Study of Transformation Methods for Chemically Competent E. coli Cells

Abstract

Bacterial transformation is the ability of bacteria to uptake foreign DNA. High transformation efficiencies (TEs) are important in various molecular cloning processes, DNA library construction and transformation of large plasmids. Therefore, common laboratory strains are made competent by treating their membranes to enhance plasmid uptake. Transformation and storage solution (TSS) is a buffer for making common laboratory E. coli competent cells. (Chung et al., 1989). Two recent studies have reported one to two-log improved TEs (Yang, Liu, et al., 2022; Yang, Yu, et al., 2022), using slightly modified transformation buffers (TSS or TSS-HI) and methods (KCM or Heat shock). Here, we intend to reproduce these two improved methods. We prepared chemically competent E. coli cells using TSS or TSS-HI buffers. The competent cells were transformed using KCM, heat shock, or heat shock + KCM methods. Results revealed that E. coli strains washed with the modified TSS and TSS-HI buffers and transformed via different methods did not exhibit any significant improvement or difference in the transformation efficiency. However, the modified protocols produce competent cells suitable for quick transformation, eliminating the need for incubation on ice (usually 30 minutes) or recovery (about 1 hour). Our findings refute the reported modifications' effectiveness, reliability, and reproducibility in improving TEs.