*4.7. Genetic Transformation Efficiency of β*−*lactamase Mutants*

To calculate the electroporation efficiencies of the β−lactamase mutants, a 3−kb shuttle plasmid pEZ15A and a 10−kb shuttle plasmid pE39−MVA were prepared from *E. coli* DH5α and introduced into ZM4, ZM4∆0103, and ZM4∆Ars. Electroporation efficiency was presented by the colony forming units (CFUs) on selective plates when 50 µg plasmid DNA was introduced and 100 µL recovery culture was plated. The calculating formula is described below:

$$\text{CFU} / \mu \text{g}^{-1} \text{ DNA} = (\text{Cp} / \text{Tp}) \times (\text{Vt} / \text{Vp}) \text{yr}$$

where Cp is the colony number counted on selective plates; Tp is the total amount of plasmid DNA (µg) used here; Vt is the total transformation volume (µL); Vp is the volume (µL) plated.
