nonlinear force responses. In these situations, the theory for traditional DFS cannot be readily applied. In this work, we expand the theory for DFS to also include nonlinear external forces while still maintaining compatibility with the linear DFS theory. To validate the theory, we modeled a bio- complex expressed on a stiff, an elastic, and a worm-like chain polymer, using Monte Carlo methods, and assessed the corresponding rupture force spectra. It was found that the nonlinear DFS (NLDFS) theory correctly predicted the numerical results. We also present a protocol suggesting an experimental approach and analysis method of the data to estimate the bond length and the thermal off-rate.

  • 20.
    Björnham, Oscar
    et al.
    Umeå University, Faculty of Science and Technology, Applied Physics and Electronics.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Physics.
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Physics.
    Modeling of the elongation and retraction of Escherichia coli P pili under strain by Monte Carlo simulations2008In: European Biophysics Journal, ISSN 0175-7571, E-ISSN 1432-1017, Vol. 37, no 4, p. 381-391Article in journal (Refereed)
    Abstract [en]

    P pili are fimbrial adhesion organelles expressed by uropathogenic Escherichia coli in the upper urinary tract. They constitute a stiff helix-like polymer consisting of a number of subunits joined by head-to-tail bonds. The elongation and retraction properties of individual P pili exposed to strain have been modeled by Monte Carlo (MC) simulations. The simulation model is based upon a three-state energy landscape that deforms under an applied force. Bond opening and closure are modeled by Bells theory while the elongation of the linearized part of the pilus is described by a worm-like chain model. The simulations are compared with measurements made by force measuring optical tweezers. It was found that the simulations can reproduce pili elongation as well as retraction, under both equilibrium and dynamic conditions, including entropic effects. It is shown that the simulations allow for an assessment of various model parameters, e.g. the unfolding force, energy barrier heights, and various distances in the energy landscape, including their stochastic spread that analytical models are unable to do. The results demonstrate that MC simulations are useful to model elongation and retraction properties of P pili, and therefore presumably also other types of pili, exposed to strain and/or stress. MC simulations are particularly suited for description of helix-like pili since these have an intricate self-regulating mechanical elongation behavior that makes analytical descriptions non-trivial when dynamic processes are studied, or if additional interactions in the rod or the behavior of the adhesion tip needs to be modeled.

  • 21.
    Björnham, Oscar
    et al.
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Nilsson, Håkan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Schedin, Staffan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Physical properties of the specific PapG–galabiose binding in E. coli P pili-mediated adhesion2009In: European Biophysics Journal, ISSN 0175-7571, E-ISSN 1432-1017, Vol. 38, no 2, p. 245-254Article in journal (Refereed)
    Abstract [en]

    Detailed analyses of the mechanisms thatmediate binding of the uropathogenic Escherichia coli tohost cells are essential, as attachment is a prerequisite forthe subsequent infection process. We explore, by means offorce measuring optical tweezers, the interaction betweenthe galabiose receptor and the adhesin PapG expressed byP pili on single bacterial cells. Two variants of dynamicforce spectroscopy were applied based on constant andnon-linear loading force. The specific PapG–galabiosebinding showed typical slip-bond behaviour in the forceinterval (30–100 pN) set by the pilus intrinsic biomechanicalproperties. Moreover, it was found that the bondhas a thermodynamic off-rate and a bond length of2.6×10-3 s-1 and 5.0 Å , respectively. Consequently, thePapG–galabiose complex is significantly stronger thanthe internal bonds in the P pilus structure that stabilizes thehelical chain-like macromolecule. This finding suggeststhat the specific binding is strong enough to enable the Ppili rod to unfold when subjected to strong shear forces inthe urinary tract. The unfolding process of the P pili rodpromotes the formation of strong multipili interaction,which is important for the bacterium to maintain attachmentto the host cells.

  • 22.
    Björnhamn, Oscar
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Fällman, Erik
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Monte carlo simulation of the unfolding and refolding mechanics of P pili2007In: Trends in Optical Micromanipulation, 2007Conference paper (Other academic)
  • 23.
    Castelain, Mickael
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Koutris, Efstratios
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Helixlike pili is a prerequisite of uropathogenic E. coli to adhere to host and withstand urine flow2009In: European Biophysics Journal, ISSN 0175-7571, E-ISSN 1432-1017, Vol. 38, p. S111-Article in journal (Other academic)
  • 24.
    Castelain, Mickaël
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Ehlers, Sarah
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Klinth, Jeanna
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Lindberg, Stina
    Umeå University, Faculty of Medicine, Department of Molecular Biology (Faculty of Medicine).
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Uhlin, Bernt Eric
    Umeå University, Faculty of Medicine, Department of Molecular Biology (Faculty of Medicine).
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Fast uncoiling kinetics of F1C pili expressed by uropathogenic Escherichia coli are revealed on a single pilus level using force-measuring optical tweezers2011In: European Biophysics Journal, ISSN 0175-7571, E-ISSN 1432-1017, Vol. 40, no 3, p. 305-316Article in journal (Refereed)
    Abstract [en]

