Affecting Factors of Forming Competent Cells of Escherichia coli JM109

Objective:Analyzing the affecting factors of forming competent cells of Escherichia coli JM109 to increase transformation efficiency.Methods: A series of Escherichia coli JM109 competent cells were produced in different conditions,including growth status,transformation solutions,storing time at 4℃,activating time at 42℃,plasmid length.Different effects on transformation ability of competent Escherichia coli JM109 were evaluated.Result: The highest transformation ability was obtained when the activated cells was cultured to an OD(600) 0.82,then prepared with 20mmol/L MgCl2 and 80 mmol/L CaCl2,kept at 4℃ between 12h to 24h,hot shocked at 42℃ for 60s.The transformation efficiency for optimized protocol was found to be as high as between 9.8×106 to 1.2×107cfu/μg DNA(pUC19).The lower efficiency was,the longer the length of the plasmid was.Conclusion: The formation of the competent cells was concerned with growth status,some metal ions and organic solutions.The physiologic change could take place in the process of forming competent cells.