Two-stage cultivation of Scenedesmus acuminatus with nitrogen and sulfur for growth and lipid accumulation

In this work two-stage cultivation of Scenedesmus acuminatus to enhance lipid productivity was investigated. Two two-stage cultivation strategies were employed: 1) S . acuminatus was cultured in nitrogen-limited conditions (0.75 g L −1 NaNO 3 , stage I), then nitrogen-limited condition (stage II); 2) S . acuminatus was cultured in sulfur-replete conditions (86.80 g L −1 MgSO 4 , stage I), then nitrogen-limited conditions (stage II). The lengths of stages I and II were varied within a total culture period of 20 days. The highest biomass (12.41 g L −1 ) and lipid productivity (346.51 mg L −1 day −1 ) were obtained when stage I lasted 8 days and the cells were then transferred to medium containing 0.3 g L −1 NaNO 3 (stage II) for another 12 days; these values were 1.72- and 2.18- times higher, respectively, than those for the control group (single-stage cultivation in control group, 1.5 g L −1 NaNO 3 ). Biochemical analyses indicated that S . acuminatus produced higher biomass and lipid content if stable carbon partitioning model occurred in stage II of culture. Overproduction of carbohydrates or soluble protein after transfer to the second stage was not conducive to the optimal balance of cell growth and lipid content. The findings of this study indicate that the regulation of nitrogen concentration to promote lipid accumulation is more effective than regulation via the sulfur concentration. This two-stage cultivation process is of interest for large-scale cultivation of S . acuminatus for enhanced lipid accumulation.