Effects of sulfur limitation on nitrogen and sulfur uptake and lipid accumulation in Scenedesmus acuminatus

Sulfur limitation is a frequently exploited method for inducing lipid accumulation in microalgae. However, there is little understanding of the underlying mechanism of this process. Hence, a study was conducted to determine the effects of sulfur limitation on nitrogen and sulfur uptake, lipid production strategies, and photosynthetic physiological characteristics of Scenedesmus acuminatus. A low sulfur concentration (0.076 mM; 0.25S group) decreased nitrate reductase activity and inhibited nitrogen absorption. The highest lipid productivity was obtained in the 0.75S (0.229 mM) group (221.93 mg L−1 day−1), significantly higher than that of the 0.5S (0.153 mM) and 0.25S groups (p < 0.05). Acetyl-coenzyme A carboxylase (ACCase) activity was upregulated in the 0.25S group to promote the accumulation of lipid and fatty acids, and generated the maximum lipid and fatty acid content (47.27% and 43.98% of dry weight, respectively). An important supplementation of energy for lipid accumulation under low-sulfur conditions is to drive a higher proportion of cyclic electron flow. Superoxide dismutase and peroxidase activities and malondialdehyde content increased at lower sulfur concentrations, indicating the elevated antioxidant activity of S. acuminatus.