Gut Microbiota and Lipid Metabolism in Bullfrog Tadpoles: A Comparative Study Across Nutritional Stages

Our study investigated the growth-related metabolic changes and microbial community dynamics during the early feeding stage of bullfrog (<i>Lithobates catesbeiana</i>) tadpoles. In this research, we examined the changes in fat accumulation patterns, as well as the levels of biochemical and enzymatic indicators and genes mRNA expression related to lipid metabolism across the endogenous, mixed, and exogenous nutritional stages of bullfrog tadpoles from a single mating pair. Simultaneously, we characterized the community structures of intestines, excreta, and water bodies during these stages using 16S rRNA high-throughput sequencing technology. Our findings reveal that fat accumulation in tadpole tissues gradually increases with the onset of feeding. Levels of alanine aminotransferase, aspartate aminotransferase, triacylglycerol, total cholesterol, non-esterified fatty acid, high-density lipoprotein cholesterol and low-density lipoprotein cholesterol show a significant increase in exogenous nutritional stages. The mRNA levels of lipid synthesis-related genes and lipid degradation-related genes increased gradually with the changes of nutritional stage. Significant differences were observed in microbial community characteristics among intestines, excreta, and water bodies across nutritional stages. Specifically, gut microbiota exhibited a lower similarity to water body microbiota but a higher similarity to excreta microbiota. Notably, the phyla Firmicutes and Actinobacteriota, and the genus <i>Cetobacterium</i> within the gut microbiota, increased with nutritional changes. A Spearman correlation analysis highlighted a significant correlation between gut microbiota composition and lipid metabolism markers, particularly a strong positive association between <i>Cetobacterium</i> and lipid-related parameters. These insights provide a theoretical foundation for nutritional interventions aimed at enhancing tadpole growth and survival rates.