Study on the Preparation of the Competent Cells of Escherichia coli

Objective: In order to get a method of competent cells preparation with well repeatability and high transformation efficiency,different growth phase of Escherichia coli was used to transform and compared their transformation efficiency.Methods: Draw the growth curve of Escherichia coli,choose the correct time to make competent cells,plasmid DNA was extracted using alkaline lysis method,transformed plasmid DNA into host cells using CaCl_2 method,compared the transformation ratio of different growth phase of Escherichia coli. Results: The transformation efficiency of E.coli was the highest in 0.39 and 0.55 of the OD_(600nm),and it showed that the competent cells could have better transformation efficiency when Escherichia coli grew up OD_(600nm) to 0.28-0.55.Conclusion: Because the preparation of the competent cells needed not any chemical reagents and anabiosis culture,the method of preparation of the competent cells of Escherichia coli was simple,repeatable and economical.