ABSTRACT
This chapter considers the robustness of a remarkable system called bacterial chemotaxis that allows bacteria to navigate. Bacterial chemotaxis is so well characterized on the level of molecules and behavior that it was a testing ground for important ideas in systems biology, including robustness. It describes the biology of bacterial chemotaxis, and models and experiments that demonstrate how the computation performed by bifunctional protein circuit is made robust to changes in protein levels. Most bacterial species show chemotaxis, and some can sense and move toward stimuli such as light and even magnetic fields. Bacterial chemotaxis achieves remarkable performance despite the physical limitations faced by the bacteria. The basic features of chemotaxis can be described by a simple experiment. Bacterial chemotaxis shows exact adaptation: the tumbling frequency in the presence of attractant returns precisely to the same level as before attractant was added. The robust model for bacterial chemotaxis can supply an explanation for these chemotactic personalities of Escherichia coli cells.
