Cloning, Expressing And Characteristics Study Of β-D-galactosidases From Athrobacter Sp.

The study of the Psychrophiles was interesting because of their survival at the low temperature.To adapt such cold environment,cold active enzymes were produced. Among these,β-D-galactosidase had good prospect for commercial use.According to the investigation,about one tenth people in the world had the trouble in the metabolism of lactose that was called lactose intolerant.When these people drunk the milk,lactose would cause their unhealthy,such as diarrhea,vomiting.So we mainly addedβ-D-galactosidase directly in the process of milk.Cold activeβ-D-galactosidases had merits that they did not change the milk's flavor during the treatment of lactose.We had screened one strain producingβ-D-galactosidases which was named On14,and detected whether it produced cold activeβ-D-galactosidases.The result indicated that there are two types ofβ-galactosidases in the On14 namedβ-GalⅠ(3090bp),β-GalⅡ(2052bp).Sequences alignment showed thatβ-GalⅠandβ-GalⅡbelonged to glycosyl hydrolysis family2 and lacG respectively.The detection of the enzyme activity indicated thatβ-GalⅠwas cold activeβ-D-galactosidase,in contrast.β-GalⅡwas mesophilic.Their optimum temperature was 5℃and 37℃respectively. Because of cold activeβ-GalⅠ,we expressed and purified it.The purifiedβ-GalⅠwas added to the milk and detect the efficiency of hydrolyzing lactose by HPLC.Results suggested it hydrolyzed lactose well in the milk and had potential for commercial use.As the intracellularβ-D-galactosidases,it could suggest that the couple of isozymes played different roles in the carbon metabolism in the ON14.RT-PCR results suggested as the lactose was sole carbon resource;differentβ-D-galactosidases would express highly to hydrolyze lactose,due to the different temperature inducing.In the Arthrobacter sp,it was first report that different temperature induced different types ofβ-galactosidases expression.