Growth, biochemical composition, and photosynthetic performance of Scenedesmus acuminatus during nitrogen starvation and resupply

Many microalgae store energy as triacylglycerols under certain environmental conditions. Nitrogen limitation is recognized as an efficient lipid-accumulation trigger in microalgae. Here, biochemical composition (lipids, carbohydrates, and soluble proteins) time courses, fatty acid composition, pigment accumulation, and the photosynthetic efficiency of photosystem II (PSII) in Scenedesmus acuminatus were investigated under nitrogen starvation and resupply conditions. This work provides a theoretical basis for how microalgae utilize nitrogen to optimize lipid production. Nitrogen starvation inhibits cell division and growth, and promote the accumulation of lipids and carbohydrates. The total lipid content under nitrogen starvation approached 50.12% of the dry weight and neutral lipids accounted for 92.55% of the total lipids. Upon NaNO3 supplementation at day 9, the maximum photosynthesis efficiency (F-v/F-m), and the total amino acid, soluble protein, and pigment levels recovered rapidly within the first 12 h, while the degraded carbohydrate served as a carbon and energy source. After a 2-day lag time (from days 9 to 11), the biomass increased rapidly. The biomass concentration and lipid content reached 4.24 g L-1 and 36.46% of dry weight, respectively, at the end of cultivation. The Chla and Chlb contents of S. acuminatus were more sensitive than the carotenoid content to environmental nitrogen sources. The change in non-photochemical quenching (NPQ) was complicated, significantly increasing to a peak and then decreasing during both nitrogen starvation and recovery.