    Uropathogenic Escherichia coli (UPEC) expressvarious kinds of organelles, so-called pili or fimbriae, thatmediate adhesion to host tissue in the urinary tract throughspecific receptor-adhesin interactions. The biomechanicalproperties of these pili have been considered important forthe ability of bacteria to withstand shear forces from rinsingurine flows. Force-measuring optical tweezers have beenused to characterize individual organelles of F1C typeexpressed by UPEC bacteria with respect to such properties.Qualitatively, the force-versus-elongation response wasfound to be similar to that of other types of helix-like piliexpressed by UPEC, i.e., type 1, P, and S, with force-inducedelongation in three regions, one of which represents theimportant uncoiling mechanism of the helix-like quaternarystructure. Quantitatively, the steady-state uncoiling forcewas assessed as 26.4 ±1.4 pN, which is similar to those ofother pili (which range from 21 pN for SI to 30 pN for type 1).The corner velocity for dynamic response (1,400 nm/s) wasfound to be larger than those of the other pili (400–700 nm/sfor S and P pili, and 6 nm/s for type 1). The kinetics werefound to be faster, with a thermal opening rate of 17 Hz, afew times higher than S and P pili, and three orders ofmagnitude higher than type 1. These data suggest that F1Cpili are, like P and S pili, evolutionarily selected to primarilywithstand the conditions expressed in the upper urinary tract.

  • 25.
    Castelain, Mickaël
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Koutris, Efstratios
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wiklund, Krister
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Björnham, Oscar
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Schedin, Staffan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Characterization of the Biomechanical Properties of T4 Pili Expressed by Streptococcus pneumoniae – A Comparison between Helix-like and Open Coil-like Pili2009In: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 10, no 9-10, p. 1533-1540Article in journal (Refereed)
    Abstract [en]

    Bacterial adhesion organelles, known as fimbria or pili, are expressed by Gram–positive as well as Gram–negative bacteria families. These appendages play a key role in the first steps of the invasion and infection processes, and they therefore provide bacteria with pathogenic abilities. To improve the knowledge of pili-mediated bacterial adhesion to host cells and how these pili behave under the presence of an external force, we first characterize, using force measuring optical tweezers, open coil-like T4 pili expressed by Gram–positive Streptococcus pneumoniae with respect to their biomechanicalproperties. It is shown that their elongation behavior can be well described by the worm-like chain model and that they possess a large degree of flexibility. Their properties are then compared with those of helix-like pili expressed by Gram–negative uropathogenic Escherichia coli (UPEC), which have different pili architecture. The differences suggest that these two types of pili have distinctly dissimilar mechanisms to adhere and sustain external forces. Helix-like pili expressed by UPEC bacteria adhere to host cells by single adhesins located at the distal end of the pili while their helix-like structures act as shock absorbers to dampen the irregularly shear forces induced by urine flow and to increase the cooperativity of the pili ensemble. Open coil-like pili expressed by S. pneumoniae adhere to cells by a multitude of adhesins distributed along the pili. It is hypothesized that these two types of pili represent different strategies of adhering to host cells in the presence of external forces. When exposed to significant forces, bacteria expressing helix-like pili remain attached bydistributing the external force among a multitude of pili, whereas bacteria expressing open coil-like pili sustain large forces primarily by their multitude of binding adhesins.

  • 26.
    Castelain, Mickaël
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sjöström, Annika E
    Umeå University, Faculty of Medicine, Department of Molecular Biology (Faculty of Medicine).
    Fällman, Erik
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Uhlin, Bernt Eric
    Umeå University, Faculty of Medicine, Department of Molecular Biology (Faculty of Medicine).
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Unfolding and refolding properties of S pili on extraintestinal pathogenic Escherichia coli2010In: European Biophysics Journal, ISSN 0175-7571, E-ISSN 1432-1017, Vol. 39, no 8, p. 1105-1115Article in journal (Refereed)
    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.

