Summary
Transformation of bacteria with plasmids is widely used for molecular cloning of the genes and other purposes. To enable naked DNA to enter the cells, either bacteria are made “competent” by treatment with calcium chloride, or electroporation, which requires expensive equipment, is used. As an alternative to these methods, we have investigated cationic lipids and zwitterionic surfactants for their ability to carry plasmids into bacterial cells. For transformation studies, overnight Escherichia coli cultures were suspended in calcium chloride solution; naked or complexed plasmids with lipids and surfactants were mixed with prepared bacteria and incubated either on ice or at 37°C for various time periods. After washing the samples with phosphate buffer (pH 7.4), Luria Bertani (LB) medium or 5% (w/v) bovine serum albumin (BSA) solutions, pellets were inoculated on LB agar. Among the factors evaluated for transformation of bacteria, the best results were obtained with the complex DNA-cationic lipid-zwitterionic surfactant, incubation on ice for one hour, and treatment with BSA wash solution. Complexing plasmids with lipids and surfactants and washing with BSA solution may promise easy and rapid means to transform various types of bacteria.

Key Words :
Bacterial transformation, cationic lipids, Escherichia coli, plasmid DNA, zwitterionic surfactants.