Electrotransfection of Propionibacterium freudenreichii TL 110

The first highly efficient protocol is described for the electrotransfection of Propionibacterium freudenreichii with DNA phage. The transfection efficiency is 7 times 10⁵ transfectants per μg of DNA under optimal conditions. Optimized parameters included the field strength (12.5 kV, 200 Ohms, 25 μF), phage DNA concentration (1 μg ml^-1) and cell density (1.5 times 10¹⁰ cells ml^-1). Growth in the presence of glycine and harvesting of cells during the early exponential growth phase increased the transfection efficiency. This electrotransfection protocol is of importance for the genetic improvement of dairy propionibacteria.