Light Intensity Regulates LC-PUFA Incorporation into Lipids of Pavlova lutheri and the Final Desaturase and Elongase Activities Involved in Their Biosynthesis

The microalga Pavlova lutheri is a candidate for the production of omega-3 long-chain polyunsaturated fatty acid (LC-PUFA), due to its ability to accumulate both eicosapentaenoic (EPA) and docosahexaenoic acids. Outstanding questions need to be solved to understand the complexity of n-3 LC-PUFA synthesis and partitioning into lipids, especially its metabolic regulation, and which enzymes and/or abiotic factors control their biosynthesis. In this study, the radioactivity of ¹⁴C-labeled arachidonic acid incorporated into the total lipids of P. lutheri grown under different light intensities and its conversion into labeled LC-PUFA were monitored. The results highlighted for the first time the light-dependent incorporation of LC-PUFA into lipids and the light-dependent activity of the final desaturation and elongation steps required to synthesize and accumulate n-3 C20/C22 LC-PUFA. The incorporation of arachidonic acid into lipids under low light and the related Δ17-desaturation activity measured explain the variations in fatty acid profile of P. lutheri, especially the accumulation of n-3 LC-PUFA such as EPA under low light conditions.