Charge dependent electroporation of Escherichia coli C600

•Electroporation of E. coli depends only indirectly on the current density.•Applying a square wave generator an extraordinary behavior of the current pulses could be observed.•Not only a direct current but also a dielectric coupled current in form of a displacement current appears.

Experiments performed with a voltage generator giving one pulse with an exponential decay showed that the transformation efficiency in dependence on the current density had a clear shift of the transformation maximum according to the conductivity of the bacteria suspension for Escherichia coli C600 as well as for Bacillus subtilis 168. For higher conductivities, higher current densities are needed to reach the transformation maximum.In this study a square wave generator was applied. It was explicitly shown, that electroporation of E. coli depends only indirectly on the current density. In fact, the key parameter is the amount of charges applied to the bacteria. During the measurements with the square wave generator an extraordinary behavior of the current pulses could be observed which leads to the following assumptions: During the electroporation process there is not only a direct current but also a dielectric coupled current in form of a displacement current taking place within the cuvette.