Vibration and glycerol-mediated plasmid DNA transformation for Escherichia coli

Abstract

Escherichia coli transformation is an essential step in many molecular biology experiments. Despite earlier advances in the field, many studies including shotgun cloning still require more efficient transformation protocols. Chemical transformation has been the most popular method, in which competent cells are transformed following a brief period of heat shock. Here, we report a novel protocol with higher efficiency, in which competent E. coli cells (treated with CaCl2 ) grown in media containing glycerol experience a gentle vibration. Three E. coli strains DH5α, Jm107 and BL21 (DE3) and three plasmids pGEM-T, pET-28a and pCAMBIA with different sizes (3000, 5369 and 8428 bp, respectively) were used to test the protocol. The results indicated a significant increase in number of transformed colonies compared with heat-shock method. Our findings also demonstrated the favourable impacts of glycerol on transformation of E. coli.

Keywords: CaCl2; Escherichia coli; cloning; heat shock; transformation.