Adaptation Dynamics in Densely Clustered Chemoreceptors
Figure 3
Spontaneous output of the bacterial chemotaxis system.
Results are from stochastic simulations of a chemotaxis model M1 with a hexagonal receptor lattice and explicit enzyme tethering and the model B1 with no tethering or lattice structure. (A) We sampled representative cells from a population in which the ratio CheR/CheB/chemoreceptors is maintained but the overall expression level varies. Stochastic simulation of model M1 (black) predicts that some cells in this population will exhibit especially large fluctuations σa/a0∼10%. The magnitude of fluctuations increases sharply as the level of protein expression decreases. Noise levels in M1 are significantly larger than in B1 (gray) at all expression levels. The horizontal axis is normalized by the most common expression level. (B) The variance σaa of fluctuations in receptor activity is shown as CheR is varied while all other proteins are expressed at their mean levels. The variance σaa is significantly greater in M1 (black, diamonds) than in B1 (gray, circles). The model M1 produces exceeding 7% of the mean level (black, inset), while noise in B1 remains less than ∼3% (gray, inset). The noise was increased in B2 by increasing the enzyme-receptor affinities tenfold (light gray) relative to B1. (C) M1 and the (black, diamonds) and B1 (gray, circles) also exhibit similar dependence of the mean receptor activity at steady state a0 on CheR count. The model B2 with higher enzyme-receptor affinities exhibits highly ultrasensitive dependence on the CheR count (light gray).