Effects of continuous and pulse lead exposure on the swimming behavior of tadpoles revealed by brain-gut axis analysis.

Lead (Pb) is present in aquatic environments with a continuous or pulse form due to the regular or irregular discharge of wastewater. These two modes of exposure result in different toxicological effects on aquatic animals. To compare the effects of Pb exposure mode on the swimming behavior of amphibian larvae, this study proposed a combination method to examine the brain-gut axis (gut bacteria, histopathology, metabolomics, and ethology) in order to evaluate the ecotoxic differences in Pelophylax nigromaculatus tadpoles (Gs 21-28) when exposed to continuous (CE100) versus pulse exposure (PE100) of environmental concentrations of Pb (100 µg/L). The results showed that: 1) CE100 significantly decreased the movement distance and swimming activity of the tadpoles compared to PE100 and the control, while there were no significant differences between the control group and PE100. 2) At the phyla level, compared to PE100, CE100 treatment significantly decreased the abundance of Actinobacteria, Firmicutes, Proteobacteria, and Bacteroidetes and increased the abundance of Fusobacteria in the gut. At the genus level, compared to PE100, CE100 significantly increased the abundance of U114 and decreased the abundance of Anaerorhabdus, Exiguobacterium and Microbacterium. 3) Compared to PE100, CE100 changed the metabolites of the brain-gut axis pathway, such as quinolinic acid, L-valine, L-dopa, L-histidine, urocanic acid, L-threonine, γ-aminobutyric acid (GABA), L-glutamate (Glu), acetylcholine (Ach), L-tyrosine (Tyr), L-tryptophan (Trp), and levodopa (DOPA). 4) CE100 and PE100 played a repressive role in the histidine metabolism and tyrosine metabolism pathways and played a promoting role in the purine metabolism and pyrimidine metabolism pathways. This study provides a method for evaluating the toxic effects of heavy metal exposure via two different exposure modes (pulse versus continuous) which tadpoles may encounter in the natural environment from a combined study examining the brain-gut axis.

Influences of continuous and pulse atrazine exposure on intestinal flora and metabolites of Pelophylax nigromaculatus tadpoles.

Atrazine, a widely used herbicide, has adverse effects on the growth and metabolism of amphibians. Due to the cyclical application use of the pesticide atrazine in agricultural production, atrazine concentrations in water occur in the form of pulses. However, knowledge of the effects of atrazine pulse exposure on the gut microbiota and metabolism of amphibians is limited. In this study, Pelophylax nigromaculatus tadpoles (Gs 26) were exposed to continuous and pulse atrazine (100 µg/L) for 60 days. The results showed that continuous exposure and pulse exposure had different effects on the diversity of gut microbiota. At the phyla level, pulse exposure significantly increased the relative abundance of Actinobacteria, and decreased the relative abundance of Firmicutes compared to continuous exposure. At the genus level, continuous and pulse exposure to atrazine significantly altered the relative abundance of Acetobacterium, Microbacterium, Bacteroides, Eulopiscium and Leuconostoc. Compared to continuous exposure, pulse exposure significantly increased the relative abundance of Microbacterium, and significantly decreased the relative abundance of Acetobacterium and Eplopiscium. In terms of metabolism, pulse exposure significantly increased the relative abundance of creatine, guanine, and inosine and significantly decreased the relative abundance of 3-hydroxysebacic acid, ganoderic acid F, hypoxanthine, and withaperuvin H compared to continuous exposure. Continuous and pulse exposure to atrazine significantly altered the relative abundance of metabolites of the pymidine metabolism, purine metabolism, beta-alanine metabolism and other pathways in the gut of P. nigromaculatus tadpoles. In addition, changes in most metabolites had a significant correlation with changes in gut microorganisms. In conclusion, our study confirmed that pulse exposure to atrazine has a greater effect on the composition of the gut microflora and the metabolism of P. nigromaculatus tadpoles than continuous exposure.