一株产凝乳酶解淀粉芽孢杆菌的筛选、鉴定及酶学性质

采用酪蛋白培养基,从甘南牦牛放牧区分离筛选产凝乳酶细菌。通过形态学、生理生化特征和16SrDNA序列同源分析对菌株进行鉴定,并对该菌株所产凝乳酶的特性进行了研究。从牧区采集的56个样品中共筛选得到6株产凝乳酶细菌,复筛得到一株凝乳活力高、蛋白水解力低的菌株GN4.1,经鉴定为解淀粉芽孢杆菌(Bacillus amyloliquefaciens),在麸皮培养基中发酵48h,凝乳活力可达1011.56SU/mL,蛋白水解力为14.61U/mL。凝乳酶的最适作用温度为60℃,65℃加热10min后凝乳活力丧失;最适作用pH为5.5,在pH3.5～8.5内稳定性较好。预期该菌株所产凝乳酶有用于乳品加工业的潜力。

Study on isolation,identification of Bacillus amyloliquefaciens producing chymosin and enzyme properties

The casein culture medium was used to isolate milk-clotting enzyme producing bacteria from soil of yak grazing district in Gannan County.Strain identification was carried out based on the morphology,physiology,biochemical test and 16S rDNA sequences analysis,and the property of the milk-clotting enzyme produced by the strain was studied.Six bacteria producing milk-clotting enzyme were screened out.Furthermore,one bacterium GN4.1 had the highest milk-clotting enzyme activity and the lowest protein hydrolyzed enzyme activity,identified as Bacillus amyloliquefaciens.The milk-clotting enzyme activity and the protein hydrolyzed enzyme activity of GN 4.1 was 1011.56SU/mL and 14.61U/mL after fermentation for 48h,respectively.The optimal reaction condition for milk-clotting enzyme was at 60℃,pH5.5.The activity was stable at pH ranging from 3.5 to 8.5 but totally lost after heating at 65℃ for 10min.The milk-clotting enzyme produced by strain GN 4.1 might have the potential applicatin in dairy industry.