Professor Richard Berry D. Phil.

Abstract:

We demonstrate the use of a laser trap (‘optical tweezers’) and back-focal-plane position detector to measure rapid rotation in aqueous solution of single particles with sizes in the vicinity of 1 μm. Two types of rotation were measured: electrorotation of polystyrene microspheres and rotation of the flagellar motor of the bacterium Vibrio alginolyticus. In both cases, speeds in excess of 1000 Hz (rev s⁻¹) were measured. Polystyrene beads of diameter about 1 μm labelled with smaller beads were held at the centre of a microelectrode array by the optical tweezers. Electrorotation of the labelled beads was induced by applying a rotating electric field to the solution using microelectrodes. Electrorotation spectra were obtained by varying the frequency of the applied field and analysed to obtain the surface conductance of the beads. Single cells of V. alginolyticus were trapped and rotation of the polar sodium-driven flagellar motor was measured. Cells rotated more rapidly in media containing higher concentrations of Na⁺, and photodamage caused by the trap was considerably less when the suspending medium did not contain oxygen. The technique allows single-speed measurements to be made in less than a second and separate particles can be measured at a rate of several per minute. © 2003 Taylor & Francis Group, LLC.

Abstract:

This chapter contains sections titled: Introduction Structure Propeller and Drive‐shaft Rotor Stator Rotor–Stator Interactions Function Motor Driven by H+ and Na+ Ion Flux Torque versus Speed Independent Torque Generators Proton Motive Force, Sodium‐motive Force, Ion Flux Reversibility Steps? Models Conceptual Model Kinetic Mode Summary Introduction Structure Propeller and Drive‐shaft Rotor Stator Rotor–Stator Interactions Propeller and Drive‐shaft Rotor Stator Rotor–Stator Interactions Function Motor Driven by H+ and Na+ Ion Flux Torque versus Speed Independent Torque Generators Proton Motive Force, Sodium‐motive Force, Ion Flux Reversibility Steps? Motor Driven by H+ and Na+ Ion Flux Torque versus Speed Independent Torque Generators Proton Motive Force, Sodium‐motive Force, Ion Flux Reversibility Steps? Models Conceptual Model Kinetic Mode Conceptual Model Kinetic Mode Summary

Abstract:

Abstract The bacterial flagellar motor is a rotary molecular motor situated in the cell envelopes of bacteria that is driven by a flow of charged ions across the bacterial plasma membrane. The motor powers the rotation of helical flagellar filaments so that bacteria swim, frequently towards a more favourable location.