Effects of DNA Topology on Transformation Efficiency of Bacillus subtilisISW1214 by Electroporation

We report an investigation of electrotransformation by three different topological isomers, circular supercoiled (sc DNA), circular relaxed (cr DNA), and linearized (In DNA) forms of the plasmids pUB110 (4.5 kbp) and pBDR331T (12.6 kbp), of a Gram-positive bacterium, Bacillus subtilisISW1214. Treatment of the sc DNA with calf thymus topoisomerase I removed the superhelicity and the DNA assumed the relaxed circular form. Treatment of sc DNA with restriction endonuclease linearized the DNA. The transformation with the sc DNA of pUB110 resulted in the maximum efficiency of (2.6±0.6) × 105transformants per μg DNA higher than that ((2.0±0.3) × 104transformants per μg DNA) for the cr DNA, using the DNA concentration of 20 μg/ml at an electric field strength of 7kV/cm and a capacitance of 10 μF with a single decayed pulse. The transformation efficiency (TE) for the In DNA was zero. The variations of TE for different topological forms of DNA reflected their relative stability in the host cells. The molecular efficiency (ME, transformants per molecule) for sc DNA was nearly one order of magnitude greater for the lower molecular size of pUB110 DNA than that for the higher molecular size of pBDR331T DNA.