Elevated CO 2 improves lipid accumulation by increasing carbon metabolism in Chlorella sorokiniana

Summary Supplying microalgae with extra CO 2 is a promising means for improving lipid production. The molecular mechanisms involved in lipid accumulation under conditions of elevated CO 2, however, remain to be fully elucidated. To understand how elevated CO 2 improves lipid production , we performed sequencing of Chlorella sorokiniana LS ‐2 cellular transcripts during growth and compared transcriptional dynamics of genes involved in carbon flow from CO 2 to triacylglycerol. These analyses identified the majority genes of carbohydrate metabolism and lipid biosynthesis pathways in C. sorokiniana LS ‐2. Under high doses of CO 2 , despite down‐regulation of most de novo fatty acid biosynthesis genes, genes involved in carbohydrate metabolic pathways including carbon fixation, chloroplastic glycolysis, components of the pyruvate dehydrogenase complex ( PDHC ) and chloroplastic membrane transporters were upexpressed at the prolonged lipid accumulation phase. The data indicate that lipid production is largely independent of de novo fatty acid synthesis. Elevated CO 2 might push cells to channel photosynthetic carbon precursors into fatty acid synthesis pathways, resulting in an increase of overall triacylglycerol generation. In support of this notion, genes involved in triacylglycerol biosynthesis were substantially up‐regulated. Thus, elevated CO 2 may influence regulatory dynamics and result in increased carbon flow to triacylglycerol, thereby providing a feasible approach to increase lipid production in microalgae.