Scenedesmus acutus extracellular polysaccharides produced under increased concentration of sulphur and phosphorus exhibited enhanced proliferation of peripheral blood mononuclear cells

Exopolysaccharides (EPS) isolated from microalgae are promising immune cell proliferation agents, that could be potentially used as immunostimulants. In the current study, Scenedesmus acutus (S. acutus) was grown under varying nutrient (sulphur and phosphorus) concentrations to enhance the EPS production, and the isolated EPS were assessed for their effect on cell proliferation using peripheral blood mononuclear cells (PBMC). Five different concentrations of MgSO₄ (0, 0.25, 0.5, 1.0 and 1.25 g/L) and K₂HPO₄ (0, 0.2, 0.6, 0.8 and 1.0 g/L) were taken as compared to the normal culture conditions (0.75 g/L MgSO₄ and 0.4 g/L K₂HPO₄) with the intention to enrich EPS secretion. LC–MS, FTIR and NMR analysis revealed that isolated EPS have the characteristic spectrum of hetero-polysaccharides (octa-saccharides). Immunostimulatory property of EPS was demonstrated by their ability to augment PBMC proliferation as measured by MTT assay. Further, increase in the glucose content and proliferative index was observed for EPS obtained under higher concentrations of MgSO₄ (1 and 1.25 g/L) and K₂HPO₄ (0.6 and 0.8 g/L) relative to normal culture conditions. Effects of the generated EPS under varying concentration of MgSO₄ (r = 0.84–0.99) and K₂HPO₄ (r = 0.76–0.97) remained strongly correlated with cell count, chlorophyll content, total biomass, glucose, proliferative index and its scavenging activity. Collectively, our data not only showed that EPS generated by S. acutus under higher concentration of K₂HPO₄ and MgSO₄ possess improved immunostimulatory properties, but also provides convincing evidence towards nutritional optimization of alga for enhanced EPS production with better bioactivities.