Effects of short-term continuous and pulse cadmium exposure on gut histology and microbiota of adult male frogs (Pelophylax nigromaculatus) during pre-hibernation

Cadmium (Cd) is an environmental endocrine-disrupting pollutant which mainly occurs in pulsed manner in natural waters, while traditional toxicology experiments have less examined the effects of pulsed exposure. Here, we studied the effects of short-term (7 days) continuous and pulse exposure to 100 μg/L Cd on gut morphology and microbiota of frogs ( Pelophylax nigromaculatus ) during pre-hibernation. Compared to continuous exposure, Cd pulse exposure significantly increased individual mortality and decreased the villi height and the ratio of villi height to crypt depth of the gut. Cd continuous and pulse exposure both changed the community structure and relative abundance of intestinal microbiota. Compared to continuous exposure, Cd pulse exposure significantly decreased the relative abundance of beneficial bacteria (e.g., Cetobacterium and Aeromonas genus), and significantly increased the relative abundance of harmful bacteria (e.g., Parabacteroides , Odoribacter , and Acinetobacter genus). This study shows that the gut histology and microbiota of amphibians during pre-hibernation are more susceptible to Cd pulse exposure than continuous exposure. • Cd exposure decreased the ratio of villi height to crypt depth of the gut. • Pulse Cd exposure increased the abundance of pathogenic bacteria. • Pulse Cd exposure decreased the abundance of beneficial bacteria.