发酵乳生产过程中乳酸菌代谢多样性的研究

Fermented dairy products are main products that lead the future development of China's dairy industry. Their quality depends largely on the lactic acid bacteria (LAB) fermentation agent. Based on Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus strains isolated from the traditional fermented dairy products that have been preserved at the Lactic Acid Bacteria Collection Center at Inner Mongolia Agricultural University, PacBio SMRT sequencing technique was used to complete the genome maps and comparative genomics analysis of different strains. On the basis of this, the transcriptome and proteomics methods were used to analyze the metabolic diversity of the strains in the production of fermented dairy products. For the key genes, digital PCR was used to validate its biological function in order to reveal the mechanism of gene expression regulation between different strains. The implementation and further completion of this project will lay a solid theoretical foundation for the utilization of LAB resources and the development of fermentation agent.

发酵乳制品是引领我国乳品工业未来发展的主导产品，其质量优劣在很大程度上取决于乳酸菌发酵剂。本课题依托内蒙古农业大学乳酸菌菌种资源库（LABCC），以分离自传统乳制品的Streptococcus thermophilus和Lactobacillus delbrueckii subsp. bulgaricus菌株为研究对象，采用PacBio SMRT测序技术完成不同菌株基因组精细图谱的绘制及比较基因组学分析。在此基础上，联合转录组学和蛋白质组学方法对菌株在发酵乳制品生产过程中的代谢多样性进行全方位分析。针对部分关键基因，进一步使用数字PCR技术对其生物学功能进行验证，以期揭示种内不同菌株间代谢特性差异发生的基因表达调控机制。该项目的实施和完成，可为乳酸菌发酵剂的研究开发及利用奠定坚实的理论基础。

作为基础发酵剂，Streptococcus thermophilus和Lactobacillus delbrueckii subsp. bulgaricus被广泛应用于各类发酵乳制品的加工生产。目前针对它们的研究大多集中于发酵乳生产过程中的功效与作用，而对于其发酵代谢特性的调控机理尚不清楚。本研究以分离自传统乳制品的Streptococcus thermophilus和Lactobacillus delbrueckii subsp. bulgaricus菌株为研究对象，采用多组学方法对菌株在发酵乳生产过程中的代谢多样性进行全方位分析。研究结果显示，Streptococcus thermophilus基因组大小平均为1.89Mb，GC含量平均为39.00%，编码区数量平均为2075；Lactobacillus delbrueckii subsp. bulgaricus基因组大小平均为1.84Mb，GC含量平均为49.77%，编码区数量平均为1813。Streptococcus thermophilus和Lactobacillus delbrueckii subsp. bulgaricus含有不同的蛋白水解系统。两个菌种含有不同种类的肽转运系统和内肽酶，且与Streptococcus thermophilus相比，Lactobacillus delbrueckii subsp. bulgaricus含有更丰富的细胞壁蛋白酶。在发酵乳生产过程中，Streptococcus thermophilus和Lactobacillus delbrueckii subsp. bulgaricus通过调控碳水化合物代谢、氨基酸代谢、氨基酸转运及代谢以及核苷酸代谢相关基因、蛋白或者代谢产物提高其生长和生存效率，同时赋予发酵乳优良的风味、丰富的营养价值。在牛乳、褐色牛乳及乳清的发酵过程中，Streptococcus thermophilus和Lactobacillus delbrueckii subsp. bulgaricus均体现出良好的代谢特性。上述研究结果，一方面可为更好的开发利用Streptococcus thermophilus和Lactobacillus delbrueckii subsp. bulgaricus奠定理论基础，另一方面也可为优化发酵乳生产工艺提供重要的理论依据。