Glycerolipidomics Of Two Marine Microalgal Species

Microalgae are the promising resource for biodiesel feedstocks because of its capacity for triacylglycerol(TAG)accumulation.Polar glycerolipids have big contribution for TAG accumulation by providing acyl group or diacylglycerol(DAG).In-depth understanding of polar glycerolipids metabolic pathway and the relation with TAG accumulation is the prerequisite to enhance its TAG production.Microalgal glycerolipid metabolism has been explored by lipidomics as the indispensable tool.On the one hand,Glycerolipid metabolic pathways could be discovered or constructed from the role of chemical biology through the identification of lipid metabolic intermediate.On the other hand,the metabolic characteristics of glycerolipid response to environmental variation could be obtained through the quantification of lipid metabolic intermediates.In this dissertation,the analytical platform of microalgal glycerolipidomics was developed.And based on glycerolipidomic the glycerolipids variation in reponse to nitrogen and phosphorus deprivation have been studied.Then the metabolic pathways have been proposed.The contributions of polar glycerolipid for TAG accumution were explored in two marine microalgae Nannochloropsis oceanica and Isochrysis zhangjiangensis.1.The detection platform of microalgal glycerolipidomics was developed.It consists of the identification of glycerolipid classes and species baesd on the precursor and neutral loss scan modes of HILIC/Q-trap and the analysis of acyl structure of species based on rapid MSn scan of C8/Orbitrap.Two marine microalgae glycerolipid databases were developed including 228 species covering 9 classes in N.oceanica and 175 species covering 10 classes in I.zhangjiangensis.The glycerolipid database of I.zhangjiangesis the first time to be studied systematically,and for the glycerolipid database of N.oceanica there are 172 new molecule species than literature.2.Based on glycerolipid molecule species profiling and variations under nitrogen deprivation it has been explored for the polar glycerolipid metabolic pathways and the function in TAG accumulation in N.oceanica.Results showed that phosphatidylcholine(PC)served as the carrier of C18 fatty acids(C18 FA)desaturation whereas phosphatidylethanolamine(PE)and diacylglyceroltrimethyhomoserine(DGTS)served as the carrier of eicosapentaenoic acid(EPA)biosynthesis and provide EPA to synthesis of EPA-containing monogalactosyldiacylglycerol(MGDG).And after nitrogen deprivation,PC was the major contributor to turn over acyl 16:0 and 18:1 for TAG accumulation in N.oceanica.3.It was the first time to disclose the metabolic mechanism of polar glycerolipid remodeling on phosphate starvation and recovery in N.oceanica based on glycerolipidomic.This process demonstrated new glycerolipid metabolic characteristics under phosphorus stress which was different from those under the nitrogen stress.Results showed that under phosphate deprivation,DGTS served as the central intermediate in glycerolipid remodeling via acting as carrier of C18 FA desaturation by replacement of PC,maintaining the biosynthesis of EPA and providing the EPA for the chloroplast glycolipid.And in the process of resupplying phosphate,PC was increased by hydrolyzed TAG as the acyls donor for PC biosynthesis via DAG.4.In I.zhangjiangensis MGDG served as the main carrier of C18 FA desaturation.Betaine lipids DGTS and diacylglyceryl carboxyhydroxymethylchiline(DGCC)served as the acyl donor involved in the metabolism of acyl transfer.And after nitrogen deprivation,MGDG was the donor to turn over acyl 16:0 and 18:1 for TAG accumulation.TAG de novo biosynthesis pathway has been identified as the critical pathway for high level microalgal TAG accumulaton,by comparing the difference of the source of acyl group in TAG biosynthesis between I.zhangjiangensis and N.oceanica.This point will be one of the most essential factors that should be considered to guide the screening of oleaginous photosynthetic microalgae.In this dissertation,the glycerolipid metabolic pathway and the response to nitrogen and phosphorus deprivation were explored in N.oceanica and I.zhangjiangensis.Results enriched the knowledge of microalgae lipid metabolism and revealed the diversity of the lipid functions and metabolism in microalgae.It provides the basis for strengthening microalgae TAG accumulation based on genetic reconstruction.Meanwhile the metabolic pathway constructed by lipidomics,provides the possibility to discover new enzymes from chemical biology.