  • 27.
    Dahlberg, Tobias
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Stangner, Tim
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Hanqing, Zhang
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wiklund, Krister
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Lundberg, Petter
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Department of Physics.
    3D printed water-soluble scaffolds for rapid production of PDMS micro-fluidic flow chambers2018In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, no 1, article id 3372Article in journal (Refereed)
    Abstract [en]

    We report a novel method for fabrication of three-dimensional (3D) biocompatible micro-fluidic flow chambers in polydimethylsiloxane (PDMS) by 3D-printing water-soluble polyvinyl alcohol (PVA) filaments as master scaffolds. The scaffolds are first embedded in the PDMS and later residue-free dissolved in water leaving an inscription of the scaffolds in the hardened PDMS. We demonstrate the strength of our method using a regular, cheap 3D printer, and evaluate the inscription process and the channels micro-fluidic properties using image analysis and digital holographic microscopy. Furthermore, we provide a protocol that allows for direct printing on coverslips and we show that flow chambers with a channel cross section down to 40 x 300 μm can be realized within 60 min. These flow channels are perfectly transparent, biocompatible and can be used for microscopic applications without further treatment. Our proposed protocols facilitate an easy, fast and adaptable production of micro-fluidic channel designs that are cost-effective, do not require specialized training and can be used for a variety of cell and bacterial assays. To help readers reproduce our micro-fluidic devices, we provide: full preparation protocols, 3D-printing CAD files for channel scaffolds and our custom-made molding device, 3D printer build-plate leveling instructions, and G-code.

  • 28.
    Enevold, Jenny
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Larsen, Christian
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Zakrisson, Johan
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Edman, Ludvig
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Realizing large-area arrays of semiconducting fullerene nanostructures with direct laser interference patterning2018In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 18, no 1, p. 540-545Article in journal (Refereed)
  • 29.
    Fällman, Erik
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Physics.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Physics.
    Techniques for moveable traps: The influence of aberration in optical tweezers2006In: Proceedings of the SPIE vol. 6088: Imaging, Manipulation, and Analysis of Biomolecules, Cells, and Tissues IV, 2006, p. 60881E-Conference paper (Refereed)
  • 30.
    Fällman, Erik
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Physics.
    Schedin, Staffan
    Umeå University, Faculty of Science and Technology, Applied Physics and Electronics.
    Jass, Jana
    Umeå University, Faculty of Medicine, Molecular Biology.
    Uhlin, Bernt Eric
    Umeå University, Faculty of Medicine, Molecular Biology (Faculty of Medicine).
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Physics.
    Dynamic properties of bacterial pili measured by optical tweezers2004In: Proceedings of SPIE - The International Society for Optical Engineering vol. 5514: Optical Trapping and Optical Micromanipulation, 2004, p. 763-773Conference paper (Refereed)
  • 31.
    Fällman, Erik
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Schedin, Staffan
    Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
    Jass, Jana
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Uhlin, Bernt Eric
    Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR).
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Measurement of Adhesion Forces With Optical Tweezers: System Description And Experimental Verification2003In: World congress on medical physics and biomedical engineering, 2003Conference paper (Other academic)
  • 32.
    Fällman, Erik
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Schedin, Staffan
    Umeå University, Faculty of Science and Technology, Applied Physics and Electronics.
    Jass, Jana
    Umeå University, Faculty of Medicine, Molecular Biology.
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Physics.
    Uhlin, Bernt Eric
    Umeå University, Faculty of Medicine, Molecular Biology (Faculty of Medicine).
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Physics.
    Optical tweezers based force measurement system for quantitating binding interactions: system design and application for the study of bacterial adhesion2004In: Biosensors & bioelectronics, ISSN 0956-5663, E-ISSN 1873-4235, Vol. 19, no 11, p. 1429-1437Article in journal (Refereed)
    Abstract [en]

    An optical force measurement system for quantitating forces in the pN range between micrometer-sized objects has been developed. The system was based upon optical tweezers in combination with a sensitive position detection system and constructed around an inverted microscope. A trapped particle in the focus of the high numerical aperture microscope-objective behaves like an omnidirectional mechanical spring in response to an external force. The particle’s displacement from the equilibrium position is therefore a direct measure of the exerted force. A weak probe laser beam, focused directly below the trapping focus, was used for position detection of the trapped particle (a polystyrene bead). The bead and the condenser focus the light to a distinct spot in the far field, monitored by a position sensitive detector. Various calibration procedures were implemented in order to provide absolute force measurements. The system has been used to measure the binding forces between Escherichia coli bacterial adhesins and galabiose-functionalized beads

  • 33.
    Hanqing, Zhang
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wiklund, Krister
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Department of Physics.
    A fast and robust circle detection method using isosceles triangles sampling2016In: Pattern Recognition, ISSN 0031-3203, E-ISSN 1873-5142, Vol. 54, p. 218-228Article in journal (Refereed)
    Abstract [en]

