Study on mutation breeding of Mucor miehei producing milk- clotting enzyme

In order to breed high activity milk- clotting enzyme from strain,Mucor miehei was used as the origin strain and mutagenized by Ultraviolet and Ultraviolet combining lithium chloride.The optimal condition of Ultraviolet was 90 s. After screening repeatedly,a mutant strain UV- 13 was screened. The milk- clotting activity of UV- 13 reached 2448.98 SU / m L and was 42.85% higher than that of the parent strain. The best condition of compound mutation were that the time of Ultraviolet was 90 s,the concentration of lithium chloride was 1.5%.On the basis of multiple mutation,a mutant strain UV- Li Cl- 6 was screened. The milk- clotting activity of UV- Li Cl- 6 reached2703.58 SU / m L and was 57.70% higher than that of the parent strain.Results of the pass- generation test indicated that two strains had good genetic stability.