Engineering of lipid metabolism in the microalgae Nannochloropsis gaditana

The exponential growth of the world population is causing an increased demand for energy and food that cannot be supported by current agricultural yields. Furthermore, intensive agriculture is the cause of strong environmental impacts, leading to soil degradation, loss of ecosystems and biodiversity. In this context, microalgae industrial cultivations will play a fundamental role in reducing the impacts of climate change and developing a more sustainable economy. Among known microalgae, Nannochloropsis have attracted considerable attention due to their ability to accumulate a large fraction of reduced carbon as lipids. This master’s thesis deals with the comprehension of microalgae lipid metabolism, with a particular focus on enhancing lipid accumulation in Nannochloropsis gaditana. The central hypothesis driving this research is that modulation of a triose phosphate translocator (TPT) activity can lead to an increase in the cytosolic lipid content in specific growth conditions, because the principal triose phosphate molecule transported by this transporter is dihydroxyacetone phosphate (DHAP) that is also an essential molecule in the metabolism, being an intermediate in various metabolic pathways. Through transcriptomic analysis, four genes encoding TPTs were previously identified in Nannochloropsis gaditana but only one of these transporters exhibit significant homology with an Apicomplexan-like DHAP transporter, which suggests a potential opposite role in lipid metabolism, importing DHAP from the cytosol to the chloroplast. To better understand the role of this transporter in the cell carbon partitioning, we used knockout mutants generated by CRISPR-Cas technology. A series of growth curve experiments were conducted to assess the impact of transporter disruption on neutral lipid accumulation. Our findings demonstrate that the TPT knockout mutants exhibit a significant increase in lipid accumulation compared to the wild type in the tested light condition. This research not only contributes to our understanding of microalgae lipid metabolism, but also presents a promising starting point for enhancing lipid production through targeted genetic modifications. As a side project, we used an optimized strain of Nannochloropsis oceanica (IMET1) to obtain a mutant with the aim to overexpress a specific fatty acid desaturase (ω3 FAD) involved in converting ω-6 fatty acids to ω-3 fatty acids to improve the fatty acid profile and the ω3/ω6 ratio enhancing its nutritional value and health benefits.