Effects of sulfate ions on growth and lipid synthesis of Scenedesmus obliquus in synthetic wastewater with various carbon-to-nitrogen ratios altered by different ammonium and nitrate additions

Abstract

Producing biodiesel from microalgae is a promising strategy to upgrade energy structure. In this study, effects of sulfate (SO₄^2-) on lipid synthesis of Scenedesmus obliquus (S. obliquus) cultivated in synthetic wastewater with different carbon to nitrogen (C/N) ratios regulated by ammonium (NH₄⁺-N) and nitrate (NO₃^--N), separately, were investigated. The results shown that SO₄^2- could dramatically increase cell growth preferring to NH₄⁺-N supply. And SO₄^2- addition could improve its carbon and nitrogen utilization potential for boosting lipid productivity leading α-linolenic acid (C18:3n3) to occupy a dominant component (38.96%) in NH₄⁺-N group at a C/N ratio of 7.5. Additionally, SO₄^2- could enhance the enrichment and expression of up-regulated genes annotated in key enzymes such as GK, GNPAT, CRLS, plc and DEGS involved in glycerolipid, glycerophospholipid and sphingolipid metabolic pathways, resulting in carbon metabolism enhancement and sulfatide accumulation. This study brings a comprehensive view towards nutritional regulation of lipid synthesis in microalgae.

Keywords: Carbon to nitrogen (C/N) ratio; Lipid accumulation; Scenedesmus obliquus; Sulfate; Transcriptome.