乳制品是优质营养物质，乳糖酶是乳制品消化吸收的关键功能酶。乳糖酶缺乏症（LD）在我国公民中极为普遍，致使这些人不能很好吸收牛奶里的营养物质。现行的体外发酵、补食乳糖酶等措施仅能改善乳糖不耐症，在此我们提出一种全新的治疗LD策略，即利用工程技术在益生菌乳酸乳球菌表面展示乳糖酶，通过此全细胞催化剂在体内、外水解乳糖，解决LD。项目拟选择分子量适中、单亚基即有酶活性的嗜酸乳杆菌β-半乳糖苷酶为靶标，在其N端设计有乳酸乳球菌的启动子、分泌信号肽及肽聚糖锚定基序，整合入乳酸乳球菌基因组，使用食品级的乳链菌肽抗性基因作为筛选标记，使融合蛋白在乳酸菌中高效表达并实现分泌，通过锚定基序与肽聚糖的聚糖骨架非共价结合而展示在细菌表面，使细菌成为一个"大号乳糖酶"；进一步对其生长、展示条件进行测定、优化，并测定重组菌作为全细胞催化剂的酶学性质；再利用小鼠进行初步的安全性评价，为乳糖酶工程菌的应用提供实验依据。

Dairy products are important dietary sources of nutrients, such as protein, calcium and vitamins. These foodstuffs also contain lactose, the carbohydrate of dairy, which is not absorbed in its intact form, its hydrolysis into glucose and galactose by way of the action of the lactase (β-galactosidase) being necessary. The level of lactase activity is elevated until the weaning stage and declines with advancing age, a phenomenon called lactase deficiency (LD). LD can produce lactose malabsorption and intolerance, which is characterized by symptoms such as diarrhea, abdominal distension, flatulence, cramps, and abdominal pain after the intake of dairy products. Therefore, LD can induce the malabsorption of dairy nutrients. LD is very popular in the world, especially in our country. There are several ways have been found to manage LD. In this work, we present a new method to solve LD: display lactase on the cell-surface of Lactococcus lactis (L. lactis), which can hydrolyze lactose in vivo and in vitro. β-galactosidase of Lactobacillus acidophilus is monomeric enzyme with moderate molecular mass (76.6 kDa). The N-terminal of the enzyme will be fused with promoter, secretion signal and anchoring motifs, which construction a cell-surface display system. By using the system, the expressed fusion protein will be secreted out of L. lactis cell, and will be binded on the peptidoglycan of L. lactis by non-covalent interaction. Then the cell-surface display system fused with nsr gene (nisin-resistance gene, food grade selective marker) will be integrated in genome DNA of L. lactis. After that, the growth and display conditions of the engineered L. lactis will be optimized, and the enzyme characterization of the engineered L. lactis as whole cell biocatalyst and its preliminary safty will be study also.