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Regulatory Control and the Costs and Benefits of Biochemical Noise

Figure 1

A Sketch of the Instantaneous Growth Rate λ of a Single Cell as a Function of the Concentration X of Component X.

If the average expression level Xs is close to the optimal expression level Xopt, biochemical noise will always decrease the growth rate. If, however, the average expression level deviates sufficiently from the optimal expression level (i.e. if ax>bx2 in Equation 11), then fluctuations can enhance the growth rate of the population, even when the growth rate λ of a single cell is linear in X, i.e. if b = 0. The reason is that fast growing cells dominate the population.

Figure 1