Figure 4

Narrow distribution of mutational robustness R _μ for genotypes in V(n). The horizontal axis shows the mutational robustness R _μ and the vertical axis shows the frequency of genotypes with the corresponding value of R _μ in a random sample of 1000 genotypes viable in a) glucose, b) acetate and c) succinate environment with the viability constraint taken as having strictly positive biomass flux. d) The distribution of mutational robustness R _μ in 1000 random viable genotypes for the glucose environment with viability constraint taken as biomass flux at least as large as the in silico E. coli biomass flux [24]. In all subfigures, we have shown the normal distribution with sampled mean and theoretically predicted variance as a dashed black curve (see text for details). The figures show that there is very little variation in R _μ across random viable genotypes and the normal distribution agrees well with the sampled distribution. In all cases, the number n of reactions is equal to that in E. coli (n = 831).