    Circle detection using randomized sampling has been developed in recent years to reduce computational intensity. However, randomized sampling is sensitive to noise that can lead to reduced accuracy and false-positive candidates. To improve on the robustness of randomized circle detection under noisy conditions this paper presents a new methodology for circle detection based upon randomized isosceles triangles sampling. It is shown that the geometrical property of isosceles triangles provides a robust criterion to find relevant edge pixels which, in turn, offers an efficient means to estimate the centers and radii of circles. For best efficiency, the estimated results given by the sampling from individual connected components of the edge map were analyzed using a simple clustering approach. To further improve on the accuracy we applied a two-step refinement process using chords and linear error compensation with gradient information of the edge pixels. Extensive experiments using both synthetic and real images have been performed. The results are compared to leading state-of-the-art algorithms and it is shown that the proposed methodology has a number of advantages: it is efficient in finding circles with a low number of iterations, it has high rejection rate of false-positive circle candidates, and it has high robustness against noise. All this makes it adaptive and useful in many vision applications.

  • 34.
    Jonsson, Micael
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Fick, Jerker
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Brodin, Tomas
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Department of Wildlife, Fish, and Environmental Studies, SLU, Umeå, Sweden.
    Klaminder, Jonatan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Piovano, Susanna
    School of Marine Studies, The University of the South Pacific, Suva, Fiji.
    High-speed imaging reveals how antihistamine exposure affects escape behaviours in aquatic insect prey2019In: Science of the Total Environment, ISSN 0048-9697, E-ISSN 1879-1026, Vol. 648, p. 1257-1262Article in journal (Refereed)
    Abstract [en]

    Aquatic systems receive a wide range of pharmaceuticals that may have adverse impacts on aquatic wildlife. Among these pharmaceuticals, antihistamines are commonly found, and these substances have the potential to influence the physiology of aquatic invertebrates. Previous studies have focused on how antihistamines may affect behaviours of aquatic invertebrates, but these studies probably do not capture the full consequences of antihistamine exposure, as traditional recording techniques do not capture important animal movements occurring at the scale of milliseconds, such as prey escape responses. In this study, we investigated if antihistamine exposure can impact escape responses in aquatic insect, by exposing damselfly (Coenagrion hastulatum) larvae to two environmentally relevant concentrations (0.1 and 1 μg L−1) of diphenhydramine. Importantly, we used a high-speed imaging approach that with high-time resolution captures details of escape responses and, thus, potential impacts of diphenhydramine on these behaviours. Our results show overall weak effects of antihistamine exposure on the escape behaviours of damselfly larvae. However, at stage 2 of the C-escape response, we found a significant increase in turning angle, which corresponds to a reduced swimming velocity, indicating a reduced success at evading a predator attack. Thus, we show that low concentrations of an antihistamine may affect behaviours strongly related to fitness of aquatic insect prey – effects would have been overlooked using traditional recording techniques. Hence, to understand the full consequences of pharmaceutical contamination on aquatic wildlife, high-speed imaging should be incorporated into future environmental risk assessments.

  • 35.
    Kamilla, Nørregaard
    et al.
    The Niels Bohr Institute; University of Copenhagen; Copenhagen, Denmark.
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sneppen, Kim
    The Niels Bohr Institute; University of Copenhagen; Copenhagen, Denmark.
    Nielsen, Peter Eigil
    Department of Cellular and Molecular Medicine; Faculty of Health and Sciences; Copenhagen, Denmark.
    Brown, Stanley
    The Niels Bohr Institute; University of Copenhagen; Copenhagen, Denmark.
    Oddershede, Lene
    The Niels Bohr Institute; University of Copenhagen; Copenhagen, Denmark.
    Effect of supercoiling on the λ switch2014In: Bacteriophage, ISSN 2159-7081, Vol. 4, no 1, p. e27517-1-e27517-5Article in journal (Refereed)
    Abstract [en]

    The lysogenic state of the λ switch is exceptionally stable, still, it is capable of responding to DNA-damage and rapidly enter the lytic state. We invented an assay where PNA mediated tethering of a plasmid allowed for single molecule investigations of the effect of supercoiling on the efficiency of the epigenetic λ switch. Compared with non-supercoiled DNA, the presence of supercoils enhances the CI-mediated DNA looping probability and renders the transition between the looped and unlooped states steeper, thus increasing the Hill coefficient. Interestingly, the transition occurs exactly at the CI concentration corresponding to the minimum number of CI molecules capable of maintaining the pRM-repressed state. Based on these results we propose that supercoiling maintains the pRM-repressible state as CI concentration decline during induction and thus prevent autoregulation of cI from interfering with induction.

