The toxicity of microplastics (MPs) to marine microalgae has raised much concern. However, research at metabolic level is quite limited. In this study, the physiological and metabolic effects of polystyrene (PS) and aged polystyrene (A-PS) MPs on Dunaliella salina were investigated. Both PS and A-PS inhibited the growth of microalgae, but promoted the pigment synthesis in algal cells. The oxidative stress analysis indicated that PS and A-PS induced high production of reactive oxygen species (ROS), and caused oxidative damage to algal cells. Particularly, the highest ROS level in PS and A-PS groups were 1.70- and 2.24-fold of that in the control group, respectively. Untargeted metabolomics analysis indicated that PS and A-PS significantly increased the differential metabolites. Compared with the control group, the significant upregulation of glycerophospholipids metabolites illustrated that severe membrane lipid peroxidation occurred in the MPs groups. Metabolic pathways analysis showed that PS and A-PS perturbed the amino acid-related metabolic pathways. In particular, the amino acid biosynthesis and ATP-binding cassette (ABC) transporter pathways were significantly upregulated, thus promoting nitrogen storage and transmembrane transport in Dunaliella salina. Transmembrane transport requires a large amount of ATP; as a result, algal cell division is inhibited. In addition, A-PS stimulated more active glutathione metabolism than PS. These results enrich the understanding of the toxicity of PS MPs to microalgae at the metabolic level, and are helpful for further assessing the ecological impacts of MPs on microalgae.
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