Transformation of Escherichia coli by Electroporation

Preparing electrocompetent bacteria is considerably easier than preparing cells for transformation by chemical methods. Bacteria are simply grown to mid-log phase, chilled, centrifuged, washed extensively with ice-cold buffer or H₂O to reduce the ionic strength of the cell suspension, and then suspended in an ice-cold buffer containing 10% glycerol. DNA may be introduced immediately into the bacteria by exposing them to a short high-voltage electrical discharge. Alternatively, the cell suspension may be snap-frozen and stored at -70°C for up to 6 mo before electroporation, without loss of transforming efficiency.