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  • 1.
    Alakpa, Enateri V.
    et al.
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB).
    Bahrd, Anton
    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.
    Novikov, Lev N.
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB).
    Ljungberg, Christina
    Umeå University, Faculty of Medicine, Department of Surgical and Perioperative Sciences, Hand Surgery.
    Kelk, Peyman
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB).
    Bioprinted schwann and mesenchymal stem cell co-cultures for enhanced spatial control of neurite outgrowth2023In: Gels, E-ISSN 2310-2861, Vol. 9, no 3, article id 172Article in journal (Refereed)
    Abstract [en]

    Bioprinting nerve conduits supplemented with glial or stem cells is a promising approach to promote axonal regeneration in the injured nervous system. In this study, we examined the effects of different compositions of bioprinted fibrin hydrogels supplemented with Schwann cells and mesenchymal stem cells (MSCs) on cell viability, production of neurotrophic factors, and neurite outgrowth from adult sensory neurons. To reduce cell damage during bioprinting, we analyzed and optimized the shear stress magnitude and exposure time. The results demonstrated that fibrin hydrogel made from 9 mg/mL of fibrinogen and 50IE/mL of thrombin maintained the gel’s highest stability and cell viability. Gene transcription levels for neurotrophic factors were significantly higher in cultures containing Schwann cells. However, the amount of the secreted neurotrophic factors was similar in all co-cultures with the different ratios of Schwann cells and MSCs. By testing various co-culture combinations, we found that the number of Schwann cells can feasibly be reduced by half and still stimulate guided neurite outgrowth in a 3D-printed fibrin matrix. This study demonstrates that bioprinting can be used to develop nerve conduits with optimized cell compositions to guide axonal regeneration.

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  • 2.
    Andersson, Magnus
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Axner, Ove
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Almqvist, Fredrik
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Uhlin, Bernt Eric
    Umeå University, Faculty of Medicine, Department of Molecular Biology (Faculty of Medicine).
    Fällman, Erik
    Umeå University, Faculty of Science and Technology, Department of 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.

  • 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
    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)
  • 4.
    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)
  • 5.
    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.

  • 6.
    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.

  • 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.
    Characterization of S pili — investigation of their mechanical properties2007Manuscript (preprint) (Other (popular science, discussion, etc.))
  • 8.
    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)
  • 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.
    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.

  • 10.
    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.

  • 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, 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.

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  • 13.
    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)
  • 14.
    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.

  • 15.
    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.

  • 16.
    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.

  • 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, 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.

  • 18.
    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.

  • 19. Baker, Joseph
    et al.
    Dahlberg, Tobias
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Bullitt, Esther
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Impact of an alpha helix and a cysteine-cysteine disulfide bond on the resistance of bacterial adhesion pili to stress2021In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 118, no 21, article id e2023595118Article in journal (Refereed)
    Abstract [en]

    Escherichia coli express adhesion pili that mediate attachment to host cell surfaces and are exposed to body fluids in the urinary and gastrointestinal tracts. Pilin subunits are organized into helical polymers, with a tip adhesin for specific host binding. Pili can elastically unwind when exposed to fluid flow forces, reducing the adhesin load, thereby facilitating sustained attachment. Here we investigate biophysical and structural differences of pili commonly expressed on bacteria that inhabit the urinary and intestinal tracts. Optical tweezers measurements reveal that Class 1a pili of uropathogenic E. coli (UPEC), as well as Class 1b of enterotoxigenic E. coli (ETEC), undergo an additional conformational change beyond pilus unwinding, providing significantly more elasticity to their structure than ETEC Class 5 pili. Examining structural and steered molecular dynamics simulation data, we find this difference in Class 1 pili subunit behavior originates from an alpha-helical motif that can unfold when exposed to force. A disulfide bond cross-linking beta-strands in Class 1 pili stabilizes subunits, allowing them to tolerate higher forces than Class 5 pili that lack this covalent bond. We suggest that these extra contributions to pilus resiliency are relevant for the UPEC niche since resident bacteria are exposed to stronger, more transient drag forces compared to those experienced by ETEC bacteria in the mucosa of the intestinal tract. Interestingly, Class 1b ETEC pili include the same structural features seen in UPEC pili, while requiring lower unwinding forces that are more similar to those of Class 5 ETEC pili.

