Impact of pH, nutrient, and salinity stress on lipid synthesis in Coelastrella sp. for sustainable biodiesel production

The study examined the lipid production potential of the freshwater microalga Coelastrella sp., isolated from a pond in Gundur, Tiruchirappalli, Tamil Nadu, India. The alga was cultured in BG-11 medium under different conditions of pH, salinity, and nutrient availability to optimize lipid yield. The cultures were incubated at 25 °C with constant illumination (3000 lx) and aeration for a period of three weeks. The effects of pH levels (6.0, 7.0, 8.0, 9.0), sodium chloride concentrations (0.2 mM to 0.8 mM), sodium nitrate levels (2 mM to 8 mM), and inorganic fertilizer concentrations (0.05% to 2.0%) on biomass and lipid productivity were assessed. The highest biomass productivity (0.199 g/L/day) and lipid productivity (0.108 g/L/day) were observed at pH 7.0, with nitrate concentrations of 0.4 mM yielding the most significant total lipid content (0.102 g/L/day). Optimal salinity was found at 0.8 mM, and fertilizer concentration of 0.5% significantly enhanced biomass and lipid yields, achieving a biomass productivity of 0.200 g/L/day and lipid productivity of 0.115 mg/L. Key findings included increased lipid accumulation under stress conditions, as indicated by Nile Red staining. FTIR analysis revealed the presence of functional groups linked to triacylglycerides (TAGs) and other lipids. Gas chromatography identified noteworthy fatty acids, such as linolelaidic acid (24%), cis-11,14-eicosadienoic acid (17%), and arachidonic acid (11%). Despite the presence of polyunsaturated fatty acids (PUFAs), particularly C18:2, C18:3, and C20:4, which are valuable for nutraceutical and pharmaceutical applications, the study identified fatty acid profile with monounsaturated (MUFA) and saturated fatty acids (SFA) that make Coelastrella sp. a promising candidate for biodiesel production.