Transcriptomic and physiological insights into Diethylstilbestrol toxicity in Phaeodactylum tricornutum

Diethylstilbestrol (DES), an emerging pollutant, poses a threat to marine ecosystems, but its toxic effects on marine phytoplankton and the underlying mechanisms are not well understood. To address this knowledge gap, this study systematically investigated the physiological and molecular responses of the marine diatom Phaeodactylum tricornutum to DES exposure, aiming to uncover its toxicological mechanisms. DES significantly reduced chlorophyll content and photosynthetic efficiency, impaired the PSII core, and decreased both photosynthesis and respiration rates. The diatom responded by enhancing antioxidant defenses, including superoxide dismutase and catalase activities. DES was also partially removed from the water column, with removal rates of 9-18 %. Transcriptomic analysis revealed extensive changes in genes involved in porphyrin metabolism and carbon fixation, which were closely linked to the observed physiological impairments. In summary, these findings reveal a core toxicological mechanism whereby DES disrupts photosynthesis through inhibition of carbon fixation and porphyrin metabolism, providing new insights into how emerging pollutants impair marine primary producers and offering a scientific basis for the ecological risk assessment of DES contamination.