糖蜜是白糖炼制过程中的主要副产物，广西是全国耕地白糖的主产区，糖蜜年产量在200万吨以上，当前关于甘蔗糖蜜的资源化利用的研究较为缺乏。L-乳酸广泛应用于食品、医药、纺织、皮革、化妆品及化工领域，具有较高的经济价值。目前，L-乳酸主要由乳酸菌发酵生产或经化学合成获得，但都存在其不可解决的难题。本项目拟通过代谢工程改造酿酒酵母利用甘蔗糖蜜生产L-乳酸进行系统研究，通过表达乳酸脱氢酶编码基因（LDH），在酿酒酵母体内构建一条L-乳酸合成途径。在此基础上，利用基因敲除手段，调控代谢流更多的流向L-乳酸合成途径。通过调控酿酒酵母体内的辅因子NADH/NAD+的比例、筛选适合的L-乳酸转运蛋白等手段，逐步提高L-乳酸的产量。最后，分析并解决甘蔗糖蜜对酿酒酵母代谢生产L-乳酸的限制因素，提高L-乳酸得率。本研究所得的相关成果将丰富酿酒酵母代谢工程改造生产L-乳酸的机制，提高甘蔗糖的附加产值。

Molasses is a main byproduct during sugarcane making process, and more than 200 million tons of molasses each grinding season is produced in Guangxi province, where contributes to the major production of sugar in China. To date, limited research work has been conducted on the resource utilization of molasses. L-lactic acid is widely used in food, medicine, textile, leather, cosmetics and chemical industries, and has a prosperous economic value. To date, L-lactic acid is mainly fermented by lactic acid bacteria or chemical synthesized, however, the two manners all have scabrous problems that restrained efficiency production of this compound. In the present study, we propose to produce L-lactic acid in an engineered Saccharomyces cerevisiae strain which utilize molasses as the main carbon resource. Production of L-lactic acid could be firstly achieved by expression of heterologous gene that encoding lactate dehydrogenase (LDH) in S. cerevisiae. On this basis, genetic manipulations would be conducted to enhance the carbon flux to the biosynthesis of L-lactic acid in S. cerevisiae, such as gene knocking out, regulating NADH/NAD+ ratio and screening of proper transporters which could efficient transport L-lactic acid outside organelle, and so on. Finally, key factors that restrain the fermentation process from molasses would also be analyzed and solved, to increase L-lactic acid production in S. cerevisiae. The results obtained from this study would be helpful to the production of L-lactic acid in S. cerevisiae, and would also be useful to increase the added value of molasses.