啤酒酵母细胞壁葡聚糖合成代谢与抗自溶性能研究

The autolysis of brewer's yeast during beer brewing siginificantly affects the beer quality and also it affects the usage of yeast. In order to improve the beer quality and reduce the production cost, researches have been focused on the improvement of anti-autolytic capability of brewer's yeast, moreover,understanding the mechanism of brewer's autolysis is the key to the yesat breeding. A lot of researches were focused on the sequential effects caused by yeast autolysis, but not the reason of autolysis. We analyzed the comparative transcriptone of two brewer's yeasts with different anti-autolytic capacity in our early research, and found that in the yeast with better anti-autolytic capacity, the expression levels of cell wall glucan synthesis genes were siginificantly higher than the other yeast. It has been reported that cell wall glucan provide a protection for yeast cells during fermentation, thus, we build the hypothesis that the improved cell wall glucan synthesis is the key to brewer's yeasts' autolysis responses. In order to prove this hypothesis, we plan to knock out and overexpress the genes involved in cell wall glucan biosynthesis pathway so as to reveal the relationship between the cell wall glucan concentration and yeasts' anti-autolytic ability. Moreover, we want to clarify the yeast autolysis response mechanism via anlyzing the promoter sequences and upstream control elements of glucan biosynthesis. This project will explore the autolysis mechanism of brewer's yeast in a new aspect, and provide important theoretical basis for breeding brewer's yeast with better anti-autolytic capability.

在啤酒生产过程中发生的啤酒酵母自溶现象严重影响了成品啤酒的质量和酵母的连续使用代数。为了提高我国啤酒的质量和降低生产成本，抗自溶能力提高的酵母选育和啤酒酵母抗自溶机制成为研究的热点。在以往的研究中，大多数研究都集中在啤酒酵母自溶产物对成品带来的影响，而并没有从源头解决这个问题。我们前期分析抗自溶能力不同的两株啤酒酵母的比较转录组学信息，发现了细胞壁葡聚糖合成代谢在抗自溶能力好的酵母中转录水平显著上调。研究报道细胞壁葡聚糖对酵母细胞有一定的保护作用，所以我们推测葡聚糖合成的加强是啤酒酵母应答自溶压力的一个新机制。为证实这一假设，我们拟通过对葡聚糖合成途径的基因进行敲除和表达，揭示葡聚糖浓度与菌株抗自溶能力的关系；分析细胞壁葡聚糖合成的启动子序列和上游调控元件阐明酵母自溶应答机制。本课题将从新的方面探索啤酒酵母的自溶机制，为指导工业啤酒酵母的抗自溶菌株选育提供重要理论依据。

啤酒酵母是啤酒酿造的灵魂，酵母的质量好坏直接决定了啤酒产品的质量。酵母在低温的啤酒发酵过程中其受到了来自于环境中的各种压力，包括糖、酒精、饥饿等，都会对酵母的细胞结构及其生存能力造成影响，从而影响酵母的发酵能力，导致自溶的发生，最终可能引起啤酒风味的下降以及其抗老化能力的下降。酵母细胞壁葡聚糖在细胞壁合成过程中占有重要的地位，而其中葡聚糖合成酶基因FKS家族基因又起到了非常关键的作用。本研究首先通过对不同抗自溶能力的啤酒酵母进行转录组学以及蛋白组学的研究，分析酵母在自溶过程中各基因的表达水平以及蛋白质表达水平的差异。进一步对FKS家族基因进行调控，发现FKS1和FKS2基因在酵母细胞壁葡聚糖合成过程中起主要作用，而FKS3基因则与前两个基因的作用恰好相反。同时，对三个基因与酵母抗自溶能力进行关联研究发现FKS家族基因通过影响细胞壁的厚度以及影响CWI途径中某些基因的表达从而影响酵母的抗自溶能力。