Nitrate stress-induced bioactive sulfated polysaccharides from Chlamydomonas reinhardtii

Sulfated polysaccharides (SPs) are anionic carbohydrate polymers synthesized as extracellular or cell wall components by most of the algae and have potent bioactive properties. In the current study, Chlamydomonas reinhardtii (Cr) cells were attributed to sodium nitrate stress in concentrations such as 5 mM, 10 mM, 20 mM, 30 mM, and a control to determine the productivity and bioactivity of SPs. SPs are extracted by hot water method using 80% ethanol. The percentage yield of SPs increased with an increase in concentration of sodium nitrate as compared to control. Biochemical analysis of the extract showed an increase in carbohydrate content (22%–95%), uronic acid content (23%–60%), and sulfate content from control to 30 mM NaNO3-treated extracts. The amount of reducing and nonreducing sugars was found to be 6.16% and 89.06%, respectively, while the protein content is ~16%. The antioxidant potential of SPs showed increased antioxidant activity with an increase in concentration of NaNO3 stress. The analysis resulted in maximum chelating activity of 83.73% assayed in concentration range of 1–8 μg/ml, total antioxidant activity of 70.36% in concentration 0.05–2μg/ml, and hydroxyl radical scavenging activity of 79.52% in concentration 250–1000 μg/ml; reducing potential was observed with the highest absorbance of 0.87; the 2,2-diphenyl-1-picrylhydrazyl scavenging activity showed the highest activity of 63.61%, while the superoxide scavenging activity was 92% at 0.1–1 μg/ml. Furthermore, Cr-SPs inhibited the growth of Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli bacterial growth as indicated by clear zones that increased in size with an increasing concentration of NaNO3. These results provide opportunities to develop Cr-SPs as natural antioxidant and antibacterial agents.