Experimentally measured and predicted fitness of PF cell populations after incorporating cellular memory at various combinations of ATc and Zeocin.

<p>(A) Overall population-level fitness reduction as a function of increasing Zeocin concentrations at 0 ng/ml ATc, reflecting the toxic effect of the antibiotic. (B) Overall population-level fitness reduction as a function of increasing ATc concentrations at 0 mg/ml Zeocin due to various costs related to inducer-bound rtTA. (C) Predicted overall population-level fitness landscape for PF cells as a function of extracellular ATc and Zeocin. The fitness landscape is calculated from the 2-state cell model with division rates and switching rates inferred from cellular memory and the marginal fitness functions <i>γ</i>₁(<i>F</i>,<i>Z</i>) (green edge) and <i>γ</i>₂(<i>F</i>,<i>C</i>) (purple edge) shown in panels (A) and (B), respectively (D) Experimental measurements (black dots) and computational predictions either incorporating (red line) or omitting (blue line) cellular memory of overall fitness of PF cell populations at different concentrations of ATc and Zeocin = 2 mg/ml. The incorporation of cellular memory improves the agreement between the predictions and experiment. (E) Computational predictions based on the gene expression distributions assuming fast switching (blue circles) explained barely <0.1% of overall cell population fitness, while predictions based on fitness landscape and memory (red circles) explained 98.5% of overall cell population fitness. (F) Experimental yEGFP::ZeoR histograms at the “sweet spot” of drug resistance of 1 ng/ml ATc before selection (Zeocin = 0 mg/ml, green line) and after selection (Zeocin = 2 mg/ml, red line). Note the drastic difference between these two histograms with PF cells changing from almost 100% low expressors to nearly 100% high expressors following selection.