Cost-Benefit Model for Interactions between MAR inducers and Antibiotics. a. The combined growth cost of two drugs (S and A) is assumed to be Bliss independent, as long as the effective concentration of one drug is reduced by the presence of the second drug. Thus, the combined cost of both drugs is approximately equal to the sum of effective growth costs, f and g, for each individual drug. The reduction of each drug's growth cost depends on the concentration of the other drug, which in turn dictates the growth benefit provided. b. mar promoter activity, defined as the steady state time-averaged Fluorescence/OD times relative growth rate, increases as a function of salicylate concentration. Error bars are +/− one estimated standard deviation. Inset: mar fluorescence concentration (YFP fluorescence/optical density) time series for concentrations of salicylate ranging from 0 mM (purple) to 6 mM (blue). Data points are means over two replicates. Promoter activity is estimated by averaging fluorescence concentration in the steady state and multiplying by relative growth rate.