Optimizing nitrogen source and concentration for enhanced biomass and bioproducts in Scenedesmus dimorphus

Microalgae are photosynthetic unicellular microorganisms with high biomass productivity and potential for producing value-added compounds such as pigments, proteins, lipids, and carbohydrates. Scenedesmus dimorphus has been extensively studied for biodiesel produc-tion and biotechnological applications; its biochemical composition is influenced by nitrogen source and concentration. This study investigates the effects of ammonium and nitrate (1, 2, 4, 8, 16 mM) on biomass productivity and macromolecule accumulation in S. dimorphus, cultivated in 450 mL photobioreactors using modified BG11 medium. Results indicate that ammonium had an inhibitory effect on S. dimorphus at all tested concentrations, whereas all nitrate concentrations supported growth, with the highest biomass productivity at 4 mM. Protein and carbohydrate productivity peaked at 8 mM, while lipid accumulation was highest at 1 mM. Additionally, nitrate concentrations between 1 and 4 mM increased polyunsatu-rated fatty acid content and reduced chain length. Despite these variations, all cultures yielded lipids suitable for biodiesel production. Selecting nitrate concentration based on tar-get products could reduce nitrogen input costs by 55-94%, improving the economic feasibil-ity of large-scale S. dimorphus cultivation.