Lipid metabolism in Nannochloropsis gaditana during nitrogen starvation

Abstract

Microalgae are unicellular photosynthetic microorganisms, which can convert light, carbon dioxide and nutrients into multiple products like lipids, proteins and pigments. Even though they are a sustainable source of lipids, higher lipid yields are required to turn the production into an economical feasible process. The microalgae Nannochloropsis gaditana can accumulate large amount of lipids upon nitrogen starvation and it is a natural producer of the omega-3 fatty acid eicosapentaenoic acid (EPA). This thesis focusses on understanding the cellular mechanisms underlying lipid accumulation and developing a process with improved lipid production for Nannochloropsis gaditana. Upon nitrogen starvation Nannochloropsis gaditana can accumulate large amounts of lipids in triacylglycerol (TAG) lipid bodies. EPA can accumulate in both TAG and polar lipid fraction. In this research, we used labelled carbon to measure de novo synthesis and transport of fatty acids during starvation. The expression levels of the genes involved in the pathways were measured for more insight in the active pathways. Furthermore, a strategy to improve lipid accumulation by addition of small amounts of nitrogen to a nitrogen starved culture was tested. Next to that, the amount of light per biomass upon nitrogen starvation was found to be important for TAG accumulation under outdoor light conditions. The research of this thesis was performed within the EU FP7 MIRACLES project under grant agreement No. 613588.