Metabolic Network Reconstruction And Metabolic Pathway Analysis For Enhanced Triacylglycerol Production Of Chlorella

Algal triacylglycerol(TAG) can be used to produce biodiesel, which is one of the promising alternatives to fossil fuel. In order to produce algal biodiesel effectively, the production of algal TAG can be enhanced by genetic engineering. To effectively enhance TAG productivity by genetic engineering, it is necessary to analyze the metabolic network and find key reactions.In this work, the central metabolic networks of algae with TAG producing process under three different cultivation conditions, namely heterotrophic, photoautotrophic-fermentation condition (PFM) and autotrophic condition are first reconstructed from annotated genome data. Elementary flux mode (EM) analysis and two EM-analysis based computational methods, namely CASOP (Computational approach for strain optimization aiming at high productivity) and modified CASOP are then used to evaluate the importance and genetic modification potential of reactions. EM analysis identifies possible genetic engineering targets by comparing ideal TAG-producing and biomass-producing metabolic flux pathways. CASOP evaluates the possibility of a reaction to be a genetic engineering target by analyzing the amount and yield of metabolic pathways the reaction participates in, while the modified method also takes reaction rate into consideration.The results show that Kennedy pathway and fatty acid synthesis reactions are of high importance regardless of conditions. NADPH producing reactions are of high importance in the heterotrophic condition, whereas light reactions in the autotrophic network are important as the major source of energy. The existence of glyceraldehyde3-phosphate dehydrogenase (NADP+) under PFM condition and malic enzyme under autotrophic condition may enhance the production of lipid by forming a transhydrogenase-like cycle, offering an effective pathway of NADPH production. The results also partly explains how environmental stress trigger TAG accumulation. The results of this analysis provide new insight and possible targets for algae genetic engineering.