Figure 5.

Tracks for B. subtilis DS9540. (A) A heavily flagellated cell executing a relatively straight track. The period of laser illumination (points 65–94) occurred during a run. Image 53 shows the cell body in bright phase, though slightly out of focus. At the start of laser illumination, the cell was running with a tight bundle (image 68). At 0.1 s later, the bundle began to loosen (image 71). In the video, the cell began to wobble and the track’s helicity increased (points 120–180). Although this cell did not tumble, the laser deenergized the cell and affected its motility. This is evident in the slowing speed from points 120–180. (B) Another heavily flagellated but shorter cell. This cell swam with a typical run-and-tumble trajectory. At trajectory point 120, a data point was dropped, which caused doubling of the speed (the peak in the speed graph). During laser illumination (track points 137–173), the cell initially ran with a tight bundle (image 143), but the bundle began to loosen (image 152). At track points 156–158, the cell tumbled, as evident in image 158, but individual filaments could not be resolved. Image 159 shows the cell body moving along a new trajectory, even though the filaments had not formed a tight bundle. This cell tumbled again from track points 161–172 and the cell slowed (speed trace 150–180), after which time the cell swam at the original speed.