Beyond Phaeodactylum tricornutum: Comparative evaluation of freshwater diatoms for nutrient removal, bioproduct potential and physiological responses

Diatoms are microalgae that have significant potential in sustainable biorefineries, combining nutrient removal capabilities with the production of high-value biomolecules. While the marine Phaeodactylum tricornutum has been extensively characterized, the performance of common freshwater species in comparable applications remains rather unexplored. This study compares the nutrient removal efficiency, lipid and pigment yields, and physiological responses of P. tricornutum and two freshwater diatom species -Achnanthidium saprophilum and Planothidium frequentissimum- under controlled conditions and varying nitrate concentrations. The results reveal that both P. tricornutum and P. frequentissimum exhibit competitive nutrient uptake rates, achieving over 95% nitrate removal efficiency. P. frequentissimum exhibits significant lipid and pigment production. Lipid production in this species is up to six times higher than in P. tricornutum, and total pigment production is up to ten times higher. Nevertheless, P. tricornutum doubles the growth rate of the other two species. Physiological analyses indicate reduced photosynthetic activity under nitrate-limited conditions. Notably, A. saprophilum shows tolerance to nitrate depletion, whereas P. frequentissimum is strongly affected. These findings highlight the untapped potential of freshwater diatoms for bioremediation applications and broaden the foundation for sustainable biotechnology research.