FIG 3 .

The vio2ta16 native promoter is not efficiently activated in E. coli. (A) Schematic illustration of the pET28a-vio2ta16 construct. The native vio2ta16 promoter was replaced by transfer of the biosynthetic operon into expression vector pET28a, placing the pathway under the direct control of the T7 promoter. (B) Heterologous violacein production from E. coli BL21(DE3) harboring pET28a-vio2ta16. Cultures were grown to an OD₆₀₀ of 0.5 to 0.6 at 37°C before induction with different concentrations of IPTG as shown. Following induction, liquid cultures were incubated for 24 h with shaking at 18 or 30°C before extraction and violacein quantification by HPLC. The data plotted are the mean ± standard error from two independent experiments (total n = 6).