The Effects of Ampicillin versus Tetracycline in the Selection of pBR322 Transformants

Escherichia coli DH5 α cells were transformed with pBR322 plasmids, which encode both ampicillin and tetracycline resistance genes. After 45- and 60-minute recovery periods, the transformed cells were plated on three types of selective plates, containing 1) ampicillin only, 2) tetracycline only, and 3) ampicillin plus tetracycline. It was found that tetracycline selection from these recovery periods resulted in a lower level of transformant survival than ampicillin selection. However, after the transformants were allowed to recover for several generations, their survival rates were similar on ampicillin plates and on tetracycline plates.