2.6 SDS-PAGE analysis and protein quantitation
After 24 h cultivation, 10 OD600 of cells harboring PCP vaccine proteins were harvested by centrifugation at 12,000g, 4 °C for 10 min. Cells were washed and resuspended with 1 mL PBS, and then disrupted by sonication on ice. After sonication, the lysates were centrifuged at 12,000g for 15 min and the supernatants were collected for 12% (w/v) SDS-PAGE analysis. The concentration of the target protein band was determined by measuring and comparing its strength with that of standard bovine serum albumin (BSA) at a known concentration loaded in the same gel (Image J software).