Abstract: Single inactivated protoplast fusion technique was used for the fusion of Lactobacillus delbrueckii FQ with Lactococcus lactis FL. The protoplast formation, regeneration and fusion conditions were examined in this study. Results showed that the optimal enzymolysis conditions for L. delbrueckii FQ were ultrasound treatment for 90 min at 37 ℃ in the presence of 10μg/mL mutanolysin and 1 mg/mL lysozyme. Under these conditions, the protoplast regeneration rate reached 6.36%. The protoplast formation rate of L. lactis FL was up to 99.97% after 90 min of treatment with 10 mg/mL lysozyme in the presence of 1 mg/mL glycine. L. lactis FL protoplasts showed an inactivated rate of 96.89% after 120 min of exposure to 65 ℃. The fusion rate between Lactobacillus delbrueckii FQ and Lactococcus lactis FL reached 2.72 × 10-6 after 5 min of infusion at pH 6.5 in the presence of 400 g/L PEG 6000 (included 0.02 mol/L MgCl2 and 0.01 mol/L CaCl2).

Key words: single inactivation, Lactobacillus delbrueckii, Lactococcus lactis, protoplast fusion