Abstract
Nitrogen deprivation (−N) has been used as a technique to promote lipid accumulation in various microalgae. Scenedesmus acutus is a promising oleaginous green microalga that can be cultivated in organic wastewater for biodiesel production. Nevertheless, the molecular mechanisms controlling S. acutus lipid accumulation in response to −N remain unidentified. Physiological study determined that −N reduced cell growth and photosynthetic pigments. On the other hand, it promoted carbohydrate and neutral lipid accumulation. To find the mechanisms underlying lipid accumulation, we performed de novo transcriptome profiling of the non-model S. acutus in response to −N. The transcriptome analysis revealed that glycolysis and starch degradation were up-regulated; on the contrary, gluconeogenesis, photosynthesis, triacylglycerol (TAG) degradation and starch synthesis were down-regulated by −N. Under −N, the carbon flux was shifted toward fatty acid and TAG synthesis, and the down regulation of TAG lipase genes may contribute to TAG accumulation. A comparative analysis of the −N transcriptomes of oleaginous microalgae identified that the down-regulation of multiple lipase genes was a specific mechanism found only in the −N transcriptome of S. acutus. Our study unraveled the mechanisms controlling −N-induced lipid accumulation in S. acutus, and provided new perspectives for the genetic manipulation of biodiesel-producing microalgae.
Highlights
Higher economic growth is positively associated with an increase in petroleum consumption
We found that the expression of phosphofructokinase (PFK: c6362_g1_i1 and c10466_g19_i1 and i2), glyceraldehyde 3-phosphate dehydrogenase (GAPDH: c10641_g1_i1 and c24212_g1_i1), phosphoglycerate mutase (PGAM: c3021_g1_i2, c9255_g2_i1, c10485_g24_i3, and c24459_g1_i1), enolase (c19909_g1_i1 and c29129_g1_i1), and pyruvate kinase (PK: c4713_g2_i1, c10123_g12_i1, c10306_g22_i1, and c19619_g1_i1) was induced under −N (Fig. 5; Supplementary Table 1)
Our analysis found that the genes involved in amino acid and nucleotide metabolism were over-represented in the up-regulated differentially expressed genes (DEGs) in S. acutus and N. oceanica
Summary
Higher economic growth is positively associated with an increase in petroleum consumption. Microalgae are well-known as a potential source for biodiesel production. They are efficient oxygenic photosynthetic organisms that are easy to cultivate and are fast growing. Scenedesmus acutus is a fresh-water oleaginous microalga that has a high potential for biodiesel application due to its ability to grow in organic wastewater and to accumulate high lipid content[10,11]. Studies in model oleaginous microalgae, including C. reinhardtii and Nannochloropsis oceanica, revealed that −N-induced lipid accumulation can cause extreme alterations at the transcriptomic, proteomic, and metabolomic levels[5,6,8,13,14,15,16]. De novo transcriptome analysis, in combination with gene expression profiling, could provide a basic understanding of the molecular responses to −N-induced lipid accumulation in a non-model S. acutus
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