Abstract
Cadmium (Cd), a toxic heavy metal, poses a significant threat to aquatic ecosystems by impairing primary producers such as microalgae. This study investigated the adaptive responses of Chlamydomonas reinhardtii to Cd stress through physiological, biochemical, and GC-MS-based lipidomic analysis. Cultures were exposed to the EC50 concentration of Cd (20 ppm) for 8 days. Cd exposure significantly increased oxidative stress markers, including hydrogen peroxide (+69%), malondialdehyde (+336%), and proline (+144%). Total carbohydrate and lipid contents increased by 21.7% and 14%, respectively, whereas protein and total photosynthetic pigment contents decreased by 39.5% and 44%, respectively, indicating metabolic reprogramming under Cd stress. Antioxidant capacity was enhanced as reflected by a 50% reduction in the DPPH IC50 value. Lipidomic analysis revealed a decrease in unsaturated fatty acids accompanied by the accumulation of lipid-derived aldehydes and saturated hydrocarbons. KEGG pathway enrichment analysis identified significant alterations in fatty acid biosynthesis, fatty acid elongation, glutathione metabolism, and butanoate metabolism, highlighting coordinated oxidative and lipid metabolic reprogramming as key adaptive responses to Cd stress.