Abstract 

Bacterial motility is among the quantitatively best-understood biological behaviors, at it has long served as a model of how physics can help to understand limits to bacterial ability to move and follow chemical gradients in the environment (chemotaxis). Much less explored is the question of what determines the investment of finite resources, biosynthesis and energy, into bacterial motile behavior under different conditions. Using example of Escherichia coli, we demonstrate that knowing physical limitations on bacterial motility, fitness tradeoffs between motility and growth, and anticipated benefits of motility can be sufficient to quantitatively explain natural regulation of motility gene expression. Understanding such evolutionary optimized investment strategies could help to rationalize and predict many regulatory patterns observed in biology.