Optimization of expression vector
PCP vaccine protein genes were cloned into different expression vectors. To compare the expression performance of these vectors, 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, and 1 mM IPTG was directly added after inoculation. After 24 h of induction, the cells were collected and disrupted for SDS-PAGE analysis.