基于三代测序技术研究嗜热链球菌胞外多糖的生物合成机制

乳酸菌胞外多糖具有增加发酵乳粘度，防止乳清析出，增强凝乳强度等特性，是目前食品科学领域的研究热点之一。随着高通量测序技术的快速发展，更多乳酸菌胞外多糖基因簇被发现和研究，但对菌株与胞外多糖生产相关的整体代谢机制缺乏足够的认识。本项目以产胞外多糖的嗜热链球菌为研究对象，采用三代测序技术并结合生物信息学分析方法，从基因组水平对产胞外多糖的嗜热链球菌进行全面系统的调查研究，构建产胞外多糖嗜热链球菌的基因组尺度代谢网络，分析不同菌株在序列、结构、遗传修饰及转录水平上的差异，预测能影响胞外多糖表型特征的关键靶基因。在此基础上，利用已建立的Cre-LoxP系统构建EPS突变株，分析上述靶基因的缺失对胞外多糖表型特征的影响，阐明嗜热链球菌胞外多糖表型差异产生的分子机制，为嗜热链球菌及其生产的胞外多糖的研究和开发工作提供科学依据和理论指导。

The exopolysaccharides (EPSs) of lactic acid bacteria can increase the viscosity of acidified milk, prevent the precipitation of whey, and enhance curd strength; thus, they are a focus of research in food science. The development of high-throughput sequencing has facilitated the discovery and investigation of the EPS-encoding gene clusters of lactic acid bacteria, but our understanding of EPS biosynthesis is incomplete. Using a third-generation sequencing technique and bioinformatics analysis, we uncovered the genome-scale metabolic network of Streptococcus thermophilus, which produces EPSs, and analyzed differences in sequence, structure, genetic modification, and transcriptional level among strains to identify genes that influence the EPS composition. Additionally, we used the Cre-LoxP system to knock out the identified genes to construct EPS mutant strains, and analyzed the effect on EPS composition. Our findings will facilitate further research on the EPSs of S. thermophilus.