Abstract:[Objective] Adopted a method of mixed induction, which can selected traits stable and growing well strains at low temperature, in order to get the low temperature-resistant strain with industrial value. [Methods] Mutagenized isolated Q1 by using ultraviolet irradiation and nitrosoguanidine treatment methods, put the strains Q1-4-6 and Q1 which already selected under the 15 °C, 20 °C, 37 °C, compare their growth rate, acid production and the amount of sugar degradation. [Results] Q1 was extracted in homemade yogurt by Maqu pastoralists, the strain was classified into Enterococcus raffinosus according to its morphology, the physiological and biochemical features and 16S rDNA sequence. After several rounds of mutation breeding, select a strain Q1-4-6 that can grow well at low temperatures and genetic traits stable. Compared growth, the amount of acid and sugar degradation between the original strains and mutant strains, we found mutants were better than the original strains. At 37 °C natural conditions, there are rarely differences in growth rate between the original strains and mutants strains, but both of them are a little bit higher than the original strains. The acid amount and growth rate of Q1-4-6 are better than CL04 and CL05 under 15 °C. [Conclusion]?Through complex mutagenesis of UV+NTG, eventually bred a strain Q1-4-6 that growing well at low temperatures with stable genetic traits.
