作为美国FDA认可并推荐的食品营养组分，天然虾青素(可食用红色素)存在于三文鱼等多种食品中。虾青素的超级抗氧化性赋予其多种有益于人体健康的功能，但其发酵生产技术仍不成熟，导致虾青素价格昂贵，市场缺口巨大。相比虾青素生产应用较多的雨生红球藻，食用小球藻Chlorella zofingiensis能利用有机碳源高密度异养发酵积累虾青素，而且不需要光，具有规模化发酵生产虾青素的巨大潜力，但目前其虾青素的含量仍有待提高。本研究拟利用酶的定向进化分析虾青素合成的关键酶β-胡萝卜素酮化酶（BKT）和羟化酶（CHY）结构和氨基酸组成与酶活力的关系。在此基础上利用定点突变创建功能增强的BKT和CHY基因并建立具高效积累虾青素的小球藻突变株，同时结合发酵工程技术引导小球藻细胞内碳代谢流向虾青素合成，阐明发酵过程中小球藻合成积累虾青素的调控机制，为利用小球藻发酵技术工业化生产天然虾青素打下坚实的理论基础。

Approved and recommended as a nutraceutical by the United States Food and Drug Administration, astaxanthin, an edible red pigment, is found in a variety of foods like salmon. Astaxanthin has been demonstrated to possess extremely strong antioxidant activity and be beneficial to human nutrition and health. The global market of astaxanthin has grown very fast recently. Nevertheless, due to the high production cost, astaxanthin is still very expensive. At present, Haematococcus pluvialis is used for commercial production of astaxanthin. Although Chlorella zofingiensis has relatively low cellular astaxanthin content compared to H. pluvialis, it can grow heterotrophically in the dark using high-cell density fermentation technology on a large scale. Therefore, growing C. zofingiensis for the production of astaxanthin possesses tremendous potential. The present project aims to study the relationship between the enzymatic activities and amino acids compositions of the two key enzymes, β-carotene ketolase (BKT) and β-carotene hydroxylase (CHY), which are involved in astaxanthin biosynthesis in C. zofingiesis. Coupled with the structure-function relationship analysis and site-directed mutagenesis, the functional-enhanced BKT and CHY genes will be created and introduced into the algal genome for enhanced production of astaxanthin in the organism. Furthermore, we will use metabolic engineering and fermentation technology to direct cell carbon sources towards astaxanthin biosynthesis so as to greatly enhance the production of astaxanthin in C. zofingiensis. The present study will lay a solid foundation for employing C. zofingiensis as cell factories for commercial production of high-value natural astaxanthin by fermentation technology.