Exposure to cadmium induced gut histopathological damages and microbiota alterations of Chinese toad (Bufo gargarizans) larvae.

Cadmium (Cd) is highly hazardous to both terrestrial and aquatic life and it also has multiple negative impacts on amphibian tadpoles and frogs. However, its effects on gut health of amphibian tadpoles are still poorly understood. We used Chinese toad (Bufo gargarizans) tadpoles to examine the effects of chronic cadmium exposure on gut histology and intestinal microbiota by using regular histology analysis and high-throughput sequencing techniques. Tadpoles were exposed to cadmium concentrations at 0, 5, 100 and 200 μg L-1 from Gosner stage 26 to 38. Our results showed 100 and 200 μg L-1 cadmium exposure caused severe gut histopathological alterations while 5 μg L-1 cadmium exposure induced subtle intestine damage. Moreover, species diversity, taxonomic composition and community structure of gut microbiota were influenced by cadmium exposure. Species diversity and richness decreased gradually with the increase of cadmium concentration. Microbial communities of tadpoles in 100 and 200 μg L-1 cadmium exposure groups were remarkably different from those in control group. Furthermore, the relative abundances of prevalent phyla such as Proteobacteria, Bacteroidetes and Firmicutes and dominant genera such as Klebsiella and Aeromonas were also affected by cadmium exposure. We concluded that cadmium could be harmful to tadpole health by inducing intestinal damages and gut microbiota changes.