13C-metabolic flux analysis of lipid accumulation in the green microalgae Tetradesmus obliquus under nitrogen deficiency stress

Metabolic fluxes (MF) serve as the functional phenotypes of biochemical processes and are crucial to describe the distribution of precursors within metabolic networks. There is a lack of experimental observations for carbon flux towards lipids, which is important for biodiesel generation. Here, the accumulation of lipid, and MF in Tetradesmus obliquus under nitrogen deficiency stress (NF) using a 13C isotope tracer at different time intervals was investigated. The 13C based MF showed enhanced de novo synthesis of G3P and PEP, indicating increased carbon flux from CO2 into lipid synthesis. An increase in palmitic acid (3500 μmol/mg), linoleic acid (2100 μmol/mg), and oleic acid (2000 μmol/mg) was observed. The accumulation of C16:0 under NF was mainly related to de novo synthesis while C18:3 was accumulated through a non de novo pathway. Under NF stress, T. obliquus had higher flux in PPP and glycolysis pathway, together, it might provide more NADPH and substrate acetyl-CoA for fatty acid synthesis.