Exposure to nitrate induced growth, intestinal histology and microbiota alterations of Bufo raddei Strauch tadpoles

Nitrate (NO3-) is one of the ubiquitous environmental chemicals which multiplies negative impacts on aquatic life such as amphibian larvae. However, the data involving the dynamics of amphibians in response to NO3-N are scarce. This study investigated the effects of NO3-N on locomotor ability, growth performance, oxidative stress parameters, intestinal histology, and intestinal microbiota of Bufo raddei Strauch tadpoles. The tadpoles were chronically exposed to different concentrations of NO3-N (10, 50, 100, and 200 mg/L) from Gosner stage 26 to 38. Our results revealed that NO3-N exposure caused significantly reduced body weight and length, impaired locomotor activity, and severe oxidative damage to liver tissue. Moreover, the high NO3-N (50, 100, and 200 mg/L) exposure caused irregular arrangement and indistinct cell borders of mucosal epithelial cells in the tadpoles intestine. The NO3-N exposure significantly changed the structure of the intestinal microbiota. The phylum Cyanobacteria occupy the main niche of intestinal microbes and have a certain negative correlation with the growth and motility of tadpoles. In addition, the functional prediction revealed that NO3-N exposure obviously downregulated the metabolism of enzyme families in tadpoles. Our comprehensive research shows the toxicity of NO3-N exposure in B. raddei Strauch, explores the potential links between development and intestinal microbiota of tadpole, and provides a new framework for the potential health risk of nitrate in amphibians.

Automated summary

This study investigated the effects of nitrate exposure on Bufo raddei Strauch tadpoles, including locomotor ability, growth performance, oxidative stress parameters, intestinal histology, and intestinal microbiota. The results showed that nitrate exposure significantly reduced body weight and length, impaired locomotor activity, caused oxidative damage to liver tissue, and changed the structure of intestinal microbiota. Overall, nitrate exposure was found to be toxic to B. raddei Strauch tadpoles.