Toxic effects of ammonia on intestinal health and microbiota in red-eared slider (Trachemys scripta elegans)

Ammonia is an important environmental pollutant and can induce serious damages to the organs of aquatic animals, especially the intestine which is mostly exposed to external environment. As important species of aquatic ecosystems, turtles may be potential risk targets of ammonia. However, it is not clear whether ammonia shows toxic effects on the intestines of turtles. Therefore, the worldwide species red-eared slider (Trachemys scripta elegans) was selected, to investigate the effects of ammonia on intestinal health and the composition of microbiota. Results showed that ammonia significantly changed the structure of intestines by decreasing the thickness of intestinal wall, shortening the length of intestinal villus, extending lamina proprias, and inducing inflammatory cells appearance when the turtles were exposed to ammonia (1.418 mg NH₃ L^-1) for 30 d. In addition, the downregulation of epithelial tight junction genes indicated that ammonia increased selective paracellular permeability. Simultaneously, the upregulation of cytokines suggested that ammonia induced intestinal immune and inflammatory responses. Furthermore, ammonia altered the dominant bacterial composition, and decreased the abundance of beneficial intestinal bacteria in the host. Our results demonstrated that ammonia impaired the intestinal health and changed the composition of residential microbiota in T. s. elegans. This study provides a new insight to evaluate the toxic effects of ammonia on aquatic turtles and helps to build a framework for the effective conservation of turtles.