Transcriptome and key gene expression related to carbon metabolism and fatty acid synthesis of Chlorella vulgaris under a nitrogen starvation and phosphorus repletion regime

For the comprehensive understanding of regulated carbon metabolism associated with lipid accumulation in microalgae Chlorella sp. cultivated with nitrogen starvation and phosphorus repletion (N-P+), the discrepancy among gene expression levels in carbon flow from CO 2 to fatty acid synthesis were characterized through de novo sequencing, transcriptome assembly, annotation, and differential expression analysis. The biomass production of 1900 mg L −1 and lipid content of 677.55 mg (10 10 cells) −1 in Chlorella sp. under N-P+ condition were 1.46-fold and 1.49-fold of those under nitrogen starvation and phosphorus limitation (N-Plim) condition, respectively. The expression levels of many enzymes related to carbon metabolism under N-P+ condition were upregulated, including carbon fixation, pyruvate metabolism, glycolysis, TCA cycle and fatty acid synthesis pathways. CO 2 fixation accelerated through the upregulated Calvin cycle and glycolysis pathways. The rapid synthesis of pyruvate and upregulation of key rate-limiting enzymes involved in fatty acid synthesis favored lipid accumulation.