ORIGINAL ABSTRACT

The coexistence of emerging pollutants, that is, microplastics (MPs) and pesticides poses significant threat to aquatic organisms. This study investigated the combined effects of polyethylene microplastics (PE-MPs) and glyphosate on the gut microbiome of zebrafish. Following a 21-day exposure, 16S rRNA sequencing revealed that co-exposure caused the most significant disruption, surpassing the individual effects of each stressor. Co-exposure resulted in the lowest alpha diversity and a distinct microbial community structure, characterized by the depletion of A. veronii and a marked enrichment of opportunistic pathogens like A. hydrophila. Clear separation of all exposed groups from controls, with the co-exposure group forming the most distinct cluster was observed in non-metric multi-dimensional scale analysis. Specifically, a higher number of ASVs were differentially abundant in the co-exposure group compared to the individual exposures. In the MPs group, Aeromonas species were markedly replaced by Enterobacter species. Glyphosate significantly enriched A. hydrophila species in the gut. Treatment-specific clustering, with Enterobacter species associated with MPs, and A. hydrophila with glyphosate and co-exposure groups were observed in Heatmap analysis. The findings indicate that microplastics not only act as direct stressors but also as glyphosate carriers, leading to amplified, non-additive shifts in the gut microbiome and posing a heightened ecological risk.