Synergistic Effect of Glyphosate and Polyethylene Microplastics on Culturable Gut Microbiota Alterations in Zebrafish

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.