Mutagenesis and Protoplast Fusion for Enhanced Bacteriocins Production

Background and Objective: Induced mutagenesis is widely used to produce novel mutants with improved productivities. Ethyl methane-sulfonate-induced mutagenesis followed by intergeneric protoplast fusion were used to develop lactic acid bacterial strains with high antimicrobial activities. Materials and Methods: The antagonistic activities of seven LAB strains were assessed against seven indicator microorganisms using well diffusion assay. The highest two producers were subjected to ethyl methane-sulfonate mutagenesis followed by intergeneric protoplast fusion. Selection of the mutants and the fusants from the suggested fusion cross was based on the responses to different antibiotics. Results and Conclusion: Lactococcus lactis subsp. lactis and Bifidobacterium longum showed the highest antimicrobial activities against most of the indicator microorganisms. Such activities were achieved at pH 2.0 and dramatically decreased by increasing the pH level. Ethyl methane-sulfonate-induced mutagenesis resulted in thirty mutants, four of which exhibited higher activities than their wild type parental strains (two for each parent). In an attempt to increase such activity, intergeneric protoplast fusions between LM 13 (resulting from Lactococcus lactis subsp. lactis) and BM 4 (resulting from Bifidobacterium longum) mutants were carried out. Twelve fusants were obtained. Interestingly, one fusant (F1) showed an increase in antimicrobial activity, compared to its parental strains. An increased range of 58.1 to 345.7% compared to the parental strain Lactococcus lactis subsp. lactis and a range of 51.5 to 168.5% for the second parental strain were noticed. The LM 13, LM 6, BM 4 and BM 12 mutants and the F1 fusant can be used in the preservation of food products.