CTAB-mediated, single-step preparation of competent Escherichia coli, Bifidobacterium sp. and Kluyveromyces lactis cells

• We developed a simple and rapid procedure for the preparation of competent E. coli, Bifidobacterium sp., and K. lactis.
• CTAB permits efficient uptake of plasmid, as well as ligation reaction products.
• The equal transformation efficiencies were observed with cells harvested at late exponential and stationary phases.
• CTAB treated cells are used for transformation by heat shock, electroporation, etc.

An efficient and reproducible method for transformation depends on the competency of the organism. We have developed a simple method for the preparation of competent Escherichia coli, Kluyveromyces lactis, and Bifidobacterium sp. by using a buffer containing cetyl trimethyl ammonium bromide (CTAB) and permits efficient uptake of plasmid DNA and ligation-reaction products. Cells are harvested, washed, mixed with 1–10 μg/ml CTAB, incubated, and followed by a buffer wash. For long-term storage of competent cells, bacteria may be frozen in 10% glycerol without the addition of other components. The transformation process is very simple; plasmid DNA and the cells are mixed and incubated for 5–60 min at 4 °C; no heat pulse is required, and the duration of incubation at 4 °C is not crucial.