Resuspend the pellet in 1 L ice-cold H 2 O. Centrifuge as above. Resuspend in 0.5 L ice-cold H 2 O, and centrifuge as above. Cells are good for about 6 months. Thaw bacterial cells at room temperature and then place them on ice. Place sterile cuvettes and the white cuvette chamber slide on ice.
Temperature is important because the probability of arcing increases with temperature.
This may be increased to about 1 ng if low yields are obtained. Incubate on ice for 30-60 seconds. Do not use the 4mm cuvettes for bacteria. E. coli require a high field strength which is proportional to voltage x distance between the electrodes. Transfer the DNA-cell mixture to the bottom of a cold electroporation cuvette.