  • 20. Baker, Joseph
    et al.
    Dahlberg, Tobias
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Bullitt, Esther
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Unveiling the Contributions of Secondary Structure and Disulfide Bonds for Bacterial Adhesion Pili Extension using a Multiscale Approach2021Conference paper (Other academic)
    Abstract [en]

    Bacterial adhesion pili are essential virulence factors for many pathogenic Escherichia coli, including bacteria that cause urinary tract infections (UPEC) and diarrheal diseases (ETEC). To sustain adhesion under forces similar to those in the fluid environments of the urinary tract and gastrointestinal tract, these pili (also called fimbriae) can extend to over seven times their original length. Both UPEC and ETEC can uncoil their quaternary structure under pulling force and re-coil to their helical form when the force is reduced, as observed using optical tweezers. However, after extension to a linear polymer UPEC undergo an additional reversible conformational change, that is not seen in ETEC. The mechanism for this conformational change in UPEC is not known. Therefore, to obtain a comprehensive picture of pilus extension we have taken a synergistic approach that combines optical tweezer experiments, structural data from cryo-EM, and steered molecular dynamics simulations to investigate the response of pilin subunits to force.

    Our multi-faceted approach provides novel molecular-scale insights into the structural changes that occur in UPEC and ETEC pili under pulling forces. We find that the conformational change observed in UPEC pili in optical tweezer experiments is correlated with the presence of an alpha helix. In addition, structural analysis and steered molecular dynamics simulations show that there is a disulfide bond that provides additional stability of UPEC pilin subunits that is not observed in ETEC pilins, which lack cysteine residues. Together, these results suggest that the mechanism of extension of bacterial adhesion pili is related to their environmental niche, and the magnitude of fluid forces in the urinary tract versus the GI tract.

  • 21. 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.

  • 22.
    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.

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  • 23.
    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.

  • 24.
    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.

  • 25.
    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)
  • 26.
    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)
  • 27.
    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.

  • 28.
    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.

  • 29.
    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.

  • 30.
    Dahlberg, Tobias
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Optical design for laser tweezers Raman spectroscopy setups for increased sensitivity and flexible spatial detection2021In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 60, no 16, p. 4519-4523Article in journal (Refereed)
    Abstract [en]

    We demonstrate a method to double the collection efficiency in Laser Tweezers Raman Spectroscopy (LTRS) by collecting both the forward and back-scattered light in a single-shot multitrack measurement. Our method can collect signals at different sample volumes, granting both the pinpoint spatial selectivity of confocal Raman and the bulk sensitivity of non-confocal Raman simultaneously. Further, we display that our approach allows for reduced detector integration time and laser power. To show this, we measure the Raman spectra of both polystyrene beads and bacterial spores. For spores, we can trap them at 2.5 mW laser power and acquire a high signal-to-noise ratio Power spectrum of the CaDPA peaks using an integration time of 2 x 30 seconds. Thus, our method will enable the monitoring of biological samples sensitive to high intensities for longer times. Additionally, we demonstrate that by a simple modification, we can add polarization sensitivity and retrieve extra biochemical information. 

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  • 31.
    Dahlberg, Tobias
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Baker, Joseph
    Department of Chemistry, The College of New Jersey, Ewing, New Jersey.
    Bullitt, Esther
    Department of Physiology & Biophysics, Boston University School of Medicine, Boston, Massachusetts.
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Department of Physics. Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR).
    Unveiling molecular interactions that stabilize bacterial adhesion pili2022In: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 121, no 11, p. 2096-2106Article in journal (Refereed)
    Abstract [en]

    Adhesion pili assembled by the chaperone-usher pathway are superelastic helical filaments on the surface of bacteria, optimized for attachment to target cells. Here, we investigate the biophysical function and structural interactions that stabilize P pili from uropathogenic bacteria. Using optical tweezers, we measure P pilus subunit-subunit interaction dynamics and show that pilus compliance is contour-length dependent. Atomic details of subunit-subunit interactions of pili under tension are shown using steered molecular dynamics (sMD) simulations. sMD results also indicate that the N-terminal “staple” region of P pili, which provides interactions with pilins that are four and five subunits away, significantly stabilizes the helical filament structure. These data are consistent with previous structural data, and suggest that more layer-to-layer interactions could compensate for the lack of a staple in type 1 pili. This study informs our understanding of essential structural and dynamic features of adhesion pili, supporting the hypothesis that the function of pili is critically dependent on their structure and biophysical properties.

