Effects of different doses of microcystin-LR exposure on gut development and the microbiota of Xenopus laevis tadpoles

Abstract Background Although the acute toxicity of microcystin-LR has been widely confirmed, its effects on aquatic organisms at environmental concentrations have not been systematically studied. To reveal the effects of microcystin-LR on gut development and the microbiota of tadpoles, Xenopus laevis tadpoles were exposed to 0, 1, 5, 20, and 50 µg/L of microcystin-LR for 1, 7, 49, and 70 days (d) and the results were analyzed using histopathology, reverse transcription-quantitative polymerase chain reaction, and 16 S rRNA amplicon sequencing. Results Exposure to 5 µg/L microcystin-LR caused damage to the intestinal integrity and development of tadpoles, with the severity of damage increasing with higher concentrations. High concentrations of microcystin-LR (≥ 20 µg/L) significantly increased intestinal epithelial thickness over 49 d. Additionally, exposure to different concentrations of microcystin-LR had varying effects on the expression of TNF-α, IL-8, and TGF-β in the intestine, and microcystin-LR exposure at 50 µg/L continuously inhibited the expression of TGF-β. The relative abundances of Actinobacteria and Spirochaetes changed with sampling stages. In the samples taken at 49 d, Firmicutes and Tenericutes were significantly more abundant than in other samples, whereas Proteobacteria were significantly less abundant (p < 0.05). Microcystin-degrading Microbacterium, Bacillus, Pseudomonas, and Acinetobacter were the dominant bacteria in the gut microbiota. Conclusion These results suggested that exposure to different concentrations of microcystin-LR caused changes in the gut microbiota, potentially affecting the metabolism of microcystin-LR, and ultimately impacting the toxicity of microcystin-LR in X. laevis development.