TRANSFORMATION OF STREPTOCOCCUS-BOVIS PROTOPLASTS BY PLASMID DNA

The transformation and subsequent regeneration of ruminal strain Strep tococcus bovis AO24/85 protoplasts by plasmid DNA was studied. The bes t stabilizer for regeneration of protoplasted cells was 5% sucrose in the regeneration medium and in the agar plates. Optimal concentration of polyethylene glycol 6000 in the transformation medium was 25% for b oth plasmids tested. Addition of Ca2+ and Mg2+ ions (2.5 mmol l(-1)) t o the transformation medium increased the proportion of regenerated ce lls. Transformation frequencies were 3 x 10(3) transformants per mu g of pNZ12 and 2.4 x 10(2) per mu g of pJK108, respectively.