Dynamic oil body generation in the marine oleaginous diatom Fistulifera solaris in response to nutrient limitation as revealed by morphological and lipidomic analysis

Microalgal lipids are promising useful natural compounds. Microalgae naturally accumulate and store lipids in a subcellular organelle known as an oil body. Understanding the cellular changes occurring during oil body generation is important for unraveling the lipid accumulation mechanisms, variation in lipid homeostasis, and further biotechnological application. A marine oleaginous diatom Fistulifera solaris JPCC DA0580 is a potential candidate for biodiesel and eicosapentaenoic acid (EPA) production. In this study, the lipidomic variations in F. solaris as well as the morphological changes of oil bodies and chloroplasts were monitored following nutrition-depletion. We observed that increases in oil body volume and decreases of chloroplast volume accompanied the increase of neutral storage lipids and the decrease of polar membrane lipids. Changes in chloroplast membrane lipids were coordinated and differed from changes in extraplastidic membrane lipids. The large decrease in polar lipids was concomitant with the significant decrease in newly synthesized EPA-containing chloroplast membrane lipids, although EPA synthesis was not significantly retarded. These findings suggest that F. solaris may selectively shed EPA from chloroplast membrane lipids to generate triacylglycerols (TAGs) after nutrition-depletion. We propose that this remodulation of lipid composition may underlie the observed decrease in chloroplast volume.