Fig. 3

Performance of the engineered promoters in the presence of vanillin. Time after the addition of vanillin (inducer): a 0 h; b 4 h; c 8 h; and d 12 h. Gene expression is more prominent after 8 or 12 h after induction. The fluorescence of E. coli strains expressing mCherry under the native promoter P_emrR and the engineered promoters P_vtac, P_vtrc, and P_vtic were monitored using a fluorescence plate reader and normalized based on the cell density—OD₆₀₀. The cells were grown in an M9 salt medium containing 25 mg l⁻¹ chloramphenicol, 20 g l⁻¹ glucose and 5 g l⁻¹ yeast extract at 30 °C, and a 3 mm shaking amplitude. P_emrR, red squares; P_vtac, orange triangles; P_vtrc, grey circles; P_vtic, blue diamonds. Each data represent the average of three biological replicates and the error bars represent s.d. The standard deviations between the biological replicates were too small for the error bars to be visible