Electrotransformation of Escherichia coli

Abstract

Electrotransformation of selected bacterial species is a common laboratory technique that allows researchers to introduce macromolecules like DNA into a wide variety of gram-negative and -positive bacterial species. The discharge of a short-duration, high-voltage pulse through a dense bacterial cell suspension (108 to 109 cells/ml) temporarily permeabilizes some cells and allows entry of DNA. In addition, some cells are usually killed during the high-voltage discharge. This is dependent on the applied voltage, capacitance setting, duration of the discharge, bacterial species, and cell size. It is not known if DNA entry is a single-step event or if the DNA is electrophoresed into the cells. Transformation frequencies approaching 100% can be achieved for certain strains of Escherichia coli (gram-negative organism). However, most gram-positive strains are electrotransformed at lower frequencies and efficiencies. Moreover, some gram-positive bacterial strains have not been electrotransformed even though a wide variety of electrotransformation conditions have been tested. Nevertheless, electrotransformation is a simple, rapid, and inexpensive method for introducing DNA into intact bacterial cells. This offers a unique advantage in bacterial strains when other DNA introduction techniques have failed to succeed. This review will examine both fundamental and applied aspects of electrotransformation of bacteria. Presently, electroporation and electrotransformation are often used interchangeably. However, electrotransformation is probably the more correct term and will be the more commonly used term in the future.