  • 36.
    Klein, Markus
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Physics.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Physics.
    Fällman, Erik
    Umeå University, Faculty of Science and Technology, Physics.
    Dual-trap technique for reduction of low-frequency noise in force measuring optical tweezers2007In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 46, no 3, p. 405-412Article in journal (Refereed)
    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.

  • 37.
    Klein, Markus
    et al.
    Umeå University, Faculty of Science and Technology, Physics.
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Physics.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Physics.
    Fällman, Erik
    Umeå University, Faculty of Science and Technology, Physics.
    Mechanical Noise Elimination in Optical Tweezers Force Measurements2007In: Applied Optics, Vol. 46, p. 405-412Article in journal (Refereed)
  • 38.
    Lindberg, Ann-Sofie
    et al.
    Winternet.
    Wiklund, Krister
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Malm, Christer
    Umeå University, Faculty of Medicine, Department of Community Medicine and Rehabilitation.
    Firefighters' fit for duty score-model2016Conference paper (Other academic)
  • 39.
    Mortezaei, Narges
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Epler, Chelsea
    Shao, Paul
    Shirdel, Mariam
    Umeå University, Faculty of Medicine, Department of Public Health and Clinical Medicine, Occupational and Environmental Medicine.
    Bhupender, Singh
    Umeå University, Faculty of Science and Technology, Department of Physics.
    McVeigh, Annette
    Uhlin, Bernt Eric
    Umeå University, Faculty of Medicine, Department of Molecular Biology (Faculty of Medicine). Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS).
    Savarino, Stephen
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Bullitt, Esther
    Boston University School of Medicine.
    Structure and function of enterotoxigenic Escherichia coli fimbriae from differing assembly pathways2015In: Molecular Microbiology, ISSN 0950-382X, E-ISSN 1365-2958, Vol. 95, no 1, p. 116-126Article in journal (Refereed)
    Abstract [en]

    Pathogenic enterotoxigenic Escherichia coli (ETEC) are the major bacterial cause of diarrhea in young children in developing countries and in travelers, causing significant mortality in children. Adhesive fimbriae are a prime virulence factor for ETEC, initiating colonization of the small intestinal epithelium. Similar to other Gram-negative bacteria, ETEC express one or more diverse fimbriae, some assembled by the chaperone-usher pathway and others by the alternate chaperone pathway. Here, we elucidate structural and biophysical aspects and adaptations of each fimbrial type to its respective host niche. CS20 fimbriae are compared with colonization factor antigen I (CFA/I) fimbriae, which are two ETEC fimbriae assembled via different pathways, and with P-fimbriae from uropathogenic E.coli. Many fimbriae unwind from their native helical filament to an extended linear conformation under force, thereby sustaining adhesion by reducing load at the point of contact between the bacterium and the target cell. CFA/I fimbriae require the least force to unwind, followed by CS20 fimbriae and then P-fimbriae, which require the highest unwinding force. We conclude from our electron microscopy reconstructions, modeling and force spectroscopy data that the target niche plays a central role in the biophysical properties of fimbriae that are critical for bacterial pathophysiology.

  • 40.
    Mortezaei, Narges
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Epler, Chelsea
    Shao, Paul
    Shirdel, Mariam
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Singh, Bhupender
    Umeå University, Faculty of Science and Technology, Department of Physics. Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS).
    McVeigh, Annette
    Uhlin, Bernt Eric
    Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS).
    Stephen, Savarino
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Bullitt, Esther
    Adhesion Pili from Enterotoxigenic Escherichia coli Share Similar Biophysical Properties Despite Their Different Assembly Pathways2015In: Microscopy and Microanalysis, ISSN 1431-9276, E-ISSN 1435-8115, Vol. 21, p. 915-916Article in journal (Refereed)
  • 41.
    Mortezaei, Narges
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Singh, Bhupender
    Umeå University, Faculty of Medicine, Department of Molecular Biology (Faculty of Medicine). Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS).
    Bullitt, Esther
    Boston University School of Medicine.
    Uhlin, Bernt Eric
    Umeå University, Faculty of Medicine, Department of Molecular Biology (Faculty of Medicine). Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS).
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Department of Physics.
    P-fimbriae in the presence of anti-PapA antibodies: new insight of antibodies action against pathogens2013In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 3, article id 3393Article in journal (Refereed)
    Abstract [en]

