Abstract
The marine oleaginous diatom Fistulifera solaris JPCC DA0580 is a candidate for biodiesel production because of its high lipid productivity. However, the substantial eicosapentaenoic acid (EPA) content in this strain would affect the biodiesel quality. On the other hand, EPA is also known as the essential health supplement for humans. EPAs are mainly incorporated into glycerolipids in the microalgal cell instead of the presence as free fatty acids. Therefore, the understanding of the EPA biosynthesis including the incorporation of the EPA into glycerolipids especially triacylglycerol (TAG) is fundamental for regulating EPA content for different purposes. In this study, in order to identify the biosynthesis pathway for the EPA-containing TAG species, a lipidomic characterization of the EPA-enriched polar lipids was performed by using direct infusion electrospray ionization (ESI)-Q-TRAP-MS and MS/MS analyses. The determination of the fatty acid positional distribution showed that the sn-2 position of all the chloroplast lipids and part of phosphatidylcholine (PC) species was occupied by C16 fatty acids. This result suggested the critical role of the chloroplast on the lipid synthesis in F. solaris. Furthermore, the exclusive presence of C18 fatty acids in PC highly indicated the biosynthesis of EPA on PC. Finally, the PC-based acyl-editing and head group exchange processes were proposed to be essential for the incorporation of EPA into TAG and chloroplast lipids.
Highlights
Over the past several decades, biofuel production has attracted much interest due to the approaching exhaustion of fossil fuels and their negative impacts on climate
In order to examine how eicosapentaenoic acid (EPA) is synthesized and incorporated into TAGs in F. solaris, the polar lipid profile including the information of fatty acid composition and positional distribution was elucidated by direct infusion electrospray ionization (ESI)-Q-TRAP-MS/MS, through which the intact molecular structures of lipids can be determined
These results suggest that diatoms may share the EPA synthesis mechanism in which PCs play a central role, we have previously demonstrated that the EPA synthesis pathway in
Summary
Over the past several decades, biofuel production has attracted much interest due to the approaching exhaustion of fossil fuels and their negative impacts on climate. Some microalgal strains, which were determined to produce high content of EPA and DHA [13], are the potential alternative source of ω3-LCPUFAs. The understanding of the biosynthesis pathway for ω3-LCPUFA and the assembly of ω3-LCPUFA into lipids is the essential task to control ω3-LCPUFA content in microalgae by means of metabolic engineering. A pennate diatom, Phaeodactylum tricornutum has been used as one of the model organisms for studies in ω3-LCPUFA synthesis [14,15] due to its high content of EPA [16], available genome information [17] and easy transformation [18,19]. The distribution of EPA and its precursor fatty acids in polar lipids was analyzed with direct infusion electrospray ionization (ESI)-Q-TRAP-MS/MS in order to deeply understand the polyunsatulated lipid synthesis in F. solaris.
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