Protoplast transfection of Lactobacillus casei by phage PL-1 DNA.

Polyethylene glycol (PEG) mediated transfection of Lactobacillus casei ATCC 27092 protoplasts by phage PL-1 DNA was done. The protoplasts were obtained by treatment with purified PL-1 phage N-acetylmuramidase in the presence of citrate. Optimum conditions for transfection were 50% PEG 4,000, 15 micrograms protamine sulfate/ml, 0.15 M sucrose, and 10 mM MgSO4 in MR medium (pH 6.0). The extent of transfection was proportional to the amounts of DNA added, and the greatest efficiency of transfection after a 10-min incubation was about 3.3 x 10(5) PFU/micrograms DNA. The eclipse period of growth of progeny phages in the transfectants was 3 hr and the average burst size was 200.