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  • 32.
    Dahlberg, Tobias
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Baker, Joseph
    Dept of Chemistry, The College of New Jersey.
    Bullitt, Esther
    Dept of Physiology & Biophysics, Boston University School of Medicine.
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Unveiling molecular interactions that stabilize the chaperone-usher pili rod and their role for mechanical and kinetic propertiesManuscript (preprint) (Other academic)
  • 33.
    Dahlberg, Tobias
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Malyshev, Dmitry
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Andersson, Per Ola
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Biophysical Fingerprinting of Single Bacterial Spores using Laser Raman Optical Tweezers2020In: Proceedings Volume 11416, Chemical, Biological, Radiological, Nuclear, and Explosives (CBRNE) Sensing XXI, 2020, SPIE - International Society for Optical Engineering, 2020, article id 1141601Conference paper (Refereed)
    Abstract [en]

    Spore-forming bacteria that cause diseases pose a danger in our society. When in spore form, bacteria can survive high temperatures and resist a plethora of disinfection chemicals. Effective disinfection approaches are thus critical. Since a population of bacterial spores is heterogeneous in many aspects, single spore analyzing methods are suitable when heterogeneous information cannot be neglected. We present in this work a highresolution Laser Raman optical tweezers that can trap single spores and characterize their Raman spectra. We first evaluate our system by measuring Raman spectra of spores, and purified DNA and DPA. Thereafter, we expose Bacillus thuringiensis spores to peracetic acid, chlorine dioxide, and sodium hypochlorite, which are common disinfection chemicals. The data reveals how these agents change the constitutes of a spore over time, thus improving on the mode of action of these disinfection chemicals.

  • 34.
    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, 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.

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  • 35. Doran, Matthew
    et al.
    Dahlberg, Tobias
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Baker, Joseph
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Bullitt, Esther
    CS20 bridge the gap between class 1 and class 5 bacterial adhesion pili2022In: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 121, no 3, suppl. 1, p. 168a-168a, article id 817-PlatArticle in journal (Refereed)
    Abstract [en]

    Enterotoxigenic Escherichia coli (ETEC) are pathogenic bacteria that cause diarrheal disease that disrupts the nutrition and the growth of children under the age of 5 and causes illness in travelers to countries where these bacteria are endemic. ETEC express long thin helical filaments on their surface, ∼1 micron long and 8 nm in diameter, called pili or fimbriae. Often essential virulence factors, these filaments, including ETEC CS20 pili, are composed of approximately 1,000 copies of the major pilin protein and one copy of a tip protein that provides binding specificity. While the structures of ETEC pili from different strains are similar, there are critical differences that alter their biophysical properties.

    ETEC express Class 1 and/or Class 5 pilins. The Class 1 CS20 pilin, CsbA, is genetically similar to FimA from Type 1 pili that are expressed on many strains of Escherichia coli, including bacteria that infect the urinary tract or the gastrointestinal tract, and also to PapA pilins expressed on bacteria that infect the kidneys. Thus, despite CS20 being expressed on ETEC, its pilin is genetically distant from the Class 5 CFA/I pilin, CfaB, the most commonly expressed ETEC pilin.

    We show here the three-dimensional structure and surface coulombic charge of CS20 pili, determined at 3.4 Å resolution by electron cryomicroscopy (cryo-EM). Our force spectroscopy data show that CS20 pili have a helix unwinding force that is twice that of CFA/I pili, and half that of Type 1 pili. Molecular dynamics simulations are further used to unveil features along the unwinding pathway at an atomistic scale. We see that CS20 pili bridge the genetic and environmental gap between Class 1 and Class 5 adhesion pili that are expressed on pathogenic bacteria.

  • 36.
    Doran, Matthew H.
    et al.
    Department of Physiology & Biophysics, Boston University Chobanian & Avedisian School of Medicine, Boston, USA.
    Baker, Joseph L.
    Department of Chemistry, The College of New Jersey, Ewing, USA.
    Dahlberg, Tobias
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Bullitt, Esther
    Department of Physiology & Biophysics, Boston University Chobanian & Avedisian School of Medicine, Boston, USA.
    Three structural solutions for bacterial adhesion pilus stability and superelasticity2023In: Structure, ISSN 0969-2126, E-ISSN 1878-4186Article in journal (Refereed)
    Abstract [en]

    Bacterial adhesion pili are key virulence factors that mediate host-pathogen interactions in diverse epithelial environments. Deploying a multimodal approach, we probed the structural basis underpinning the biophysical properties of pili originating from enterotoxigenic (ETEC) and uropathogenic bacteria. Using cryo-electron microscopy we solved the structures of three vaccine target pili from ETEC bacteria, CFA/I, CS17, and CS20. Pairing these and previous pilus structures with force spectroscopy and steered molecular dynamics simulations, we find a strong correlation between subunit-subunit interaction energies and the force required for pilus unwinding, irrespective of genetic similarity. Pili integrate three structural solutions for stabilizing their assemblies: layer-to-layer interactions, N-terminal interactions to distant subunits, and extended loop interactions from adjacent subunits. Tuning of these structural solutions alters the biophysical properties of pili and promotes the superelastic behavior that is essential for sustained bacterial attachment.

