Effect of Nitrogen Limitation on Growth, Biochemical Composition and Cell Ultrastructure of the Microalga Picocystis Salinarum

Abstract In recent years, biodiesel production has attracted worldwide attention due to the awareness of fossil fuel depletion, and microalgae biomass is considered a promising raw material for its formulation. The present study evaluated the effects of different levels of nitrogen limitation (37.5, 18.75, 9.375 mg L-1 NaNO3) on the growth, cell ultrastructure and biochemical composition of Picocystis salinarum as a potential raw material source for biodiesel. During a culture period of 20 days, the growth measurements were estimated, and cell density, dry weight and chlorophylls a, b content decreased with time as nitrogen limitation increase, however, carotenoids content increased. The high N limitation (9.375 mg L-1) had a highly significant effect on the accumulation of total lipid content (33.87% dry weight), carbohydrate content increase (30.98% dry weight), but protein content decrease (1.89% dry weight). The lipid content showed a differential FAME profile with high saturated fatty acid values (996.08 µg g-1 dry weight) mainly C16:0, compare with the unsaturated ones that showed low values under high N limitation. The gradual increase of lipid content was also corroborated by transmission electron microscopy images with lipid droplet cell formation. Therefore, evaluation of the algal culture conditions such as N limitation, as a strategy to maximize lipid content and improve the fatty acid profile in unexplored halophilic P. salinarum showed a potential biomass yield as a suitable candidate for biodiesel production.