Nitrogen And Sulfur Absorption And Lipid Metabolic Characteristics Of Oleaginous Scenedesmus Acuminatus Under Sulfur Deficiency

Scenedesmus acuminatus is a single-celled green alga with growth fast and high lipid production efficiency.In this paper,Scenedesmus acuminatus was used as experimental material,and 0.25S,0.5S and 0.75S were set as different initial sodium sulfate concentration?lower sulfur group?,and modified BG-11?1.0S? was used as control group for 12 days.To explore the response mechanism of carbon and nitrogen metabolism and lipid accumulation in Scenedesmus acuminatus under sulfur deficiency.We analyzing the growth and nitrogen-sulfur absorption characteristics of Scenedesmus acuminatus,the changes of lipids,soluble proteins,carbohydrates and fatty acid components in algae cells under sulfur deficiency.Besides,the changes of reactive oxygen status and antioxidant enzyme activities of Scenedesmus acuminatus were determined under sulfur deficiency.The research results are as follows:?1?Sulfur deficiency have an influnce on the growth of Scenedesmus acuminatus.The cell density of lower sulfur group was significantly lower than that of the control group?p<0.05?,the lowest of 0.25S was 5.58×10⁷cells/mL,and the highest value of 1S was 11.9×10⁷cells/mL.Biomass of the lower group was significantly lower from the 4th day?p<0.05?,the lowest of 0.25S was 3.97 g/L,and the highest of 1.0S was 6.76 g/L.The activity of nitrate reductase?NR?in Scenedesmus acuminatus was positively correlated with the initial sulfur concentration.The nitrate reductase activity of Scenedesmus acuminatus in each concentration group reached the highest on the first day,and the enzyme activity in the 1.0S group was the highest at 6.46 U/g,0.25S group enzyme activity is the smallest,2.50 U/g.Initial sulfur concentration levels affected the absorption of NO₃^- by Scenedesmus acuminatus.From 2th day of culture,the concentration of NO₃^- in the 0.25S and 0.5S groups remained at a high level.The changes of NO₂^- produced in the culture solution under sulfur deficiency was negatively correlated with the initial sulfur nutrition level.NO₂^- in each concentration group?0.25S,0.5S,0.75S,and 1.0S?reached a maximum on day 2,and then decreased sharply.The contents of SO₄^2- in culture medium decreased continuously under different sulfur concentrations.From 2th day of culture,the concentration of SO₄^2- in each concentration group remained basically unchanged,and the 1.0S group was always larger than the low sulfur group.ATPS activity of Scenedesmus acuminatus in the 0.5S group was significantly higher than that in the other groups in the first 2 days before culture?p<0.05?.After 2 days,the enzyme activity in the control group was significant higher than the low sulfur group?0.25S,0.5S??p<0.05?.?2?Lower sulfur promotes the increase of carbon content in cells of Scenedesmus acuminatus,the C/N and N/S values also increased under sulfur deficiency.After 12days of culture,the carbon contents accounted for 60.39% of the dry weight.The carbon accumulation was 45.44 pg/cell.The lipid contents increased with the decrease of sulfur concentration in Scenedesmus acuminatus,of which the total lipid content in 0.25S group reached 47.98% DW.The fatty acid species of Scenedesmus acuminatus are mainly C16:0?palmitic acid?,C16:1?palmitoleic acid?,C16:3?hexadecatrienoic acid?,C18:0?stearic acid?,C18:1?oleic acid?,C18:2?linoleic acid?;The percentage of saturated fatty acid?C16:0? and monounsaturated fatty acid?C18:1? in total fatty acids increased and that of the polyunsaturated fatty acid decreased under lower sulfur group.The initial sulfur concentration was negatively correlated with Acetyl-CoA carboxylase?ACCase?activity of Scenedesmus acuminatus.The ACCase activity of the lower sulfur group was significantly higher than that of the 1.0S group?p<0.05?.It is indicated that the enhancement of ACCase activity of Scenedesmus acuminatus contributes to the accumulation of lipids.?3?The contents of hydroxyl radical?·OH? and malondialdehyde?MDA?in Scenedesmus acuminatus was increased under sulfur stress.They reached the maximum on the 6th day.The contents of ·OH in the 0.25S group was significantly higher than that in the other sulfur concentration groups?p<0.05?.The MDA contents in the lower sulfur group was significantly higher than that in the control group?p<0.05?.With the decrease of sulfur concentration,the SOD and POD activity of Scenedesmus acuminatus increased,reaching the maximum on the 4th day,the activity of SOD and POD in 0.25S group was the highest,and the activity of enzymes in the lower sulfur group was significantly higher than that of the control group?p<0.05?.The above results illustrated that the active oxygen species was increased and the antioxidant enzyme activity was enhanced under sulfur deficiency in Scenedesmus acuminatus.