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  • 37.
    Enevold, Jenny
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Dahlberg, Tobias
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Stangner, Tim
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Tang, Shi
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Lindh, E. Mattias
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Gracia-Espino, Eduardo
    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.
    Tunable two-dimensional patterning of a semiconducting Nanometer-Thin C60 fullerene film using a spatial light modulator2020In: ACS Applied Nano Materials, ISSN 2574-0970, Vol. 3, no 6, p. 2574-0970Article in journal (Other academic)
    Abstract [en]

    The photochemical coupling of fullerene molecules into covalently connected oligomeric or polymeric structures can result in drastically lowered solubility in common solvents with retained semiconductor properties. Here, we exploit this combination of properties for the utilization of fullerenes as a negative photoresist material with electronic functionality. Specifically, we develop an easily tunable exposure system, essentially comprising a laser and a computer-controlled spatial light modulator (SLM) featuring >8 million independently controlled pixels, for the spatially selective photochemical transformation of nanometer-thin C60 fullerene films. With a carefully designed laser-SLM-exposure/solvent-development cycle, we are able to realize well-resolved two-dimensional hexagonal or square patterns of circular C60 microdots with a center-to-center distance of 1–5 μm and a maximum thickness of 20–35 nm over several square-millimeter-sized areas on a substrate. The functionality of such a hexagonal C60 pattern was demonstrated by its inclusion in between the transparent electrode and the active material in a light-emitting electrochemical cell, which featured an enhanced light output by >50% in comparison to a reference device void of the patterned C60 layer.

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  • 38.
    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)
  • 39.
    Escamez, Sacha
    et al.
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    André, Domenique
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Sztojka, Bernadette
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC). Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Bollhöner, Benjamin
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Hall, Hardy
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Berthet, Béatrice
    Voss, Ute
    Lers, Amnon
    Maizel, Alexis
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Bennett, Malcolm
    Tuominen, Hannele
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC). Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Cell Death in Cells Overlying Lateral Root Primordia Facilitates Organ Growth in Arabidopsis2020In: Current Biology, ISSN 0960-9822, E-ISSN 1879-0445, Vol. 30, no 3, p. 455-464Article in journal (Refereed)
    Abstract [en]

    Plant organ growth is widely accepted to be determined by cell division and cell expansion, but, unlike that in animals, the contribution of cell elimination has rarely been recognized. We investigated this paradigm during Arabidopsis lateral root formation, when the lateral root primordia (LRP) must traverse three overlying cell layers within the parent root. A subset of LRP-overlying cells displayed the induction of marker genes for cell types undergoing developmental cell death, and their cell death was detected by electron, confocal, and light sheet microscopy techniques. LRP growth was delayed in cell-deathdeficient mutants lacking the positive cell death regulator ORESARA1/ANAC092 (ORE1). LRP growth was restored in ore1-2 knockout plants by genetically inducing cell elimination in cells overlying the LRP or by physically killing LRP-overlying cells by ablation with optical tweezers. Our results support that, in addition to previously discovered mechanisms, cell elimination contributes to regulating lateral root emergence.

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  • 40.
    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)
  • 41.
    Fällman, Erik
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    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.
    Jass, Jana
    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.
    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)
  • 42.
    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)
  • 43.
    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
    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.
    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

  • 44.
    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.