    Uropathogenic strains of Escherichia coli establish urinary tract infections by attaching to host epithelial cells using adhesive organelles called fimbriae. Fimbriae are helix-like structures with a remarkable adaptability, offering safeguarding for bacteria exposed to changing fluid forces in the urinary tract. We challenged this property of P-fimbriae by cross-linking their subunits with shaft-specific antibodies and measuring the corresponding force response at a single organelle level. Our data show compromised extension and rewinding of P-fimbriae in the presence of antibodies and reduced fimbrial elasticity, which are important properties of fimbriae contributing to the ability of bacteria to cause urinary tract infections. The reduced elasticity found by cross-linking fimbrial subunits could thus be another assignment for antibodies; in addition to marking bacteria as foreign, antibodies physically compromise fimbrial function. We suggest that our assay and results will be a starting point for further investigations aimed at inhibiting sustained bacterial adhesion by antibodies.

  • 42.
    Mortezaei, Narges
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Singh, Bhupender
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Bullitt, Esther
    Zakrisson, Johan
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Epler, Chelsea
    Wiklund, Krister
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Structural and biophysical comparison of UPEC and ETEC adhesion fimbriae2015In: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 108, no 2, suppl 1, p. 527A-527AArticle in journal (Refereed)
    Abstract [en]

    Adhesion fimbriae (pili) of uropathogenic and enterotoxigenic Escherichia coli (UPEC and ETEC, respectively) facilitate adherence of the bacteria to target cells. Fimbriae are absolutely necessary for colonization and biofilm formation in the initiation of disease. The types of fimbriae expressed on the bacterial surface vary with the preferred environmental niche of the bacterial strain. For example, UPEC that express P-pili are most frequently associated pyelonephritis, an infection in the upper urinary tract, whereas bacteria that express type 1 fimbriae commonly cause cystitis through infection of the lower urinary tract. In contrast, ETEC expressing CFA/I and CS2 pili are associated with diarrheal diseases, initiating disease in the small intestines.

    Although expressed in different enviroments, these fimbriae share basic structural and biomechanical features. Structurally, they are all long (1-4 μm), thin (7-8 nm diameter) helix-like filaments that extend from the bacterial surface. Biomechanically, they share the ability to be extended into a thinner filament (2-3 nm diameter) by unwinding of the helical filament under a constant force. However, the force required to unwind is specific to each fimbrial type. In addition, the dependence of the force required to unwind a fimbria on the velocity of this unwinding, (that is, the kinetics of unwinding), is also type-specific and highly variable. These biomechanical parameters are dissimilar for UPEC and ETEC expressed fimbriae, separating them into two distinct groups. Using force spectroscopy data, helical reconstructions from electron microscopy data, and computational simulations, we show in this work how these pronounced biomechanical differences may be beneficial for bacterial survival in a given environment.

  • 43.
    Mortezaei, Narges
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Singh, Bhupender
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Uhlin, Bernt Eric
    Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS). Umeå University, Faculty of Medicine, Department of Molecular Biology (Faculty of Medicine).
    Savarino, Stephen
    Bullitt, Esther
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Antibodies Change the Mechanics of Adhesion Fimbriae: a Case Study of CS20 Fimbriae Expressed by Enterotoxigenic Escherichia Coli2015In: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 108, p. 602-Article in journal (Other academic)
    Abstract [en]

    Enterotoxigenic Escherichia coli (ETEC) express a variety of fimbriae that mediate adhesion to host epithelial cells. It has been shown that the ability of a fimbriated bacterial cell to attach and stay attached to host cells does not merely depend on the adhesin expressed distal of the fimbriae but also the biomechanical properties of the fimbriae are vital for sustained adhesion. Fimbriae can significantly extend under a constant force when exposed to an external force and therefore reduce the load on the adhesin, which is believed to help bacteria to withstand external forces applied by various body defense systems. Thus, it is thought that the fimbrial shaft and adhesin have co-evolved for optimal function when bacteria attach to host cells. To investigate if antibodies, normally found in the intestines, affects the biomechanical properties of fimbriae, we exposed CS20 fimbriae expressed by ETEC to anti-fimbrial antibodies and measured these properties using optical tweezers force spectroscopy. Our data show a change in the force required to extend the fimbriae and that the elasticity is significantly reduced by the presence of antibodies. The reduced elasticity, likely due to cross-linking of fimbrial subunits, could thus be another assignment for antibodies; in addition to their mission in marking bacteria as foreign, our data indicate that antibodies physically compromise fimbrial function. To further confirm interaction of antibodies to their specific target we performed western blot analysis, transmission electron microscopy and immunofluoresence microscopy. In the presence of antibodies, we suggest that our assay and results will be a starting point for further studies aimed at inhibiting bacterial adhesion by antibodies.

