FBS Colloquia No.273Laboratory of Nano-Biophysics

Direction-dependent rotational fluctuation of bacterial flagellar motor

Escherichia coli cell swims in liquid environment by their locomotive organelle flagella. The flagellum of E. coli consists of a rotary motor embedded in the cytoplasmic membrane, a flagellar filament that acts as a screw, and a universal joint hook that connects the filament to the motor. E. coli cell has six to eight flagella in a cell. When the motors rotate counterclockwise (CCW rotation), the flagella are wound to single flagellar bundle and the cell swims in a straight, whereas when they rotate clockwise, the flagella are unwound from the flagellar bundle and the cell changes its swimming direction. In our research group, small polystyrene bead was attached to the flagellar filaments, and the rotational motion of bead was followed with a high-speed CCD camera to obtain a time-trace of the rotational velocity and direction (bead assay). By applying this assay, we found that the rotation of the flagellar motor fluctuated more when rotating CCW direction than when rotating CW direction. In this presentation, we will present our recent results on the direction-dependent rotational fluctuation of the flagellar motor of E. coli, including the detailed analysis of the fluctuation itself by using a high-speed camera with high temporal resolution.