Induction of competency and comparison of transformation efficiency in Escherichia coli using different salt solutions - Cations

Author : Gunasagaran Karuna, Natesan Munuswamy

Escherichia coli (DH5α) was treated with different salt solutions to attain a physiological state of competence for transformation. Salts were dissolved in water to make ionic solutions containing cations of different valencies. Ionic solutions of sodium chloride (NaCl) monovalent (Na+), magnesium sulphate (MgSO4) divalent (Mg2+), aluminium chloride (AlCl3) trivalent (Al3+) and conventionally used Calcium chloride (CaCl2) divalent (Ca2+) cations were used to induce competency. Competent cells prepared were stored in 50 % glycerol at 20 C and the transformation efficiency was compared using a plasmid vector pUC19. Efficiency of cations inducing competency with higher transformation rates was seen in the order Na+>Ca2+>Mg2+>Al3+ for freshly prepared cells; later it was Ca2+>Na+>Mg2+>Al3+. Cells under storage showed transformation efficiency of 105-106 CFU/g DNA for 5 weeks. This result concludes competency could be induced using salt solutions of different cations with difference only in their transformation efficiency. Chemical induction method being a conventional method other different salts could be used for better transformation efficiency in other organisms.

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