Fig. 4

Fermentation parameter optimization. a Violacein production and biomass of 21850 (pEC-vioABCDE) with 1, 3, 5 and 7 % corn steep liquor supplementation in fermentation. 1 % CaCO₃ was added to 5 % steep liquor culture for further improvement. b Temperature optimization for 21850 (pEC-J-vio1) of the second-phase of fermentation. violacein and biomass at 20, 25, 30, 37 °C was illustrated. c IPTG concentration was optimized for 21850 (pEC-J-vio1) fermentation at 0.25, 0.5, 1.0 mM for 21850 (pEC-J-vio1). Corresponding violacein production and biomass was illustrated. d Optimization of induction time of 21850 (pEC-C-vio1) for violacein production. After inoculation, 0.5 mM IPTG was added at 6, 12, 18, 24, 30 h and then fermentation was performed at 20 °C for 72 h with addition of IPTG. Experiments were carried out in triplicate