Microalga as a sustainable oil crop

Microalgae represent promising sustainable platforms for producing high-value lipid compounds, yet our understanding of how environmental factors regulate carbon partitioning between fatty acid and sterol biosynthesis remains limited. This thesis investigates how nitrogen availability, light intensity, temperature, and salinity affect carbon allocation between fatty acid and sterol across multiple microalgal species, with particular focus on Nannochloropsis oceanica.

Our research revealed distinct strain-specific responses to environmental conditions. Under nitrogen starvation, N. oceanica achieved a maximum triacylglycerol (TAG) content of 37% dry weight (DW) at high biomass-specific photon supply rates (BSPSR), representing a 1.3-fold increase compared to low BSPSR. Temperature shifts enhanced membrane lipid and eicosapentaenoic acid (EPA) synthesis. Additionally, N. oceanica exhibited diurnal cholesterol oscillations, varying 26% between day and night, under salinity stress. High salinity conditions (50 g/L NaCl) increased cholesterol accumulation to 4% DW while simultaneously enhancing TAG synthesis.

The research demonstrates that environmental stresses induce specific carbon partitioning patterns, with nitrogen starvation primarily driving TAG accumulation, salinity stress promoting both sterol and fatty acid synthesis, and temperature shifts influencing membrane lipid composition. These findings advance understanding of microalgal lipid metabolism regulation and provide cultivation strategies for optimizing high-value lipid production in biotechnological applications.