IPTG measured in the supernatant of cultures of strains with or without lactose permease, as a function of cell density. Measured IPTG in supernatants of MG1655-Z1 (lacY+) cultured broth conditions as a function of cell density, expressed as OD600 (A). Measured IPTG in supernatants of DB3.1 and MC1061 (lacY-) cultured broth conditions in LB pH 7.0 at 37°C over time (B). Growth of DB3.1 and MC1061, expressed as OD600, in a representative experiment performed in LB pH 7.0 at 37°C (C). In all the panels, circles represent data points, with colours specified in the legends, and error bars represent the 95% confidence intervals of the average.