Optimization of induction conditions
For the optimization of IPTG concentration, after the culture was transferred to TBSB, IPTG with a final concentration of 0, 0.05, 0.1, 0.2, 0.4, 0.6, 0.8, and 1.0 mM was added to the culture medium. Then, MWP was kept at 25℃ and 220 rpm for 24 h.
For the optimization of the pre-induction period, three transformants were picked up for each strain and activated in MWP containing 2 mL LB medium and 50 mg/L kanamycin at 37 ℃, 220 rpm for 12 h. Then, the cultures were transferred to 2 mL fresh TBSB medium with a 10% (v/v) inoculation rate. 0.1 mM IPTG was added to the culture medium at 0, 1, 2, 3, and 4 h after inoculation, respectively. All MWPs were kept at 25℃, 220 rpm for 24 h.