How Can Algae Food Turn Tetradesmus obliquus into a Mini Nutrient Factory?

Microalgae are emerging as biotech stars, yet only a few generate high biomass yields. A recent study examined the freshwater alga Tetradesmus obliquus to see how nutrient composition affects its growth. Raising ammonium (NH4⁺‑N) to 164 mg L⁻¹ led the alga to produce about 6 g L⁻¹ of biomass with a decent starch content. By fine‑tuning nitrogen, phosphorus and sulfur, productivity nearly doubled, jumping from 0.45 to 0.88 g L⁻¹ day⁻¹. A further increase of ammonium to 410 mg L⁻¹ yielded 7.5 g L⁻¹ of biomass enriched in proteins and pigments. Moreover, the alga removed almost all nitrogen (100 %), 84 % of phosphorus and 96 % of sulfur from the medium. Switching the pH regulator from NaOH to NaHCO₃ did not significantly change growth. These findings demonstrate that, with the right nutrient “recipe,” T. obliquus can act as a mini‑factory of proteins, pigments and other valuable compounds, opening new avenues for sustainable biofuels, food, and cosmetics.

Tetradesmus obliquus belongs to the Chlorophyta class, characterized by a polysaccharide‑rich cell wall and a flexible metabolism. Under photoautotrophic conditions, photosynthesis supplies energy and carbon, while the availability of nitrogen, phosphorus, and sulfur directs carbon flow toward starch, proteins, or pigments. Ammonium is an easily assimilated nitrogen source; at moderate concentrations (≈ 164 mg L⁻¹) it promotes starch synthesis, whereas higher levels (≈ 410 mg L⁻¹) activate protein synthesis pathways, increasing essential amino acid content. Phosphorus, a key component of ATP and nucleic acids, influences rapid cell growth; its limitation shifts metabolic flux toward lipid production, while excess supports cell division. Sulfur is required for sulfur‑containing amino acids (cysteine, methionine) and redox cofactors; near‑complete removal can impair oxidative defense. Using NaHCO₃ as a buffer supplies bicarbonate ions that can be directly incorporated into the Calvin cycle, but in this study it showed no advantage over NaOH, likely because CO₂ levels were already sufficient. These findings indicate that fine‑tuning nutrient concentrations can steer metabolic pathways toward desired products, making T. obliquus a versatile platform for high‑value bioproducts.