  • 45.
    Jonsmoen, Unni Lise
    et al.
    Department of Paraclinical Sciences, Faculty of Veterinary Medicine, Norwegian University of Life Sciences (NMBU), Ås, Norway.
    Malyshev, Dmitry
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Öberg, Rasmus
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Dahlberg, Tobias
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Aspholm, Marina E.
    Department of Paraclinical Sciences, Faculty of Veterinary Medicine, Norwegian University of Life Sciences (NMBU), Ås, Norway.
    Andersson, Magnus
    Umeå University, Faculty of Science and Technology, Department of Physics. Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR).
    Endospore pili - flexible, stiff and sticky nanofibers2023In: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 122, no 13, p. 2696-2706Article in journal (Refereed)
    Abstract [en]

    Species belonging to the Bacillus cereus group form endospores (spores) whose surface is decorated with micrometers-long and nanometers-wide endospore appendages (Enas). The Enas have recently been shown to represent a completely novel class of Gram-positive pili. They exhibit remarkable structural properties making them extremely resilient to proteolytic digestion and solubilization. However, little is known about their functional and biophysical properties. In this work, we apply optical tweezers to manipulate and assess how wild type and Ena-depleted mutant spores immobilize on a glass surface. Further, we utilize optical tweezers to extend S-Ena fibers to measure their flexibility and tensile stiffness. Finally, by oscillating single spores, we examine how the exosporium and Enas affect spores’ hydrodynamic properties. Our results show that S-Enas (μm long pili) are not as effective as L-Enas in immobilizing spores to glass surfaces but are involved in forming spore to spore connections, holding the spores together in a gel-like state. The measurements also show that S-Enas are flexible but tensile stiff fibers, which support structural data suggesting that the quaternary structure is composed of subunits arranged in a complex to produce a bendable fiber (helical turns can tilt against each other) with limited axial fiber extensibility. Lastly, the results show that the hydrodynamic drag is 1.5-times higher for wild type spores expressing S- and L-Enas compared to mutant spores expressing only L-Enas or ”bald spores” lacking Ena, and 2-times higher compared to spores of the exosporium deficient strain. This study unveils novel findings on the biophysics of S- and L-Enas, their role in spore aggregation, binding of spores to glass, and their mechanical behavior upon exposure to drag forces.

  • 46.
    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.

  • 47.
    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, E-ISSN 2159-7081, Vol. 4, no 1, article id e27517Article 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.

  • 48.
    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.

  • 49.
    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)
  • 50.
    Lindberg, Ann-Sofie
    et al.
    Winternet.
    Wiklund, Krister
    Andersson, Magnus
    Malm, Christer B.
    Firefighters' fit for duty score-model: Book of Abstracts2016In: 21st Annual Congress of the European College of Sport Science: Crossing borders through sport science, ECSS , 2016, article id 2322Conference paper (Other academic)
    Abstract [en]

    Physical capacity has previously been deemed important for firefighters’ physical work capacity, and evaluation of fitness for duty is common in the pre-hiring process. Various methods have been used to establish cut-off limits, i.e. normative data or expert judges. In accordance with government regulation, both full-time and part-time firefighters in Sweden have to pass a medical examination and a test of physical work capacity for permission to execute smoke diving. The physical work capacity test is a pass or fail test: dressed in firefighting protective clothes and breathing apparatus (total weight 24 ± 0.5 kg), six minutes walking with the incline at 8 degrees and treadmill speed of 4.5 km/h is performed. Inclusion of additional physical tests and appropriate cut-off limits is a decision taken by each individual municipality. The aim of the present study was to create a score model for evaluation of fitness for duty in the pre-hiring process of firefighters. Methods A total of 128 (64 men and 64 women) subjects: full-time firefighters, part-time firefighters and civilians, were included. Subjects performed five simulated firefighting work tasks and a selected battery six of physical tests including; 500 m rowing, grip strength, endurance bench press, track running 3000 m, standing broadjump and upright barbell row. The combined information from subjective evaluated cut-off limits, breakpoint estimation, checkpoint estimation and percentiles were used to create a score-model MO-PM30 Performance: Mixed Session 424 21ST ANNUAL CONGRESS OF THE EUROPEAN COLLEGE OF SPORT SCIENCE for evaluation of fit for duty. Results The models yielded various cut-off limits on the same physical test, depending on the work task investigated, but all tests were scored on a 1-11 scale. Consequently, the maximum total score was 66 and the minimum total score was 6. The recommended minimum total score of six tests is 36. Discussion In this study we created a score-model for evaluation of firefighters’ fit for duty in the pre-hiring process. When pre-hiring physical tests are performed, an easily conducted battery of physical tests is important in order to reduce costs but still maintain high validity and reliability. The score-model is easy to understand, performance gives the same score irrespectively of age and sex and makes it possible for the aspirants to prepare for the included physical tests. Since a specific physical test differs in importance in the prediction of simulated work task performance, the lack of performance in one physical test may not be fully compensated with a higher performance in another physical test. Simplifying and generalizing a method makes it practically usable at the detriment of accuracy on an individual level.

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