Nanoplastics enhance the intestinal damage and genotoxicity of sulfamethoxazole to medaka juveniles (Oryzias melastigma) in coastal environment

Antibiotics and nanoplastics are widely detected in the coastal ecosystem. However, the transcriptome mechanism elu-cidating the effect of antibiotics and nanoplastics co-exposure on the gene expression of aquatic organisms in coastal environment is still unclear. Here, single and joint effects of sulfamethoxazole (SMX) and polystyrene nanoplastics (PS-NPs) on the intestinal health and gene expression of medaka juveniles (Oryzias melastigma), which live in coastal en-vironment, were investigated. The SMX and PS-NPs co-exposure decreased intestinal microbiota diversity compared to the PS-NPs, and caused more adverse effect on the intestinal microbiota composition and intestinal damage com-pared to the SMX, indicating that PS-NPs might enhance the toxicity of SMX on the medaka intestine. The increased abundance of Proteobacteria in the intestine was observed in the co-exposure group, which might induce the intestinal epithelium damage. In addition, the differentially expressed genes (DEGs) were mainly involved in the drug metabolism-other enzymes, drug metabolism-cytochrome P450, metabolism of xenobiotics by cytochrome P450 path-ways in visceral tissue after the co-exposure. The expression of the host immune system genes (e.g., ifi30) could be as-sociated with the increased pathogens in intestinal microbiota. This study is useful for understanding the toxicity effect of antibiotics and NPs on aquatic organisms in coastal ecosystem.