Comparison of electrocompetencies of some commonly used laboratory strains of Escherichia coli

During construction of genomic libraries from various bacteria, we experienced considerably different transformation effi ciencies among the strains of electrocompetent Escherichia coli cells and investigated the effect of type strain on effi ciency of transformation. Among the fi ve strains tested, Escherichia coli DH10B and TOP10 were found to be the most suitable strains for construction of genomic libraries in our laboratory. This study highlighted the fact that although these commercially available Escherichia coli strains are well characterized, they tend to differentiate and loose their transformation abilities. This may be due to the fact that the number of passages they have gone through affect their membrane structures and permeability. Therefore, every laboratory should test their strains for competency before they use them in their cloning studies.

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