Enhanced biosynthesis of high-value compounds in Porphyridium purpureum via nitrogen sources modulation

• Ammonium nitrate reduced CO 2 consumption by up to 6.3-fold through pH self-regulation. • Potassium nitrate significantly boosted exopolysaccharide production (>3 g L⁻ 1 ). • Nitrate-based nitrogen sources enhanced phycoerythrin accumulation during late growth stages. • Ammonium nitrate favored arachidonic acid accumulation, while potassium nitrate increased EPA content. This study evaluates the influence of different nitrogen sources on the growth, photophysiology, phycoerythrin, polysaccharide, and polyunsaturated fatty acids production of the red microalga Porphyridium purpureum . Urea, ammonium nitrate, potassium nitrate, and sodium nitrate were tested as nitrogen sources, revealing significant impacts on pigment accumulation, polysaccharide accumulation, fatty acids composition and carbon dioxide demand. Ammonium-based nitrogen sources reduced CO 2 consumption by up to 6.31 times, making large-scale cultivation more cost-effective. Notably, cultures grown with urea exhibited an atypical yellowish coloration without compromising growth. Furthermore, potassium nitrate significantly enhanced exopolysaccharide production, reaching concentrations above 3 g L⁻ 1 . In terms of arachidonic and eicosapentaenoic acids, the use of ammonium nitrate and potassium nitrate lead advantages. The results of the present study offer valuable insights for optimizing the targeted production of commercially relevant metabolites in P. purpureum , a microalga already cultivated at industrial scale.