• Microbiology and Biotechnology Letters
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• v.14 no.3
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• pp.265-270
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• 1986

The best conditions for the protoplast fusion of Lactobacillus casei have been searched for in this study. Antibiotic resistance was used as the selective marker for enumerating and selecting the recombinants. Antibiotic resistant mutants were isolated after treating cells with N-methyl-N'-nitro-N'-nitrosoguanidine. High frequency fusion of protoplasts of L. casei strains were obtained in the presence of 40% (wt/vol) polyethylene glycol 4,000 after 1 min at 3$0^{\circ}C$ at around neutral pH. Spontaneous mutations of drug-resistance of L. casei were two or three orders lower than the recombination frequency. Recombination frequencies were about 10$^{-4}$ per parent cells employed.