The dynamics in the bacterial chemosensory arrays

Bacterial chemoreceptors form two-dimensional sensory arrays on the cell membrane. These sensory arrays, which contain thousands of molecules, detect chemical changes in the environment of the bacterial cell and accordingly control its swimming behaviour, allowing these bacteria to track chemical gradients. It was recently demonstrated that stimulus, by ligand binding, alters the physical organization of these arrays, with dynamics that follow an apparent logarithmic time dependence. Such non-exponential dynamics is often observed in glass-like systems in which the internal dynamics slow down exponentially as the system approaches its equilibrium state. In a few of these "glassy" systems it was also demonstrated that after altering the equilibrium state of the system for a certain time t_w the ensuing relaxation scales with t_w. Here, we examined the relaxation of the receptor arrays in the bacterium E. coli after a perturbation by ligand binding for varying periods of times. We find that changing the time t_w, during which the stimulus was present, affects mostly the deviation of the receptor arrays from equilibrium, but the dynamics of the relaxation seem to be independent of t_w. A possible interpretation is discussed.