Bio-Rad MicroPulser™ Electroporator - Manual (Page 11)

transformants recovered is the product of the transformation frequency and the number of
cells present, the transformation efficiency (transformants/µg DNA) increases with cell
concentration over the range of 10
9 to at least 3 x 10 10 cells/ml. Therefore, to obtain a high
transformation frequency, use high DNA concentration. To obtain high transformation
efficiency, use high cell concentration (and low DNA concentration to avoid
cotransformations). In each case, a small sample volume (20–50 µl) allows economical use
of DNA and cells (see Dower et al., 1988, for a detailed discussion of these factors).
3.3 Electroporation Media
The MicroPulser is designed for use with samples in high resistance media (>600 ohms).
For this reason, when preparing electrocompetent cells, it is important to wash cells
thoroughly to remove all traces of growth media. Failure to thoroughly remove the growth
media from the cells may result in the sample arcing during electroporation. Cells should be
washed at least three times with water or with non-ionic solutions, such as glucose, glycerol,
sucrose, sorbitol, or polyethylene glycol. For many microorganisms, glycerol is a convenient
electroporation medium, since it is recommended as a cryoprotectant for storage of cell cultures.
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