Verification of recombinants after positive or negative selection
After spread onto corresponding selective agar plates, colony PCR was used for identification of positive recombinants. A general principle for designing diagnostic PCR primer is: one primer is surrounding the target region and the other is inside the donor DNA. Two paired primers surrounding each side of the target region respectively were also designed in some case to display the different size of target DNA between the original strains and positive recombinants.