Effects of initial combined concentrations of nutrients on the growth and lipid accumulation of Eustigmatos cf. polyphem

To determine the effects of different initial combined concentrations of N, P and S on the growth, lipid accumulation, and fatty acid compositions of Eustigmatos cf. polyphem D. J. Hibberd, we cultivated the algae in modified BG-11 medium containing different combined concentrations of nutrients (sodium nitrate, dipotassium phosphate, and magnesium sulfate used as nitrogen (N), phosphorus (P), and sulfur (S) sources, respectively). Biomass concentration, total lipid content, fatty acid composition, and primary intracellular nutrient element content were measured by dry weight, gravimetrics, gas chromatography, and elemental analyzer, respectively. Results showed that different initial combinations of N, P, and S significantly affected the growth, lipid accumulation, and fatty acid composition of E. cf. polyphem. The highest biomass concentration reached 9.19 g/L under 9 mmol/L NaNO₃, 0.92 mmol/L K₂HPO₄, and 0.3 mmol/L MgSO₄. Low N or P stress or combined low N and P stress promoted lipid accumulation, though there was no obvious influence on lipid accumulation under low S stress. The highest total lipid content reached 68.7% of dry weight under 3 mmol/L NaNO₃, 0.029 mmol/L K₂HPO₄, and 0.3 mmol/L MgSO₄. The E.cf.polyphem fatty acids were rich in palmitoleic acid, with relative amounts reaching 60.88% of total fatty acid. Thus, reasonable combined concentrations of N, P, and S effectively promoted growth and lipid and palmitoleic acid accumulation of E. cf. polyphem.