Control analysis of bacterial chemotaxis signaling

Bacteria such as Escherichia coli demonstrate the remarkable ability to migrate up gradients of attractants and down gradients of repellents in a rapid and sensitive fashion. They employ a temporal sensing strategy in which they estimate the concentration of ligand at different time points and continue moving in the same direction if the concentration is increasing in time, and randomly reorient if the concentration is decreasing in time. The key to success is accurate sensing of ligand levels in the presence of extracellular and intracellular disturbances. Research from a control theory perspective has begun to characterize the robustness of the bacterial chemotaxis signal transduction system to these perturbations. Modeling and theory can describe the optimal performance of such a sensor and how it can be achieved, thereby illuminating the design of the network. This chapter describes some basic principles of control theory relevant to the analysis of this sensing system, including sensitivity analysis, Bode plots, integral feedback control, and noise filters (i.e., Kalman filters).