产低温乳糖酶菌株的筛选、鉴定及酶学性质的研究

Screening,identification of Rahnella sp.R3 producing cold-adapted lactase and its enzymatic properties

从新疆天山冻土中分离获得到一株产低温乳糖酶的耐冷菌。根据形态学方法,生理生化试验、16S rDNA基因序列同源性比对及系统发育树构建对该菌株进行鉴定,结果显示该菌属于拉恩氏菌属(Rahnella sp.),为此命名为Rahnella sp.R3。该菌株最适生长温度和最适产酶温度均为15℃。在最适摇瓶条件下发酵液酶活为5.92 U/mL。该酶为胞内酶,在低温下具有较高活性,最适作用温度为25℃,15℃时的酶活为最高酶活的91%,4℃时的酶活为最高酶活的40%。该酶对热敏感,在65℃保温1 h酶活力完全丧失。粗酶液的最适pH为7.5,在pH 6.5-8.0范围内显示良好的稳定性。一些金属离子对该乳糖酶有一定的抑制作用,其中,Na^+、Ca^(2+)对酶活性影响很小,Cu^(2+)、Al^(3+)、Zn^(2+)对该酶的抑制作用明显。

One cold-adapted lactase producing strain was isolated from Tiansan mount permafrost in the Xinjiang Uygur Autonomous Region. Based on its characteristics of morphology, cultivation, physiology and biochemistry and 16S rDNA sequence alignment, this strain was identified as Rahnella sp. and named Rahnella sp. R3. The optimal growth tempera-ture of the strain and the optimal temperature for producing enzyme were both 15 ℃. Under the optimal fermentation con-ditions, the maximum enzyme activity was 5.92 U/mL. The lactase was intracellular enzyme. Research on its enzymatic properties showed that the lactase was maximally active at 25 ℃ and pH 7.0-8.0. And it had higher enzyme activity at low temperature, 91% at 15 ℃ and 40% at 4 ℃, respectively. The enzyme activity was thermal-sensitive and was unde-tcctable after 1 h incubated at 65 ℃. Some metal ions had inhibiting effects on enzyme activity. Ca^2＋ and Na^＋ slightly re-duced enzyme activity while heavy metal ions, particularly Cu^2＋ , Al^3＋ and Zn^2＋ strongly inhibited enzyme activity.