Multifaceted stress response in Tetradesmus obliquus to selenium dioxide exposure: antioxidant defense and metabolic...

This study investigated the effects of SeO₂ at concentrations of 0, 25, 50, 75, and 100 mg L⁻¹ on the microalgae Tetradesmus obliquus over seven days. Lower concentrations (25 and 50 mg L⁻¹) promoted algal growth and maintained photosynthetic pigments. In contrast, higher concentrations (75 and 100 mg L⁻¹) caused growth rate decreases of 20.13% and 41.35%, respectively, along with reductions in chlorophyll a (Chl a) content (26.36% and 65.01%). Elevated SeO₂ levels also increased activities of antioxidant enzymes such as ascorbate peroxidase (APX) and polyphenol oxidase (PPO), as well as carotenoid accumulation, indicating activation of stress responses. Notably, starch content increased by 180% at 100 mg L⁻¹, while soluble sugar levels decreased, suggesting a shift in carbon metabolism. Amino acid analysis revealed significant changes, including increases in glutamic acid (224.3%), lysine (135%), and cysteine (30%), and decreases in alanine (94%), valine (86%), tyrosine (27%), methionine (20.54%), arginine (54.2%), and asparagine (58%) under 100 mg L⁻¹ SeO₂ exposure. These biochemical alterations were associated with oxidative stress markers and reduced photosynthetic efficiency. Overall, SeO₂ exhibits a concentration-dependent dual effect, highlighting T. obliquus as a promising bioindicator for selenium (Se) contamination and a potential resource for biotechnological applications.