Observed asymmetric trajectory

The motion of singly flagellated Vibrio alginolyticus bacterial cells was ob-served (Kudo et al. 2005). Figure 2 shows a dark-field microscope image of a cell. The flagellum is attached to one end (pole) of the cell body. The motions of three strains of V. alginolyticus were compared. Wild type YM4 cells swim forward and backward according to the rotational direction of the flagellum

YM42 cells almost always swim forward, and NMB102 cells almost always swim backward (Table 1). A drop of each cell suspension was sealed between a glass slide and a cover slip, the distance between which is estimated to be about 7 jum. The samples were observed with a high-intensity dark-field microscope, enabling the flagellum to be observed. Figure 3(a) shows a typical example of swimming traces for a YM4 cell. Initially, the cell moves clockwise (the lower part of the trace) and travels straight in the eleven o'clock direction, then turns counterclockwise. Figure 3(b) is the same trace with a time interval of 0.1 s. In this figure, it is apparent whether the cell swims forward or backward since the flagellum is clearly

Typical examples of swimming traces of V. alginolyticus cells observed with a dark-field microscope. Trace of a wild type cell is shown (a) continuously for 1.2 s and (b) at 0.1 s intervals. Trace of a smooth-swimming mutant cell is shown (c) con-tinuously for 0.6 s and (d) at 0.1 s intervals. Trace of an inverse smooth-swimming mutant cell is shown (e) continuously for 0.7 s and (f) at 0.1 s intervals. The arrows indicate the swimming direction. From Kudo et al. (2005) with permission