益生菌是一类摄入一定数量后对宿主有益的活性微生物的总称。乳酸菌在内的非人源益生菌发挥益生作用的前提，是其必须能黏附于宿主细胞表面，并定殖于人体肠道。近年来研究表明乳酸菌表面分泌的一些胞外大分子物质，如胞外多糖（EPS）参与了相关的锚定、黏附过程，但对其构效关系和内在作用机制了解甚微。在前期研究中，本课题组从新疆传统药食兼用型赛里木酸奶中分离到一株高产胞外多糖（EPS）的瑞士乳杆菌MB2-1，该菌株具有很强的肠道黏附活性。本课题拟建立基于生物信息学和分子生物学的瑞士乳杆菌MB2-1 EPS缺失突变株选择性定向构造方法，构建不同类型EPS缺失突变株；明确不同类型和种类EPS在应对消化道压力及在肠道黏附、菌群和免疫调节中所起的作用；定性、定位、定量揭示EPS结构与瑞士乳杆菌MB2-1肠道锚定、黏附、定殖及活性间的关系，并阐明其作用机制；为非人源益生菌功能性乳制品的开发提供坚实的理论和应用基础。

Probiotics are defined as “live microorganisms which when administered in adequate amounts confer a health benefit on the host”. Non-humanized probiotics, including lactic acid bacteria, play a prebiotic effects role as a prerequisite that they must adhere to the host surface and colonize the human intestine. Recent studies showed that some extracellular macromolecules secreted on the surface of lactic acid bacteria, such as exopolysaccharides (EPS), are involved in the related anchoring and adhesion processes. However, very few studied have investigated the structure-activity relationship and intrinsic mechanism of adhesion effect. In our previous studies, Lactobacillus helveticus MB2-1, a strain isolated from traditional Sayram yogurt from Xinjiang province showed a high yield of exopolysaccharides (EPS), which has a strong intestinal adhesion activity. This project intends to establish a method for selective oriented structure of EPS based on bioinformatics and molecular biology, to construct different types of EPS deletion mutants. In addition, the different kinds and types of EPSs in response to gastrointestinal pressure, intestinal adhesion, microflora and immune regulation will be determined. Furthermore, the relationship between the structure of EPS and the intestinal anchoring, adhesion, colonization and biologic activity of L. helveticus MB2-1 will be revealed in qualitative, positioning and quantitative manners. Its mechanism of action will also be clarified. This project is considered to provide solid theoretical and practical basis for development of non-humanized probiotics' functional dairy products .