Modulation of lipid metabolism in Nannochloropsis spp.: understanding metabolic pathways towards the production of oils

Anthropogenic greenhouse gas emissions drive climate change, with agriculture contributing nearly to one-third of global emissions. Significant impacts arise from land use changes like deforestation for livestock and crops, leading to CO2 release, soil degradation and ecosystems loss. Fertilizer and water overuse exacerbate environmental issues. The growth of the global population (projected to exceed 9.5 billion by 2050) will demand increased food production, particularly in oil crops, which occupy 20% of cultivated areas and contribute to land use challenges, especially with palm oil. Microalgae, such as Nannochloropsis spp., offer a sustainable alternative for lipid production. Known for high photosynthetic rates and valuable biomass, these organisms can grow on non-arable land, using seawater and waste CO2. Nannochloropsis spp. is notable for accumulating lipids and eicosapentaenoic acid (EPA). In the last decades, genetic engineering has been focusing on enhancing lipid yield and understanding fatty acid biosynthesis. This thesis explores genetic modifications in Nannochloropsis spp. to optimize lipid production. In Chapter 2, a N. gaditana strain with a knockout for plastid desaturase SAD showed a decrease in palmitoleic acid and increased unsaturated fatty acids content, a fatty acid profile more similar to that of palm oil. Chapter 3 examines overexpression of β-ketoacyl-ACP-synthase (KAS), revealing changes in fatty acid profiles without compromising growth or lipid yield yet affecting photosynthesis under nitrogen limitation. Chapter 4 investigates the role of a unique Apicomplexa-like TPT transporter in carbon flux regulation, finding that its inactivation boosts neutral lipid accumulation under low light. Chapter 5 focuses on ammonium transporters (NgAMT1 and NgAMT2) in nitrogen metabolism, highlighting their roles in ammonium uptake and intracellular trafficking, essential for linking nitrogen availability to lipid metabolism. These findings offer insights into improving Nannochloropsis-based lipid production, to address both environmental and food system sustainability challenges.