Factors Affecting Transformation Ability of Competent Escherichia coli Cells

Abstract: A number of factors including strains， bacterium activation， growth status， transformation solutions， plasmid length and purity， freezing stabilizers and storage duration were evaluated for their effects on transformation ability of competent Escherichia coli cells. The results suggested that the highest transformation ability can be obtained when activated TG1 was cultured to an A₆₀₀ of 0.55， prepared with 100 mmol/L CaCl₂， and kept on ice for 6 h before transformation. When pUC19 was applied， the transformation efficiency for optimized protocol was found to be as high as between 2×10⁶-4×10⁷ cfu/mg DNA. The efficiency decreased when a plasmid with increased length or a plasmid sample with impurities was applied. As a stabilizer for frozen competent cells， 15% glycerol was found to be better than 7% DMSO， however， both of them inhibited transformation. Competent cells stored in glycerol retained desirable transformation efficiency for 2 months at -70 ℃

CSTR: 32200.14.cjcb.2004.04.0024