The microalga Scenedesmus quadricauda mitigates 17α-ethynylestradiol toxicity via enhanced photosynthesis and...

The freshwater microalga Scenedesmus quadricauda, a crucial primary producer, demonstrates significant capacity to biodegrade new pollutants. While its ability to remove synthetic estrogen 17α-ethynylestradiol (EE2) is recognized, the underlying physiological and molecular mechanisms facilitating this tolerance remain poorly defined. This study elucidates the key adaptive responses of S. quadricauda to EE2 exposure by integrating growth analyses, physiological assays, and transcriptomic profiling. EE2 initially inhibited algal growth, inducing oxidative stress and disrupting processes related to ribosome and RNA synthesis. However, this inhibition was alleviated over time through the activation of two primary defense systems. First, the antioxidant defense system (SOD, GSH-Px) was significantly upregulated. Second, photosynthetic efficiency was enhanced to meet the elevated energy demands of detoxification. Concurrently, the upregulation of ABC transporters suggested improved cellular efflux of EE2 or its metabolites. These findings identify enhanced photosynthesis and antioxidant capacity as critical physiological biomarkers of EE2 stress mitigation in microalgae.