Electrotransformation of the stable L-form ofProteus mirabilis

Abstract

To improve the transformability of stable protoplast type L‐forms of Proteus mirabilis for recombinant plasmid DNA, conditions for efficient electrotransformation were explored. Exposing cells from the exponential phase of growth at a density of 6−8 × 109/ml in electrotransformation buffer having a conductivity of 1.4 mS/cm to a field strength of 6.5 kV/cm for a mean pulse duration time of 1.2 ms reproducibly yielded transformation efficiencies in the order of 5 × 104 transformants per μg of DNA. Compared to the polyethylene glycol method for transformation, electrotransformation appeared to be the method of choice for introduction of plasmid DNA into L‐form cells.