Transformation in Escherichia coli



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The maximum peak of transformation in Escherichia coli appears at the transition from the lag phase to the exponential phase of the growth curve. A minor peak occurs in the transition from exponential to stationary phase. These peaks of transformation were correlated with methylene blue adsorption. The effect of the growth media on transformation was studied. Highest percent of transformation was obtained in glucose minimal, next was succinate minimal, followed by brain heart infusion. However, the best transformation was obtained in a glucose-succinate minimal, (glucose limiting) medium. The highest percent transformation occurred during the shift from glucose as sole carbon source to succinate as sole carbon source. Increased permeability of the cells obtained by short treatment with phenethyl alcohol, increased the percent transformation. Substituting BaCl2, MgCl2, or SrCl2 in place of CaCl2 gave little or no transformation throughout the growth curve. Transformation was also monitored using a synchronous culture, through two cell divisions.