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

Abstract

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/µg 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.