FIG. 4.

(a) Kymograph showing the temporal change of the spatial distribution of chemotactic bacteria across the channel in an L-aspartate (a strong attractant) gradient. (b) Kymograph showing the temporal change of the spatial distribution of chemotactic bacteria across the channel in case of a NiSO₄ gradient. Ni²⁺ is a strong repellent. (c) Asymmetry index (A) for bacteria in various chemical gradients. Solid blue line (dark gray in print): chemotactic (wt) bacteria in aspartate gradient, dashed blue line (dark gray in print): non-chemotactic (mutant) bacteria in aspartate gradient, solid red line (light gray in print): chemotactic bacteria in the absence of chemoeffector gradient (in buffer), and dashed green line (light gray in print): chemotactic (wt) bacteria in nickel gradient.