Atrazine exposure and recovery alter the intestinal structure, bacterial composition and intestinal metabolites of male Pelophylax nigromaculatus

Abstract

The pesticide atrazine poses a potential threat to the health of frogs living in farmland areas. The exposure concentration in traditional pesticide experiments is usually constant, while pesticide pollution in actual water may fluctuate due to periodic or seasonal application. We examined the effects of different concentrations of atrazine (50, 100 and 500 μg/L) over a 14-day exposure and a 7-day recovery on intestinal histology, bacterial composition and intestinal metabolites of male Pelophylax nigromaculatus. HE staining revealed that after a 14-day atrazine exposure, the 100 μg/L and 500 μg/L groups showed obvious cysts and significantly decreased intestinal crypt depth and villus height. After a 7-day recovery, the damaged intestine in the 100 μg/L group was partially recovered, while in the 500 μg/L exposure group there was no improvement. 16S rRNA gene analysis of intestinal bacteria showed that 500 μg/L atrazine exposure significantly caused a persistent decrease in bacterial α diversity. Compared to the control and other atrazine exposure groups, the 500 μg/L group showed significant changes in the relative abundance of predominant bacteria. In addition, most dominant bacteria in the 500 μg/L recovery group showed significant differences with the 50 μg/L and 100 μg/L recovery groups. Nontargeted metabolomics profiling based on UPLC/MS analysis showed that atrazine exposure and recovery induced changes in the intestinal metabolic profile. The changes in metabolites were mainly related to purine/pyrimidine metabolism, glycine, serine and threonine metabolism, and arginine and proline metabolism. In general, these pathways were closely related to energy metabolism and amino acid metabolism. These results suggest that the short-term exposure to 500 μg/L atrazine causes persistent harm to intestinal health. This study is an important step toward a better understanding of the toxic effects of atrazine exposure and recovery in frog intestines.