Objective: To establish the methodology of plasmid for gene knock-out in Mycobacterium BCG.
Methods: We designed two pairs of primers for amplification of MDP1 gene and inserted two fragments into pKO plasmid, and then the recombinant plasmid for MDP1 gene knock-out was obtained, and named pKO-MDP1. Gene exchange took place within the genome of BCG after pKO-MDP1 plasmid was transformed into Mycobacterium BCG. The strain of Mycobacterium BCG with MDP1 gene knock-out was selected, and the curve of growth rate was studied.
Results: The target strain was that of the positive strain by two step PCR and one step sucrose counter selection, without growth in culture media with hygomycin. The value of A(600) per 12 hours was detected for sixteen days. A "S" shaped growth curve was detected. However, there was no significant difference in the growth rates between the wild type Mycobacterium BCG strain and the gene knock-out Mycobacterium BCG strain.
Conclusions: The plasmid of pKO was a useful tool for gene knock-out in Mycobacteria. MDP1 maybe one of the factors influencing the growth rate, but it was not the only one.