The toxic effects of chronic atrazine exposure on the intestinal microbiota, metabolism and transcriptome of Pelophylax nigromaculatus larvae

Atrazine, a widely used herbicide, is a potential threat to the intestines of animals due to its long-term persistence in water and accumulation in animal tissues, but the underlying mechanism is unclear. In this study, we evaluated the toxicity of atrazine (50, 100, and 500 µg/L) on the intestine of Pelophylax nigromaculatus larvae from Gosner stages 18–42 (about 90 days). We conducted a 16S rRNA gene amplification study, which showed that chronic exposure to atrazine changed the diversity and composition of intestinal microbiota of P. nigromaculatus larvae. Chronic exposure to atrazine (50, 100, and 500 µg/L) significantly decreased the relative abundance of Fusobacteria and U114, while 50 µg/L and 100 µg/L atrazine resulted in a significant increase of Clavibacter. The LC-MS/MS metabolomics indicated that there were 145 significantly changed metabolites. Furthermore, atrazine led to metabolic abnormalities related to purine metabolism and biosynthesis of amino acids in the intestine. The transcriptomic results showed that atrazine exposure caused 21,120 differentially expressed genes between the control and the atrazine exposure groups. Atrazine exposure primarily disturbed the pathways related to the cytokine-cytokine receptor interaction and cell adhesion molecules. Moreover, 500 µg/L atrazine caused a significant up-regulation in the gene expression of apolipoprotein (ApoA1, ApoB, and ApoA4), and fatty acid binding protein (FABP1), as well as a significant down-regulation in the gene expression of superoxide dismutase (SOD). Our work provides insight into the ecotoxicity mechanisms of atrazine in amphibians at the level of intestinal microbiota response, metabolome and transcriptome, and serves as a basis for future research on pesticide pollutants.