Figure 4.

Orientation of the cell during twitching. Angular correlation function between the velocity of the cell and the axis connecting two spheres of the cell body. There is a noticeable preference toward the 90° angle. The effect of orientation is more pronounced for the BSA-coated surface, as explained in the text. Coating with poly-L-lysine has no visible effect on correlations that are similar to the case of the DMEM medium (see Materials and Methods). (Inset) Orientation of the cell obtained from numerical simulations of the two-dimensional model of twitching bacteria for two types of surfaces differing in the pili attachment probability A.