PREFERENTIAL SYNTHESIS OF VERY LONG CHAIN POLYUNSATURATED FATTY ACIDS IN EUTREPTIELLA SP. (EUGELNOZOA) REVEALED BY CHROMATOGRAPHIC AND TRANSCRIPTOMIC ANALYSES

Algal lipids are a fundamental energy source in the ecosystem and material for biofuel production, but their production and regulation remains unexplored in many species including the common coastal phytoplankton Eutreptiella spp. Using gas chromatography-tandem mass spectrometry (GC/MS/MS), we discovered 24 types of fatty acids (FAs) in Eutreptiella sp. with unsaturated C24 FAs and a relatively high proportion of long chain unsaturated FAs. The abundances of C16, C18 and saturated FAs decreased when phosphate in the culture medium was depleted. Among the 24 FAs, docosahexaenoic acid (22:6) and eicosapentaenoic acid (20:5) were the most abundant, suggesting that Eutreptiella sp. preferentially invests in the synthesis of very long chain polyunsaturated fatty acids (VLCPFA), making this alga nutritionally valuable to grazers. Further transcriptomic analysis revealed that Eutreptiella sp. likely synthesizes VLCPFA via Δ8 pathway and uses type I and II fatty acid synthases. Using RT-qPCR, we found that some of the lipid production genes, such as β-ketoacyl-ACP reductase, fatty acid desaturase, acetyl-CoA carboxylase, acyl carrier protein, ∆8 desaturase, and Acyl-ACP thioesterase, were more actively expressed during light period. In addition, were more highly expressed in the high lipid-producing light period, suggesting a linkage between photosynthesis and lipid production.