Nitrite is a ubiquitous toxic compound in aquatic ecosystems and has negative effects on aquatic organisms. The intestine and the trillions of microbes that inhabit it, play an integral role in maintaining digestive and immune functions. However, the effects of nitrite on intestinal health and microflora have been poorly investigated. Therefore, the present study evaluated the response of intestinal histology, immunity, digestive enzyme activities and microbiota to nitrite exposure in Bufo gargarizans tadpoles. The results showed that nitrite caused damage to the intestine and impaired digestive performance. Significant changes in the transcriptional profiles of genes involved in oxidative stress (sod, gpx and hsp), inflammation, and immunity (socs3, il-27, il-1β and il-17d) were observed in the NO₂-N treatment groups. In addition, exposure to nitrite induced alterations of intestinal microbial diversity, structure and composition, suggesting that nitrite may lead to intestinal microbiota dysbiosis. It is noteworthy that probiotics (e.g., Bacteroidetes and Fusobacteria) were decreased after exposure to nitrite, whereas potentially opportunistic pathogens such as Proteobacteria and Enterobacteriaceae were elevated. Functional prediction and correlation analysis suggested that the above changes may interfere with metabolic function and trigger various diseases. Taken together, we concluded that nitrite exposure induced intestinal microbial dysbiosis, which may lead to immune dysfunction and metabolic disorder, and ultimately to histological damages in B. gargarizans. Further, this study will provide a scientific basis for further understanding the risk of nitrite pollution on the intestinal health of amphibians.

亚硝酸盐是水生生态系统中普遍存在的有毒化合物，对水生生物有负面影响。肠道和栖息在其中的数万亿微生物在维持消化和免疫功能方面发挥着不可或缺的作用。然而，亚硝酸盐对肠道健康和微生物群落的影响研究很少。因此，本研究评估了Bufo gargarizans蝌蚪肠道组织学、免疫、消化酶活性和微生物群对亚硝酸盐暴露的反应。结果表明，亚硝酸盐会损害肠道并损害消化功能。与氧化应激（ sod、gpx和hsp）、炎症和免疫有关的基因转录谱发生显着变化。_{在 NO 2} -N 治疗组中观察到socs3、il-27、il-1β和il-17d )。此外，暴露于亚硝酸盐会引起肠道微生物多样性、结构和组成的改变，这表明亚硝酸盐可能导致肠道微生物群失调。值得注意的是，暴露于亚硝酸盐后益生菌（如拟杆菌和梭杆菌）减少，而潜在的机会性病原体如变形杆菌和肠杆菌科被提升了。功能预测和相关性分析表明，上述变化可能会干扰代谢功能并引发各种疾病。总之，我们得出结论，亚硝酸盐暴露会导致肠道微生物菌群失调，这可能导致免疫功能障碍和代谢紊乱，并最终导致B. gargarizans的组织学损伤。此外，本研究将为进一步了解亚硝酸盐污染对两栖动物肠道健康的风险提供科学依据。