| Schizochytrium sp. is an important oil-producing microorganism, and its single cell oil is rich in Docosahexaenoic acid(DHA). As heterotrophic microorganisms, Schizochytrium sp. can use glycerol and glucose as carbon sources to produce DHA. Fermentation characters are close ly re lated with the environme nt factors. It is meaningful for increasing carbon source utilization to investage the ce lls beha viour under different carbon sources. Phospholipidomics is a powerful tool to study cell responses to the environment. In this study, a liquid chromatography- mass spectrometey(LC-MS) method for analysis of phospholipids in Schizochytrium sp. S31 was established and performed to systematically study the difference of phospholipidomic in Schizochytrium sp. S31 using different carbon sources, which is conducive to the optimization strategies.Firstly, the different effects of glucose and glycerol as carbon source s on the productivity of DHA was elucidated. When the concentration of carbon sources was low, the effects of two carbon sources were similar. When the concentration of carbon source s was high, there were some differences. As soon as the glycerol exhaustion, fermentation time reached 108 h, the highest dry cell weight(62.99 g/L), lipid content(51.03%) and DHA content(50.48%) were obtained. However, the glucose was used up by 96 h and the highest dry cell weight increased to 73.52 g/L and the lipid and DHA contents reached to 45.26% and 40.25% respectively. Glucose promoted rapid growth, and glycerol facilitated the lipid synthesis and DHA accumulation. In addition, lipid accumulation and turnover stages were obtained during the fermentation process, but the phenomenon was clear when using glycerol as carbon source. The shift of NLs to PLs and the increase of PUFA happened in the lipid turnover stage.Secondly, a method for composition analysis of phospholipids by LC-MS was established. Totally 86 kinds of phospholipids were identified in Schizochytrium sp. S31 cells by UPLC-Q-TOF-MS, including 25 species of Phosphatidylcholine(PC), 15 species of Phosphatidylethanolamine(PE), 19 species of Phosphatidylglycerol(PG), 22 species of Phosphatidylinositol(PI), and 5 species of Phosphatidic acid(PA). Then the quantitative analysis of each phospholipid from Schizochytrium sp. S31 was carried out by using UPLC-TQD-MS. The results showed that, PC is the main component(40.8%), followed by PI(27.1%), PA(16.0%), PE(10.4%) and PG(5.7%), but the contents varied because of the different fermentation stages. All phospholipids except PG were found to contain polyunsaturated fatty acids as the predominant fatty acids, such as DHA. While saturated fatty acids, such as C16:0 were predominant in the PG fraction.Finally, the changes of phospholipid contents in Schizochytrium sp. S31 using different carbon sources were measured. When glucose and glycerol were the carbon sources respectively, the variation of 5 kinds of phospholipids in Schizochytrium sp. was as follow: The level of PI and PC increased; The level of PA and PG increased first and then declined; The level of PE is low, its change during the fermentation process was not obvious, showing a decreasing trend generally. Secondly, lipidomics analysis indicated that the two fermentation styles were completely separated; lipid biomarkers contributing most to discriminate the two styles were PG and PI. The level of PI was high when using glucose as carbon source, while the level of PG was high when using glycerol as carbon source. |
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