Figure 3. Mutations exert independent effects upon enzyme expression but a mechanistic model of benefits and costs of enzymes is required to predict combined effects on fitness.

A) Expression levels (in mU) are well predicted by independent, multiplicative effects of each mutation on the FlhA and FghA enzymes. B) Using a kinetic model of catalysis and costs parameterized with data from the single mutants and inducible promoter constructs predicts the mutational combinations very well (R² = 0.98).