Figure 2

Growth rate g(I, P) as a function of IPTG and Pgal, interpolated and smoothened from Figure 1. The decoupling of inducer and carbon source is evident: addition of Pgal when not expressing lac operon genes (low IPTG concentration) will not result in growth rate increases, and addition of IPTG without Pgal will lower the growth due to an expression cost. The ridge in the landscape is caused by anti-induction of the lac repressor by Pgal, when present at a high concentration (see Additional file 1). For low Pgal concentrations we used a functional relation for the cost of expression fitted to the data (Additional file 1).