TRANSFORMATION OF LACTOBACILLUS STRAINS USED IN MEAT AND VEGETABLE FERMENTATIONS

For transformation of Lactobacillus plantarum and Lactobacillus sake strains of meat and vegetable origin, electroporation using the electroporation solutions 952 mM sucrose with 3-5 mM MgCl2 or 30% polyethylene glycol (PEG 1500) was found to be efficient. The highest transformation efficiencies for all the meat strains and most of the vegetable strains were obtained using PEG 1500. Although the transformation efficiencies varied, the strains tested showed essentially the same response pattern to different electrical pulses, as illustrated by response surface plots. For screening purposes a setting of 1-5 kV and 400 ohm pulse control resistance is recommended. For optimization of transformation efficiency for specific strains, selected combinations of voltage and pulse control resistance along the optimum shown in the plots can be used. Transformation efficiencies can be further improved by using medium shift from MRS without dextrose to MRS, and by including a magnesium solution in the washing procedure. The combined effect of these pre-treatments has raised the transformation frequency of previously low transforming strains with a factor of 10(3), giving transformation efficiencies sufficient for most practical applications.