Polystyrene microplastics and cypermethrin exposure interfered the complexity of antibiotic resistance genes and induced metabolic dysfunction in the gut of adult zebrafish

Environmental pollutants such as microplastics (MPs) and pesticides are becoming prevalent in aquatic ecosystems, posing risks to wildlife and human health. This study investigated the toxicological effects of polystyrene microplastics (PS-MPs) and cypermethrin (CYP) on adult female zebrafish (Danio rerio), focusing on intestinal microenvironment. Adsorption kinetics experimental results showed that PS-MPs can adsorb a certain amount of CYP on its surface, thereby forming a new type of composite pollutant. After exposure to red fluorescent PS-MPs for 4 days, it was found that the PS-MPs could enter the zebrafish and accumulate in the intestines. Five-month-old female zebrafish were exposed to PS-MPs, CYP, and a mixture of both for 21 days. After exposure, feces were collected and analyzed using metagenomic sequencing to determine microbial composition and functional changes. Metagenomic sequencing of naturally excreted feces showed that co-exposure synergistically reduced α-diversity and shifted community structure, with marked losses of beneficial Fusobacteriota, Firmicutes and Cetobacterium somerae and enrichment of pathogenic Preplasmiviricota. Functional annotation indicated that PS-MPs alone up-regulated glycoside hydrolases and glycosyl-transferases, whereas CYP and the co-exposure group suppressed a great number of the top 50 carbohydrate-active enzymes and decreased secondary metabolic pathways linked to amino-acid, lipid and carbohydrate metabolism pathways. Antibiotic-resistance gene (ARGs) profiling identified 57 ARG types (such as sul1, adeF, lnuC and mphA) after co-exposure. Finally, key genes related to amino acid metabolism, carbohydrate metabolism, and lipid metabolism in intestinal tissue were significantly altered. Collectively, our data demonstrated that PS-MPs and CYP exposure amplified gut dysbiosis, metabolic dysfunction and ARG complexity in zebrafish. Overall, the study highlighted the potential risks of combined environmental pollutants on intestinal microbiota, with implications for ecosystem health.