OPTIMIZED TRANSFORMATION BY ELECTROPORATION OF LACTOBACILLUS-PLANTARUM STRAINS WITH PLASMID VECTORS

Whole cell transformation of Lactobacillus 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/μg 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 transform L. plantarum the most efficiently. Transformation by electroporation of L. plantarum is strain dependent. The best results were obtained with L. plantarum NCIB 7220, giving 5 × 106 transformants/gmg plasmid pGK12 DNA. © 1990 Springer-Verlag.