Figure 2.

Track of a typical untreated E. coli cell (upper panel) with combined phase-contrast and fluorescence images (dark and light, respectively, lower-left panel). For cells of all kinds, runs are shown in blue, tumbles are in red, and runs with the laser on are in green. Each data point along the trajectory corresponds to one video frame (30/s). At the start, image 1 (lower-left panel), the phase-contrast image shows the cell moving parallel to the X-Y image plane. Cell-body measurements were made from this image. At image 68, the cell is seen end-on while moving along the Z axis at track point 68. The overview (right panel) shows the track in the X-Y plane from points 100–200, and includes laser illumination points 157–191. The cell was running with a tight bundle in image 161. A tumble occurred during points 168–177. In image 177, as the tumble ended, the bundle started to reform, a process that was completed at point 188 (not shown). A tightly formed bundle is evident in image 191. After this point, another tumble began. The scale bar here and in all other figures is 2 μm.