| Summary: | 碩士 === 國立中央大學 === 物理學系 === 101 === Escherichia coli use flagellar motors to swim. This tiny molecular machine is powered by proton flux through proton-motive force. The cells can be propelled by 4-8 left-handed helical flagellar filaments in one cell. When all of the motors rotate counterclockwise (CCW), the filaments can form a bundle to propel the cells forward. When one or more motors switch to clockwise (CW), their filaments will move out of the bundle and change the direction of the cells. The switching rate of the motor is modulated by the signal transduction molecules CheY binding to the motor. However, the external loading will affect the switching rate. For large number cell average, the CCW/CW switching rates depend on load. However, the CheY concentration and motor driving are different from cell to cell. Here, we examine the two motor switching rates at different external loads in one cell to eliminate the cellular CheY concentration and proton-motive force variations. We use high speed camera (~957 fps) to monitor two different size of beads attached to the motors in single cell. In our limited data, the switching rate is independent on the external load in high load region.
Appling the high speed camera method to monitoring the rotation of multiple flagellar motors, we can also test possibility of coordinated switching of bacterial flagellar motors. On contrary to the previous report, we directly measure the rotation of two flagellar motors. We did not find high rotational correlation between neighboring motors.
We also use the same method, high speed camera, to observe the proton-motive force of multiple cells, we add the ethanol and the ionophore (CCCP) to the motility medium and observed cells how fast did cells died. We can record rotational speed of the tethered cells and we can know the relationship between the rotational speed and the times. The rotation of bacterial flagellar motor is a direct indication of proton motive force.
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