【作者】 郑华军；

【导师】 赵国屏；

【作者基本信息】 复旦大学 ， 微生物学， 2010， 博士

【摘要】 保加利亚乳酸杆菌是用于奶酪和酸奶生产的重要乳酸细菌,但除两个模式菌株外,还没有报道工业菌株完成测序。本文论述了乳品工业生产用菌株—保加利亚乳酸杆菌2038株的全基因组测序。基因组序列分析显示了保加利亚乳酸杆菌适合工业应用的一些生理特征以及对牛奶环境的适应性进化,如丰富的蛋白水解系统、高效利用乳糖产生乳酸、产生极低的风味物质、耐酸而不耐氧、与嗜热链球菌共同生长具有相互促进生长作用以及退化的氨基酸合成能力等。同时与模式菌株进行的比较基因组学分析,发现了保加利亚乳酸杆菌2038株所特有的294个基因,通过功能分析发现这些特异基因在生理功能上赋予了2038株独特的适用于酸奶生产的优点,如合成赖氨酸、产独特的胞外多糖、应急性产生甲酸、把天冬氨酸转化为丙酮酸、特异的限制修饰系统、更强大的错配修复系统以及更强的蛋白分解能力等。通过基因进化和系统发育关系分析,发现保加利亚乳酸杆菌2038株在进化关系上比两株模式菌株更接近它们的共同祖先。人工选择带来的负选择压力和自身的错配修复系统,可能阻止了2038株基因组的退化,从而确保其自身的优良性状不发生变异,保持适于酸奶生产。更多还原

【Abstract】 Lactobacillus delbrueckii subsp. bulgaricus is an important species of Lactic Acid Bacteria (LAB) used for cheese and yogurt fermentation. There was no genomic sequence for any industrial strains of Lb. bulgaricus available besides that of two academic strains. The genome of Lb. bulgaricus 2038 that has been employed for manufacturing yogurt since 1989 by Meiji Dairies Corporation, was completely sequenced and annotated.Lb. bulgaricus 2038 displays properties common for Lb. bulgaricus strains but favorable or essential for industrial applications, including abundant proteolytic system, high efficient lactate production, low flavor compounds production, acid stress tolerance, protocooperation with Streptococcus thermophilus, and degenerated amino acid biosynthetic capacity. Comparative genomic analysis against the two academic strains also identified 294 genes as Lb. bulgaricus 2038 specific, endowing this strain with specific features for yogurt production, such as extra-capabilities in lysine biosynthesis, EPS production, salvage formate production, aspartate-related intermediate metabolism, two complete typeⅡRM systems and more power proteolytic capacity over the academic strains.Analysis of gene evolution as well as phylogenetic analysis illustrated that gene loss was a common phenomenon in evolution of Lb. bulgaricus strains. Genetically, Lb. bulgaricus 2038 seems closer to the common ancestor than the other two academic strains. A strict maintenance process of Lb. bulgaricus 2038 for industrial purposes apparently slowed down the genome decay and sustained a gene network that ensures the optimal suitability for industrial production of yogurt.更多还原