Intestinal microbiota composition and physiological characteristics in bullfrog tadpoles with gas bubble accumulation

Intestinal gas bubble accumulation is a common phenomenon in bullfrog tadpoles that significantly increases mortality. The manipulation of gut microbiota composition holds potential for therapeutic applications in treating diseases. However, there remains an unexplored avenue in utilizing this manipulation to alleviate intestinal gas accumulation in bullfrog tadpoles. By using histological sectioning, physiological &amp; biochemical assays, and 16S rRNA high-throughput sequencing technology, we compared the gut microbiota composition and the physiological characteristics of host between normal tadpoles (ZC) and those with gas bubble accumulation (ZQ). The α-diversity index of gut microbiota did not significantly differ between the two groups (P > 0.05). ZC and ZQ shared 311 operational taxonomic units (OTUs), with 143 unique OTUs in ZC, and 278 OTUs in ZQ. The tadpole intestines’ major microbes included Fusobacteria, Proteobacteria, Firmicutes, Actinobacteria, Bacteroidetes, and Verrucomicrobiota. Compared with ZC, ZQ exhibited a significantly reduced abundance of Fusobacteria and an increased abundance of Proteobacteria (P < 0.05). At the genus level, ZQ significantly decreased the levels of Cetobacterium and norank_f__Barnesiellaceae (P < 0.05), whereas the levels of Citrobacter significantly increased (P < 0.05). The ZQ tadpoles exhibited damaged gill filaments, enlarged intercellular spaces in the intestinal epithelium, and a significant decrease in goblet cells. The ZQ tadpole liver cells displayed cell enlargement, nuclear displacement towards the periphery, and increased cytoplasmic vacuolisation. Additionally, compared with ZC, ZQ exhibited significantly elevated levels of total antioxidant capacity, malondialdehyde, acid phosphatase, and alkaline phosphatase activity in the liver. In conclusion, intestinal gas bubble accumulation in bullfrog tadpoles leads to changes in gut microbiota structure, with a decrease in beneficial bacteria and an increase in pathogenic bacteria. This disrupts intestinal homeostasis and affects liver health by exacerbating hepatocyte vacuolation and increasing oxidative stress. Our findings provide essential data for monitoring and treating this condition.