Fig. 4

Performance of the engineered promoters in the presence of a vanillic acid and b coumaric acid. 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 after 24 h of induction 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 bars; P_vtac, orange bars; P_vtrc, grey bars; P_vtic, blue bars. Each data represent the average of three biological replicates and the error bars represent s.d