Effects of nitrogen starvation on TAG biosynthesis genes expression in Chlorella vulgaris

Abstract

Microalgal oils and lipids are the potential sources of sustainable industrial products for pharmaceuticals, nutraceuticals, and cosmeceuticals. However, the production cost of microalgal-based products is still expensive and hinders their marketability. Therefore, research has been focusing on increasing microalgae's oil and lipids content to be economically reasonable. Nutrient stresses were often used to enhance oils and lipids production in microalgae. In this study, the microalga Chlorella vulgaris was exposed to nitrogen starvation for 21 days to examine the effect of nitrogen removal on cell density, total oil content, fatty acids composition, and the expression of two triacylglycerols (TAG) biosynthetic genes, glycerol-3-phosphate acyltransferase (GPAT) and diacylglycerol acyltransferase (DGAT). The results showed that the C. vulgaris cells grew extremely slowly (p<0.05) under nitrogen starvation conditions. However, despite the growth outcome, the nitrogen starvation increased (p<0.05) total oil contents on days 3, 11 and 14 relatives to control. Nitrogen starvation also stimulated (p<0.05) the production of saturated fatty acids (SFA). The primary fatty acids detected were C16:0, C18:0, C18:1, C18:2, C18:3 and C20:0. The effect of nitrogen starvation on the expression of TAG biosynthetic genes, GPAT and DGAT genes were enumerated using real-time PCR. Both GPAT and DGAT were downregulated in this study. Interestingly, the buildup of C18:2 and C18:3 was positively linked with GPAT expression, demonstrating that GPAT affected the synthesis of polyunsaturated fatty acids (PUFA) in nitrogen-starved circumstances. This suggests that the GPAT gene may be altered to increase PUFA in microalgae, notably C18:2 and C18:3.