Isolation And Identification Of A Microbacterium Sp. LW106 Strain Producing Cold-active ?-galactosidase And Its Enzymatic Properties

Objective:Cold-active?-galactosidase,which is suitable for the hydrolysis of lactose in cow milk at low temperature,has a good application prospect in the dairy processing industry.Mining novel cold-active?-galactosidase with high activity at low temperature,which can meet the requirement of low lactose milk production,is still the hotspot of current research.This study is aiming to screen novel strains producing cold-active?-galactosidase from glacier sediments at China No.1 glacier in Tianshan Mountains and elucidate the properties of the cold-active?-galactosidase.Methods:X-gal containing plate method was used for primaary screening,and relative?-galactosidase activity was assayed under low temperature for secondary screening.The target strain was identified by16S rRNA gene sequencing and phylogenetic analysis.The optimum growth and enzyme production condition of the isolate were determined.Enzymatic properties of the?-galactosidase produced by the isolate were also analyzed.Results:1.The strain was identified by studying itscharacteristics of morphology,cultivation,physiology and biochemistry and 16S rDNAsequence alignment.The results showed that the strain belongs to Microbacterium sp.and named Microbacterium LW106.2.The optimal temperature for the growth of LW106 is 20?,the optimal temperature for LW106producing?-galactosidase is 25?.Dissolving starch was the optimal carbon source for LW106 producing?-galactosidase,the optimum medium initial pH was 7.0,and the optimal inoculum size was 3%,liquid volume 30 mL/100 mL.The?-galactosidase production level of up to 2.208�0.043 U/mL was obtained after about 42 h at 25?.3.Preliminary study on its enzymatic properties showed that the optimum pH of?-galactosidase produced by the strain was 6.0,and the optimum reaction temperature was 35?with a relative activity of78%at 4?.The?-galactosidase produced by LW106 showed the best stability at 4?and pH7.0.Metal ion Na+did not inhibit the activity of?-galactosidase produced by LW106,while Ca²⁺activated the?-galactosidase activity up to 139%.The?-galactosidase produced by strain LW106 has good enzymatic properties at low temperature and has research value in the field of low temperature processing of dairy products.