Response mechanism of Chlamydomonas reinhardtii to nanoscale bismuth oxyiodide(nano-BiOI):Integrating analysis of mineral nutrient metabolism and metabolomics

Nanoscale bismuth oxyiodide(nano-BiOI) is widely studied and applied in environmental applications and biomedical fields, with the consequence that it may be deposited into aquatic environments. However, the impact of nano-Bi OI on aquatic ecosystems, especially freshwater microalga, remains limited. Herein, the nano-Bi OI was synthesized and its response mechanism towards microalga Chlamydomonas reinhardtii was evaluated. Results showed that a low concentration of nano-Bi OI(5 mg/L) could stimulate algal growth at the early stage of stress. With the increase in concentration, the growth rate of algal cells was inhibited and showed a dose effect. Intracellular reactive oxygen species(ROS) were significantly induced and accompanied by enhanced lipid peroxidation, decreased nonspecific esterase activity, and significantly upregulated glutathione S-transferase activity(GST) activity. Mineral nutrient metabolism analysis showed that nano-Bi OI significantly interfered with the mineral nutrients of the algae. Non-targeted metabolomics identified 35 different metabolites(DEMs, 22 upregulated, and 13 downregulated) under 100 mg/L Bi OI stress.Metabolic pathway analysis demonstrated that a high concentration of nano-Bi OI significantly induced metabolic pathways related to amino acid biosynthesis, lipid biosynthesis,and glutathione biosynthesis, and significantly inhibited the sterol biosynthesis pathway.This finding will contribute to understanding the toxicological mechanisms of nano-Bi OI on C. reinhardtii.