Dynamic adaptations: Unraveling the skin microbiome of bullfrogs (Rana catesbeiana) under bacterial disease stress

Amphibians transition between aquatic and terrestrial environments throughout their lifecycle, a unique adaptation that fosters intimate interactions between their skin microbiome and the surrounding environment, thereby exhibiting distinctive and diverse microbial ecological characteristics. They are not only indicators of health but also harbingers of disease. This study focuses on bullfrogs (Rana catesbeiana) and comprehensively analyzes the dynamic changes in skin microbiomes under different disease conditions, revealing their crucial impact on host health. This study examines the skin microbiome of bullfrogs infected with three prevalent bacterial diseases (red-leg syndrome, edema syndrome, and meningitis-like infectious disease) in aquaculture settings, comparing them with microbiomes of healthy bullfrogs. Through 16S rDNA sequencing, a total of 1059 amplicon sequence variants (ASVs) were identified, encompassing 27 phyla, 57 classes, 133 orders, 223 families, and 398 genera. Among them, Bacteroidetes, Proteobacteria and Firmicutes are predominant bacterial phyla in the skin of healthy bullfrogs. At the genus level, compared to the healthy group (HS), bullfrogs with edema syndrome (ES) exhibited higher relative abundances of Acinetobacter, Arcobacter, and Aeromonas; bullfrogs with meningitis-like infectious disease (MID) showed higher relative abundances of Acinetobacter, Flavobacterium, Pedobacter, Arcobacter, and Comamonas; and bullfrogs with RLS showed higher relative abundances of Acinetobacter, Acinetobacter, Flavobacterium and Aeromonas. Simultaneously, significant functional changes were observed in the skin microbiota of MID. Compared to healthy bullfrogs, bullfrogs with ES exhibited marked alterations in pathways such as Carbohydrate metabolism, Xenobiotics biodegradation and metabolism, Metabolism of cofactors and vitamins, and Amino acid metabolism. Bullfrogs with MID showed pronounced disruptions in pathways related to energy metabolism, while those with RLS displayed notable dysregulation in Folding, sorting and degradation, Nervous system, and Translation pathways. These results indicate that changes in composition and function of the bullfrog skin microbiome are closely associated with their health status, with significant differences observed among microbiome characteristics under different disease conditions. These variations in the skin microbiome not only serve as important diagnostic markers for bacterial infections but also offer potential intervention strategies for the prevention and control of such diseases. A deeper understanding of these microbial changes' mechanisms could facilitate the development of novel disease management strategies, thereby enhancing the health management practices in bullfrog aquaculture.