  • 44.
    Mortezaei, Narges
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Singh, Bhupender
    Umeå University, Faculty of Science and Technology, Department of Physics. Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR).
    Zakrisson, Johan
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Bullitt, Esther
    Boston University School of Medicine, Boston, Massachusetts, USA.
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Department of Physics. Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR).
    Biomechanical and Structural features of CS2 fimbriae of Enterotoxigenic Escherichia coli 2015In: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 109, no 1, p. 49-56Article in journal (Refereed)
    Abstract [en]

    Enterotoxigenic Escherichia coli (ETEC) are a major cause of diarrhea worldwide, and infection of children in underdeveloped countries often leads to high mortality rates. Isolated ETEC express a plethora of colonization factors (fimbriae/pili), of which CFA/I and CFA/II that are assembled via the alternate chaperone pathway (ACP), are amongst the most common. Fimbriae are filamentous structures, whose shafts are primarily composed of helically arranged single pilin-protein subunits, with a unique biomechanical capability allowing them to unwind and rewind. A sustained ETEC infection, under adverse conditions of dynamic shear forces, is primarily attributed to this biomechanical feature of ETEC fimbriae. Recent understandings about the role of fimbriae as virulence factors are pointing to an evolutionary adaptation of their structural and biomechanical features. In this work, we investigated the biophysical properties of CS2 fimbriae from the CFA/II group. Homology modelling its major structural subunit CotA reveals structural clues and these are related to the niche in which they are expressed. Using optical tweezers force spectroscopy we found that CS2 fimbriae unwind at a constant force of 10 pN and have a corner velocity of 1300 nm/s, i.e., the velocity at which the force required for unwinding rises exponentially with increased speed. The biophysical properties of CS2 fimbriae assessed in this work classify them into a low-force unwinding group of fimbriae together with the CFA/I and CS20 fimbriae expressed by ETEC strains. The three fimbriae are expressed by ETEC, colonize in similar gut environments, and exhibit similar biophysical features, but differ in their biogenesis. Our observation suggests that the environment has a strong impact on the biophysical characteristics of fimbriae expressed by ETEC.

  • 45.
    Norregaard, Kamilla
    et al.
    The Niels Bohr Institute.
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Department of Physics. Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark.
    Nielsen, Peter
    Department of Cellular and Molecular Medicine, Faculty of Health and Sciences, University of Copenhagen, Copenhagen, Denmark.
    Brown, Stanley
    Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark .
    Oddershede, Lene
    Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark.
    Tethered particle analysis of supercoiled circular DNA using PNA handles2014In: Nature Protocols, ISSN 1754-2189, E-ISSN 1750-2799, Vol. 9, no 9, p. 2206-2223Article in journal (Refereed)
  • 46. Nørregaard, Kamilla
    et al.
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Nielsen, Peter E
    Brown, Stanley
    Oddershede, Lene B
    DNA Supercoiling Enhances Cooperativity and Efficiency of an Epigenetic Switch2015In: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 108, no 2, p. 188A-188AArticle in journal (Other academic)
    Abstract [en]

    Upon infection by bacteriophage λ the λ repressor protein, CI, interacts with the λ operator DNA, thereby regulating protein expression and deciding between the lysogenic and lytic state. This λ switch is a model on the basis of which epigenetic switch regulation is understood. In order to study the interaction between naturally supercoiled DNA and the DNA associating protein CI, we invented a novel assay where supercoiled circular DNA plasmids were individually tethered by peptide nucleic acid (PNA) handles [1]. We used this tethered plasmid assay for a single molecule investigation of the dynamics of supercoiled DNA and studied both the dynamics of the molecule itself and its interactions with the regulatory CI protein. The dynamics of the construct was analyzed by tracking the tethered bead. This revealed that compared with relaxed DNA, the presence of supercoils greatly enhances juxtaposition probability [2]. When CI was added to the supercoiled assay, the protein would attach to the operator sites thereby looping DNA. Our studies reveal that the efficiency and cooperativity of the epigenetic λ switch are significantly increased in the supercoiled system compared with a linear assay, thus increasing the Hill coefficient [2,3]. In contrast to other single molecule assays, the current methodology allows for studying DNA dynamics and DNA-protein interactions of DNA in its naturally supercoiled state.

