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.

The bank of swimming organisms at the micron scale (BOSO-Micro)

“…attached micrometer beads to flagella to measure the motor torque to be 1260 ± 190 pNnm [ 79 ]. In magnetic tweezers experiments involving the attachment of paramagnetic beads, the corresponding torque amounted to 874 ± 206 pNnm [ 80 ]. In contrast, a simplified theoretical model predicts a lower value of 370 ± 100 pNnm [ 81 ] while recent numerical simulations reported values in the range 440 − 820 pNnm [ 82 ].…”

Surface Sensing and Adaptation in Bacteria

“…A similar phenomenon was observed in B. subtilis, where EpsE, a glycosyl transferase involved in EPS biosynthesis, acts inside bacterial cells as a molecular clutch to stop flagellar rotation (65). (193), microfluidics (144), optical and magnetic tweezers (206), and force measurements (30)] combined with genetic tools and careful examinations at short timescales will hopefully unlock some of the secrets of bacterial mechanosensation. On a molecular level we will need to address how force modulates the function of specific proteins or protein complexes and what the consequences are in terms of signaling.…”

Remotely actuated polymeric nanocomposites for biomedical applications

“…This beads can be further superficially functionalised (with biotin, streptavidin, fluorescent dyes, hydroxyapatite, amino and carboxy groups, etc.) for many applications such as in the study of the Escherichia coli flagellar motor using magnetic tweezers [152,155] by attaching a bead to the hook of the flagellar motors to probe the motor's average speed, as well as reducing the average speed of the motors until they stall, by increasing #» B strength from 1 to 20 mT [155]. Similarly, biomagnetic separation is a technique frequently used for purification, sorting, etc.…”