Investigation Of Comparative Metabolomics Of Three Microalgae And Improvement Of The Lipid Levels

In order to explore ways of improving lipid productivity of microalgae,metabolomic strategy was employed to systematically study the potential relationshipbetween metabolites and lipid contents in Synechocystis sp. PCC6803, Anabaena sp.PCC7120and Scenedesmus obliquus by gas chromatography-coupled time-of-flightmass spectrometry （GC-TOF-MS） and orthogonal Partial Least Squares （OPLS） model.After potential biomarkers were identified, major parameters including lipid content,lipid productivity and fatty acid composition were studied to explore approaches ofimproving lipid productive of microalgae. Major research results are as follows:A total of74metabolites, including amino acids, organic acids, alcohol amines,lipids and carbohydrates, were identified by GC-TOF-MS in Synechocystis sp.PCC6803, Anabaena sp. PCC7120and S. obliquus. The OPLS-DA model was set up toexplore the relationship between lipid content and intracellular metabolites. The resultsshowed that there was a good correlation between metabolites and lipid contents（R²=0.9916）. Nine metabolites were finally determined as potential biomarkers, whichmight have crucial effects on the lipid content in algae cells. Among them, sucrose,hydroxycitric acid, ethanolamine, glutamic acid, maltotriose and phytol are directlyinvolved in fatty acid metabolism. Further investigation demonstrated that addition ofexogenous ethanolamine （2mM） significantly enhanced the lipid contents in S.obliquus and Chlorella sorokiniana, respectively. Meanwhile, exogenousethanolamine （2mM） significantly increased the contents of fatty acids C16:2andC18:1, while it decreased the content of C18:3.Additionally, the effects of fermentation waste of Saccharomyces cerevisae incombination with ethanolamine on microalgae were studied in this work. These resultsshowed that both biomass and lipid productivity of S. obliquus and C. sorokiniana weresignificantly increased when the fermentation waste after ultrasonic treatment was usedas medium for culturing microalgae. For S. obliquus, its biomass reached to47.54mg·L^-1·d^-1from21.85mg·L^-1·d^-1and lipid productivity increased to7.73mg·L^-1·d^-1from2.35mg·L^-1·d^-1, respectively. For C. sorokiniana, its biomass reached to154.85 mg·L^-1·d^-1from23.75mg·L^-1·d^-1and lipid productivity increased to23.36mg·L^-1·d^-1from2.82mg·L^-1·d^-1, respectively. Based on above results,2mM ethanolamine wasadded into the ultrasonic treated fermentation waste as culture medium at differentculture time. The lipid productivity of S. obliquus reached to14.2mg·L^-1·d^-1from2.57mg·L^-1·d^-1when exogenous ethanolamine was added at0h, while the lipid productivityof C. sorokiniana was increased from2.76mg·L^-1·d^-1to40.9mg·L^-1·d^-1whenethamolamine was added at the early stationary phase.Presently, the relative low lipid productivity of microalgae as feedstock has beenregarded as one of crucial bottlenecks for its industrialization. These findings provideexperimental evidence and new insights into improving lipid productivity ofmicroalgae and treating fermentation waste.