Multi-Omics Reveals Gut Microbiota Shifts and Hepatic Metabolic-Immune Alterations in "Short-Leg" Malformed Frog (Pelophylax nigromaculatus).

Amphibian malformation syndromes significantly impact both conservation efforts and aquaculture, yet their underlying systemic pathophysiological mechanisms remain poorly characterized. This study comprehensively examines the multi-level pathological processes associated with the "short-leg" malformation syndrome in the black-spotted frog (Pelophylax nigromaculatus) using an integrated methodology, encompassing morphological, histopathological, gut microbiome, and hepatic transcriptomic analyses. Affected frogs demonstrated shortened limbs, impaired motor function, and a distinctive metabolic phenotype, including increased body weight despite a shorter body length, accumulation of visceral fat, and shortened intestines. Gut microbiota analysis identified significant compositional shifts, characterized by a decreased Firmicutes-to-Bacteroidota ratio, expansion of pro-inflammatory Proteobacteria, and reduction in beneficial Actinobacteriota, suggesting microbial niche restructuring that likely promotes metabolic and inflammatory disorders. Hepatic transcriptome profiling revealed 2617 differentially expressed genes, demonstrating a clear molecular dichotomy with concurrent up-regulation of immune-related pathways (e.g., neutrophil extracellular trap formation, complement cascades, and inflammatory signaling) and broad suppression of metabolic pathways (e.g., lipid oxidation, nutrient absorption, and PPAR and renin-angiotensin systems). This integrated analysis illustrates that the malformation syndrome represents a systemic pathophysiological state involving dysfunction of the gut-liver axis, characterized by the coexistence of gut microbiota alterations, hepatic metabolic suppression, and immune activation. These findings provide a framework for understanding amphibian malformations and suggest potential strategies to improve health outcomes in aquaculture.