Salinity driven stress to enhance lipid production in Scenedesmus vacuolatus: A biodiesel trigger?

The main aim of the present study is to understand algae behaviour and enhancement of the intracellular neutral lipid content of freshwater green microalgae, Scenedesmus vacuolatus, under salt exposure. Effects of various salts (sodium chloride, magnesium chloride and calcium chloride) on this species were analysed by measuring parameters such as growth rate, chlorophyll content, neutral lipid intensity and conducting FAME profiling. When under stress, microalgae divert their metabolic pathways towards lipid synthesis, and this is evidenced in the current study. Compared to controlled and unmodified media cultivation, sodium chloride and magnesium chloride exposure promoted 383% and 340% higher fluorescence intensities, respectively, and there was a significant increase in the FAME content, particularly of saturated fatty acids (such as palmitic and stearic acid) at a magnesium chloride concentration of 50 mM and calcium chloride exposure of 70 mM, with percentage increases of 109% and 253%, respectively, compared to the control. Algal cells were found to be more tolerant towards NaCl than other salts, and this was confirmed through the biomass accumulation profile. Biomass productivity was highest at exposure to 100 mM sodium chloride (33 mgL−1d−1) followed by calcium chloride (19.5 mgL−1d−1) and magnesium chloride (12.6 mgL−1d−1). Confocal imaging further supported the results, and scanning electron microscopy revealed changes in algal surface morphology. This study provides further information about stress-driven lipid biosynthesis and analyses changes in cellular morphology and physiology. However, further exploration and systematically studies are required to determine exact mechanism involved in neutral lipid enhancement inside cells and associated metabolomics.