Figure 6. Simulating the effect of expression noise on fitness at different median expression levels.

(A) The linear function $DT=-40\times E+160$ relating the expression level of single cells to their doubling time used for the first set of simulations. (B) Relationship between mean expression (${\mu }_E$) and fitness at nine values of expression noise (noise strength: ${{\sigma }_E}^2/{\mu }_E$) ranging from 50% to 2000% using the linear function shown in (A). (C) Gaussian function $DT=-160\times \exp \left(-{\left(E-1\right)}^2/0.18\right)+240$ relating the expression level of single cells to their doubling time used in the second set of simulations. This function shows an optimal expression level at $E=1$, where doubling time is minimal (i.e., fastest growth rate). (D) Relationship between mean expression (${\mu }_E$) and fitness at 11 values of expression noise (noise strength: ${{\sigma }_E}^2/{\mu }_E$) ranging from 50% to 1400% using the Gaussian function shown in (C). (B,D) Error bars show 95% confidence intervals of mean fitness calculated from 100 replicate simulations for each combination of mean expression and expression noise values. Data are available in Figure 6—source data 1.

Figure 6—figure supplement 1. Simulating the effect of two different metrics of expression noise on fitness at different median expression levels.

Population fitness was simulated for median expression levels ${\mu }_E$ ranging from 10% to 100% and for: (A) the standard deviation of expression ${\sigma }_E$ ranging from 0.05 to 2 and the linear function $DT=-40\times E+160$ relating single cell expression to doubling time, (B) the coefficient of variation of expression ${\sigma }_E/{\mu }_E$ ranging from 0.05 to 2 and the linear function $DT=-40\times E+160$ relating single cell expression to doubling time, (C) the standard deviation of expression ${\sigma }_E$ ranging from 0.05 to 0.8 and the Gaussian function $DT=-160\times \exp \left(-{\left(E-1\right)}^2/0.18\right)+240$ relating single cell expression to doubling time, and (D) the coefficient of variation of expression ${\sigma }_E/{\mu }_E$ ranging from 0.05 to 1.4 and the Gaussian function $DT=-160\times \exp \left(-{\left(E-1\right)}^2/0.18\right)+240$ relating single cell expression to doubling time. (A–D) Error bars show 95% confidence intervals of mean fitness calculated from 100 replicate simulations for each combination of mean expression and expression noise.

Figure 6—figure supplement 2. Relationship between expression noise and fitness at different values of mean expression in simulations using a Gaussian function relating single cell expression to doubling time.

Three different noise metrics were used: (A) the noise strength ${{\sigma }_E}^2/{\mu }_E$, (B) the standard deviation ${\sigma }_E$, (C) the coefficient of variation ${\sigma }_E/{\mu }_E$. (A–C) Error bars show 95% confidence intervals of mean fitness calculated from 100 replicate simulations for each combination of mean expression and expression noise.