Application of magnetic torque on the bacterial flagellar motor

Thesis

There is a strong need to develop a mechanical method to apply external torque to the bacterial flagellar motor. Such a method will allow us to probe the behaviour of the motor at a range of different speeds under different external conditions.

In this thesis, I explored various methods to deliver torque at the single-molecule level, in particular the use of angular optical trapping and magnetic tweezers. I have identified rutile particles as suitable handles for use in angular optical trapping due to their high birefringence. Further progress was not achieved using angular optical trapping due to the lack of a suitable method to attach birefringent particles to the bacterial flagellar motor. On the other hand, I was able to make further progress using magnetic tweezers. A highly-reproducible and high-yielding magnetic bead assay was developed along with electromagnets capable of generating fast-rotating magnetic fields at magnitudes on the order of tens of mT.

Using the system of delivering magnetic torque developed, I was able to stall and rotate the motor forward at speeds up to 220 Hz and in the reverse direction. Stalling experiments carried out on the motor revealed the stator mechanosensing depends on torque and not rotation. Signatures of stators dropping out at low load experiments further confirm the load dependence of stators.

Authors: Lim, R

• Publication date: 2015
• DOI: 10.5287/ora-w4vaqma26
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: Oxford University, UK
• Language: English
• Keywords: electromagnetic tweezers; bacterial flagellar motor; Single-molecule biophysics
• Subjects: Microbiology; Condensed Matter Physics; Molecular biophysics (biochemistry)