Improvement in biochemical parameters and changes in lipid profile of Scenedesmus obliquus by plant growth regulators under mixotrophic condition

Abstract

In this study, we investigated the improvement in biochemical parameters by adding gibberellic acid (GA3) and salicylic acid to mixotrophy medium. Fresh weight of the cultures treated with 100 mM SA and GA3 was approximately 30% higher than that of control cultures. Both GA3 and SA induced chlorophyll, carotenoid, and astaxanthin accumulation in Scenedesmus. SA increased carotenoid and astaxanthin content 2 and 2.6 times more than GA3 respectively. Protein content decreased in microalgae treated by GA3 and SA. 100 mM concentration of GA3 and SA caused a significant increase in lipid levels (42.6% and 41%, respectively). Compared with the controls, lower proportions of unsaturated fatty acids (USFAs) were detected in the GA3-and SA-treated biomass. In the microalgae treated by GA3, an insignificant decrease was detected in saturated fatty acids (SFA) and USFAs in comparison to the controls. New fatty acids, SFA C16:0 (2.5%), and USFA C22:6 (n3) (docosahexaenoic (DHA) (2.1%) were added to the fatty acid profile. Adding SA to the microalgal cultures significantly increased the amount of SFAs and reduced the amount of USFAs compared to the controls. 21.2% C8:0 and 29.4% EPA had the highest content in SFAs and USFAs, respectively. Our results showed that GA3 and SA (especially SA) can be good candidates for improving carotenoid and astaxanthine under mixotrophy conditions and changing the amount of special fatty acids.