Microalgae as a sustainable oil crop

Microalgae offer a sustainable alternative to traditional oils and sterols, and Nannochloropsis is particularly promising due to its high triacylglycerol (TAG), eicosapentaenoic acid (EPA), and cholesterol content. This thesis describes research on how environmental conditions regulate sterol and fatty acid metabolism in Nannochloropsis oceanica. The metabolic responses to nitrogen starvation combined with different biomass-specific photon supply rates, cold shock and salinity stress were studied by comparative strain screening, followed by experiments in a controlled photobioreactor.
The findings reveal that carbon allocation is environmentally regulated rather than direct competition between lipid pathways. Nitrogen starvation and high light stimulated TAG accumulation, while cold stress enhanced membrane lipids and cholesterol, and salinity stress enhanced both TAGs and cholesterol. Additionally, sterol and fatty acid biosynthesis showed circadian patterns, enabling optimization through strategically timed harvesting. 
Overall, the results described in this thesis advance understanding of lipid regulation and provide practical cultivation strategies for developing Nannochloropsis as a sustainable platform for the production of sterols and fatty acids for different biotechnological applications.