  Swimming bacteria detect chemical gradients by performing temporal
comparisons of recent measurements of chemical concentration. These comparisons
are described quantitatively by the chemotactic response function, which we
expect to optimize chemotactic behavioral performance. We identify two
independent chemotactic performance criteria: in the short run, a favorable
response function should move bacteria up chemoattractant gradients, while in
the long run, bacteria should aggregate at peaks of chemoattractant
concentration. Surprisingly, these two criteria conflict, so that when one
performance criterion is most favorable, the other is unfavorable. Since both
types of behavior are biologically relevant, we include both behaviors in a
composite optimization that yields a response function that closely resembles
experimental measurements. Our work suggests that the bacterial chemotactic
response function can be derived from simple behavioral considerations, and
sheds light on how the response function contributes to chemotactic
performance.

Cell Behavior;Statistical Mechanics;Populations and Evolution