基于稳定同位素标记脂质组学的磷限制下微拟球藻甘油酯代谢重组机制研究

Microalgae utilize the glycerolipid remodeling mechanism of non-phosphorus lipid replacing phospholipid against phosphorus (P) depletion in aquatic ecosystems; this mechanism is of great significance in understanding the ecological imbalance caused by P limitation. Previous studies have indicated that P limitation induced the glycerolipid remodel occurring in Nannochloropsis oceanica and betaine lipid replacing the phospholipid and playing as the central hub of glycerolipid metabolism. Due to the complexity of glycerolipid metabolism, two crucial aspects of the glycerolipid remodelling mechanism remain unresolved: (1) the acyl transfer pathway of glycerolipids in the remodeling process, (2) the metabolic role of DGTS after replacing PC. Here, the high resolution lipidomics of the polar glycerolipid as the break through point, the dynamic process of the acyl synthesis, transformation and remodeling under P limitation is first explored by using 13C isotope labeling. Based on the UPLC-MS quantitative analysis, developed the evolution model of glycerol lipid remodeling under P limitation, and combining the distribution information of lipid subcell and the transcriptional information of related genes, to discover the process of betaine lipids gradually replacing phospholipids under P limitation. Finally, combining with the dynamic change of unsaturated fatty acids in the glycerolipid remodeling process, the mechanism of the recombinant metabolism of glycerolipid under the restriction of P and the metabolic function of betaine lipid in this process were revealed. The results of this project will enhance our understanding of lipid metabolism in microalgae and the relationship of between the composition of oceanic compounds and the nutrient environment. Thus, our study will provide new bioinformation on marine ecosystems and contribute to the development new technologies for regulating microalgae cultivation.

微藻以磷脂为磷源、以非磷脂质取代磷脂应对环境磷限制，深入研究这一过程在认识磷限制引发的水生生态失衡方面具有重要的意义。前期研究发现，磷限制诱导微拟球藻发生甘油酯重组代谢，甜菜碱脂取代磷脂成为主要极性甘油脂。由于脂代谢的复杂性，对于重组过程缺乏认识，尤其对甜菜碱脂在上述重组过程中的作用是一个未解之谜。本项目以甜菜碱脂、磷脂和糖脂在磷胁迫条件下高分辨脂质组学研究为突破口，首次通过13C同位素标记探索磷限制下微藻甘油酯的合成、转化及重组的动态过程；以液质定量为基础，建立甘油酯磷限制演化模型，并结合脂质亚细胞分布信息和相关基因转录信息，确定甜菜碱脂在磷限制下对磷脂逐步取代的过程；最终结合特定不饱和脂肪酸在脂质分布信息的动态变化规律，揭示磷限制下甘油酯重组代谢的机制及甜菜碱脂在这一过程中的代谢功能，拓展对微藻甘油酯代谢与水生营养环境间关系的认识，为水生生态环境研究和微藻油脂调控积累提供理论基础。

为深入了解磷元素限制下微藻细胞内的脂质代谢重组机制，本项目建立了细胞内多聚磷检测方法及基于13C同位素标记的脂质组学方法。通过建立的分析平台对磷限制过程甘油酯代谢进行分析。结果显示多聚磷的存在对细胞应对磷的限制具有重要影响。在磷限制后48h内， 细胞仍可以大量合成PC作为极性脂代谢中心枢纽，减缓磷限制的影响。DGTS含量的增加，并且其酰基的主要来源为新合成。说明PC与DGTS之间并给直接转换，或者转换率非常低。DGTS在磷限制后会替代磷脂的部分功能，满足细胞对极性脂的需要。此外我们通过寻找外源方式，研究了同时改善限制下同时增加微藻生物量和高值产品的方法。外源褪黑素通过延缓氮胁迫引起的氧化损伤，光合色素损失，激活抗氧化酶，降低脂质过氧化等方式提高氮胁迫下的生物量及脂质含量。利用碳纳米材料光谱转换性能改善光限制下微藻固碳。微藻叶绿素能有效地吸收和利用了紫外线，使其光合活性、生物量和蛋白质产量显著提高。