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.