Isolating,identification and mutation of a high protease producing strain in Douchi

Objective:To improve the ability of protease producing,a high-yielding strain of protease from fermented Douchi was isolated,and the enzyme activity of this strain after ultraviolet mutagenesis was identified.Methods:Firstly,the protease producing strains were isolated from Douchi by casein plate method.By comparing the enzyme activity of proteases after fermentation,the strains which can produce most proteinase were selected.And then identified the strain breed,studied the enzymology and did mutagenize in order to elevate their ability about producing proteinase.Finally a high protease producing strain was obtained in Douchi.Results:According to the results of microscope testing and physiological and biochemical characteristics,the strain B isolated from Douchi belongs to the bacillus licheniformis,the activity of enzyme reached 2360.80U/mL.The best mutagenesis time of this strain was 120s,colonies mortality rate was 66.68%,the high protease producing strain was B-14,the activity of enzyme reached 2922.90U/mL which was 23.81% higher than the initial strain and showed fine stability.Conclusion B-14 high protease producing strain was obtained after selection and mutagenized by UV.