• Microbiology and Biotechnology Letters
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• v.20 no.1
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• pp.6-13
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• 1992

- Protoplast fusion between lincomycin resistant Lactobacillus casei KCTC 1121 and rifarnpicin resistant Lactobacillus delbrueckii JK-414 was attempted to obtain the improved strains. Protoplasts of L. casei and L. delbrueckii were produced by mutanolysin digestion at $42^{\circ}C$ for 15 min. L. casei cells were converted to protoplasts by treating with 5 $\mu g$ / m l of mutanolysin in 20 mM HEPES buffer (pH 7.0) containing 0.75 M sucrose at the middle logarithmic growth phase. In case of L. delbrueckii 1.0 M sucrose was used osmotic stabilizer. Regeneration of protoplast in both strains was efficiently accomplished on the regeneration medium containing 10% sucrose, 6 mM $MgC1_2, 6 mM CaC1_2$, and 2.5% gelatin. Protoplast fusion between L. casei and L. delbrueckii was carried out in the presence of 40% of PEG 4,000. The frequency of protoplast fusion was found to be about $3.2\times 10^4$. Acid production of L. casei was better than that of L. delbrueckii. Among fusants, F23 and F35 exhibited excellent lactic acid production. F23 and F24 exhibited the improved proteolysis compared to that of the parent strains and they had twice as much as DNA content of the parents.