Fig. 8.

Spatial information increases with the steepness of an exponential gradient. Chemotaxis was simulated in exponential gradients that start at 1×10^− 9 M aspartate and end at concentrations between 1×10^− 9 and 1×10^− 6 M (in the center of the arena). The greater the end (maximum) concentration, the steeper the gradient. The information in the trajectories increased at increasingly steep gradients up to 5×10^− 7 M, which is the limit of the responsiveness with the infectivity value used (see Materials and methods). Beyond this, the receptors on the bacterium become increasingly saturated, i.e., they are saturated over an increasingly large fraction of the arena, and the information in the trajectory decreases