Influence of Nutrient Medium Composition on the Redistribution of Valuable Metabolites in the Freshwater Green Alga Tetradesmus obliquus (Chlorophyta) Under Photoautotrophic Growth Conditions

The study of microalgae has led to significant progress in recent decades. The current microalgal biomass yield is unsatisfactory, except for certain species that are cultivated for the nutraceutical and pharmaceutical industries. In this study, the growth efficiency and biochemical composition of <i>Tetradesmus obliquus</i> at high levels of nutrients were characterized. Increasing the NH₄⁺-N content in the medium to 164 mg L^-1 allowed the algae to steadily accumulate biomass (6.14 ± 0.28 g L^-1) with a moderate content of starch. Optimizing the levels of N, P, and S allowed the biomass productivity to increase from the average 0.45 to 0.88 g L^-1 day^-1. A further increase of NH₄⁺-N to 410 mg L^-1 and other nutrients' concentration allowed the algae to accumulate biomass (7.50 ± 0.28 g L^-1), enriched with protein and pigments. The algae cultivated with the high load of nutrients reached 100%, 84%, and 96% removal of N, P, and S, respectively. Adding the NaHCO₃ to the photobioreactor for pH adjustment (instead of NaOH) did not significantly improve the growth parameters or affect the composition of the algal cells. In general, our study will improve the comprehensive understanding of culture-based approaches to study the perspective use of the alga <i>T. obliquus</i>.