Optimized transformation by electroporation ofLactobacillus plantarum strains with plasmid vectors

Summary Whole cell transformation ofLactobacillus plantarum CCM 1904 by electroporation was optimized. Pulse duration and electric field strength were shown to be important parameters: the optimum conditions were 12.5 kV/cm, a time-constant of 10 ms for an exponential decay waveform and 6.7 kV/cm applied during 2.5 ms for a square waveform. Transformation efficiency was increased if cells were cultivated on medium containing sorbitol and harvested during their early exponential growth phase: 8 × 10^–4 transformants/g pGK12 DNA per viable cell were obtained, with a survival rate of 10%–30% Cryotreatment by several freeze-and-thaw cycles decreased transformant yields. Transformation efficiency with different plasmids was studied and plasmid pGK12 was found to transformL. plantarum the most efficiently. Transformation by electroporation ofL. plantarum is strain dependent. The best results were obtained withL. plantarum NCIB 7220, giving 5 × 10⁶ transformants/gmg plasmid pGK12 DNA.