Bio-Rad MicroPulser™ Electroporator - Manual (Page 9)

The MicroPulser also includes a means to truncate the exponential decay pulse sooner
than the expected time constant as long as the voltage is greater than 600 V. When the pulse
is terminated by the MicroPulser, voltage is applied to the sample only for the specified time,
which may be between 1.0 and 4.0 msec. Figure 3 shows how this waveform differs from
the true exponential decay pulse.
Fig. 3. Truncation of an exponential decay pulse by the MicroPulser. The solid line shows the volt-
age applied to the cells as a function of time during a pulse terminated after 2.5 msec. The dashed line
shows the voltage that would normally be applied to the cells during a true exponential decay pulse.
Section 3
Factors Affecting Electroporation
The electrical conditions for the electroporation of microorganisms have been verified
through years of research (see Chang, et al., 1992, and Nickoloff, 1995, for overviews as well
as for protocols on electroporation of numerous species). For many microorganisms, opti-
mum electrotransformation occurs under electrical conditions relatively similar to those used
for E. coli and S. cerevisiae, two species that are most commonly used in research today. For
electroporation of E. coli, conditions reported as being used most often are 0.2 cm cuvettes con-
taining 40 µl of cells at a voltage of 2.5 kV and a time constant of ~5 msec. For
electroporation of S. cerevisiae, conditions reported as being used most often are 0.2 cm
cuvettes containing 40 µl of cells at a voltage of 1.5 kV and a time constant of ~5 msec. For
many bacterial species, including Salmonella, Pseudomonas, Helicobacter, Borrelia,
Streptococcus, Lactococcus, and Enterococcus, the conditions for electroporation are
identical to those used for E. coli. For many other bacterial species, altering the field strength
will often result in higher electrotransformation. A similar case is found with other species of
yeast.
The MicroPulser is designed to deliver precisely those pulse parameters needed for the
highest transformation efficiency of E. coli and S. cerevisiae. The time constant has been set
5
Voltage (V)
V
0
V
0
e
2.5 5
Time (msec)