Metabolomic and microbial responses of multilevel aquatic organisms to antibiotics in freshwater microcosm: The uniformity and specificity

The widespread presence of antibiotics in aquatic environments raises concerns about their ecological impacts. However, the molecular-level effects of antibiotics and the underlying mechanisms, particularly the responses across aquatic species, remain unclear. We established a freshwater microcosm including duckweeds ( Salvinia natans ), snails ( Cipangopaludina cathayensis ), and fish ( Danio rerio ) to investigate their uniform and specific responses to antibiotics (sulfamethoxazole, ciprofloxacin, oxytetracycline, and azithromycin), each at 1, 10, and 100 μg/L for 45 days. Antibiotic exposure diminished chlorophyll content in duckweeds, increased soluble sugar levels, elevated triglyceride levels in snails, and raised total bile acid concentrations in fish. Metabolomic analysis revealed that both duckweeds and fish tended to store energy to defend against antibiotic-induced stress, but through different pathways. Duckweeds accumulated sugar metabolites and downregulated antioxidants, while fish consumed primary sugars and converted them into lipid metabolites. Microbiome analysis indicated a self-coordination of gut bacteria in both snails and fish exposed to 1 and 10 μg/L of antibiotics, while dysbiosis occurred in snails at 100 μg/L, marked by increased pernicious bacteria abundance. In contrast, the abundance of probiotic bacteria increased in the fish gut due to microbial resistance to antibiotics, which played a crucial role in bile acid metabolism and positively influenced hepatic lipid metabolism via the gut-liver axis. This study uncovered the uniform and specific defense and dysregulation behaviors of multilevel aquatic organisms in response to antibiotic exposure, providing valuable insights into the selection of molecular-level endpoints for water quality benchmark development to safeguard aquatic life from antibiotic pollution.