  • 47. Nørregaard, Kamilla
    et al.
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sneppen, Kim
    Nielsen, Peter Eigil
    Brown, Stanley
    Oddershede, Lene B.
    DNA supercoiling enhances cooperativity and efficiency of an epigenetic switch2013In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 110, no 43, p. 17386-17391Article in journal (Refereed)
    Abstract [en]

    Bacteriophage λ stably maintains its dormant prophage state but efficiently enters lytic development in response to DNA damage. The mediator of these processes is the λ repressor protein, CI, and its interactions with λ operator DNA. This λ switch is a model on the basis of which epigenetic switch regulation is understood. Using single molecule analysis, we directly examined the stability of the CI-operator structure in its natural, supercoiled state. We marked positions adjacent to the λ operators with peptide nucleic acids and monitored their movement by tethered particle tracking. Compared with relaxed DNA, the presence of supercoils greatly enhances juxtaposition probability. Also, the efficiency and cooperativity of the λ switch is significantly increased in the supercoiled system compared with a linear assay, increasing the Hill coefficient.

  • 48.
    Rodriguez, Alvaro
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Zhang, Hanqing
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Klaminder, Jonatan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Brodin, Tomas
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Department of Physics.
    ToxId: an efficient algorithm to solve occlusions when tracking multiple animals2017In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, article id 14774Article in journal (Refereed)
    Abstract [en]

    Video analysis of animal behaviour is widely used in fields such as ecology, ecotoxicology, and evolutionary research. However, when tracking multiple animals, occlusion and crossing are problematic, especially when the identity of each individual needs to be preserved. We present a new algorithm, ToxId, which preserves the identity of multiple animals by linking trajectory segments using their intensity histogram and Hu-moments. We verify the performance and accuracy of our algorithm using video sequences with different animals and experimental conditions. The results show that our algorithm achieves state-of-the-art accuracy using an efficient approach without the need of learning processes, complex feature maps or knowledge of the animal shape. ToxId is also computationally efficient, has low memory requirements, and operates without accessing future or past frames.

  • 49.
    Rodriguez, Alvaro
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Zhang, Hanqing
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Klaminder, Jonatan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Brodin, Tomas
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Andersson, Patrik L.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Department of Physics.
    ToxTrac: a fast and robust software for tracking organisms2018In: Methods in Ecology and Evolution, ISSN 2041-210X, E-ISSN 2041-210X, Vol. 9, no 3, p. 460-464Article in journal (Refereed)
    Abstract [en]

    1. Behavioral analysis based on video recording is becoming increasingly popular within research fields such as; ecology, medicine, ecotoxicology, and toxicology. However, the programs available to analyze the data, which are; free of cost, user-friendly, versatile, robust, fast and provide reliable statistics for different organisms (invertebrates, vertebrates and mammals) are significantly limited.

    2. We present an automated open-source executable software (ToxTrac) for image-based tracking that can simultaneously handle several organisms monitored in a laboratory environment. We compare the performance of ToxTrac with current accessible programs on the web.

    3. The main advantages of ToxTrac are: i) no specific knowledge of the geometry of the tracked bodies is needed; ii) processing speed, ToxTrac can operate at a rate >25 frames per second in HD videos using modern computers; iii) simultaneous tracking of multiple organisms in multiple arenas; iv) integrated distortion correction and camera calibration; v) robust against false positives; vi) preservation of individual identification; vii) useful statistics and heat maps in real scale are exported in image, text and excel formats.

    4. ToxTrac can be used for high speed tracking of insects, fish, rodents or other species, and provides useful locomotor information in animal behavior experiments. Download ToxTrac here: https://toxtrac.sourceforge.io  (Current version v2.61).

  • 50.
    Rodriguez, Alvaro
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Zhang, Hanqing
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Wiklund, Krister
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Brodin, Tomas
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Klaminder, Jonatan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Andersson, Patrik
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Refining particle positions using circular symmetry2017In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 12, no 4, article id e0175015Article in journal (Refereed)
    Abstract [en]

    Particle and object tracking is gaining attention in industrial applications and is commonly applied in: colloidal, biophysical, ecological, and micro-fluidic research. Reliable tracking information is heavily dependent on the system under study and algorithms that correctly determine particle position between images. However, in a real environmental context with the presence of noise including particular or dissolved matter in water, and low and fluctuating light conditions, many algorithms fail to obtain reliable information. We propose a new algorithm, the Circular Symmetry algorithm (C-Sym), for detecting the position of a circular particle with high accuracy and precision in noisy conditions. The algorithm takes advantage of the spatial symmetry of the particle allowing for subpixel accuracy. We compare the proposed algorithm with four different methods using both synthetic and experimental datasets. The results show that C-Sym is the most accurate and precise algorithm when tracking micro-particles in all tested conditions and it has the potential for use in applications including tracking biota in their environment.

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