title: Applying torque to the Escherichia coli flagellar motor using magnetic tweezers.
abstract: The bacterial flagellar motor of Escherichia coli is a nanoscale rotary engine essential for bacterial propulsion. Studies on the power output of single motors rely on the measurement of motor torque and rotation under external load. Here, we investigate the use of magnetic tweezers, which in principle allow the application and active control of a calibrated load torque, to study single flagellar motors in Escherichia coli. We manipulate the external load on the motor by adjusting the magnetic field experienced by a magnetic bead linked to the motor, and we probe the motor's response. A simple model describes the average motor speed over the entire range of applied fields. We extract the motor torque at stall and find it to be similar to the motor torque at drag-limited speed. In addition, use of the magnetic tweezers allows us to force motor rotation in both forward and backward directions. We monitor the motor's performance before and after periods of forced rotation and observe no destructive effects on the motor. Our experiments show how magnetic tweezers can provide active and fast control of the external load while also exposing remaining challenges in calibration. Through their non-invasive character and straightforward parallelization, magnetic tweezers provide an attractive platform to study nanoscale rotary motors at the single-motor level.
authors.affiliation: Department of Bionanoscience, Kavli Institute of Nanoscience, Delft University of Technology, van der Maasweg 9, 2629 HZ Delft, The Netherlands.
authors.forename: Maarten M
authors.initials: MM
authors.lastname: van Oene
authors.affiliation: Department of Bionanoscience, Kavli Institute of Nanoscience, Delft University of Technology, van der Maasweg 9, 2629 HZ Delft, The Netherlands.
authors.forename: Laura E
authors.initials: LE
authors.lastname: Dickinson
authors.affiliation: Department of Bionanoscience, Kavli Institute of Nanoscience, Delft University of Technology, van der Maasweg 9, 2629 HZ Delft, The Netherlands.
authors.forename: Bronwen
authors.initials: B
authors.lastname: Cross
authors.affiliation: Department of Bionanoscience, Kavli Institute of Nanoscience, Delft University of Technology, van der Maasweg 9, 2629 HZ Delft, The Netherlands.
authors.forename: Francesco
authors.initials: F
authors.lastname: Pedaci
authors.affiliation: Department of Physics, Nanosystems Initiative Munich, and Center for NanoScience, LMU Munich, Amalienstrasse 54, 80799 Munich, Germany.
authors.forename: Jan
authors.initials: J
authors.lastname: Lipfert
authors.affiliation: Department of Bionanoscience, Kavli Institute of Nanoscience, Delft University of Technology, van der Maasweg 9, 2629 HZ Delft, The Netherlands.
authors.forename: Nynke H
authors.initials: NH
authors.lastname: Dekker
mesh_terms: D001431:Bacteriological Techniques / Q000379:methods; D004926:Escherichia coli / Q000502:physiology* / Q000528:radiation effects*; D005407:Flagella / Q000502:physiology* / Q000528:radiation effects*; D060526:Magnetic Fields; D009038:Motion; D013314:Stress, Mechanical; D019415:Torque