Environmentally Relevant Sulfamethoxazole Induces Developmental Toxicity in Embryo-Larva of Marine Medaka ( Oryzias Melastigma )

Abstract

Abstract: Sulfamethoxazole (SMX), a commonly used sulfonamide antibiotic, poses a threat to aquatic life due to its widespread presence in the environment. This study aims to investigate the specific effects of SMX on the development of marine medaka (Oryzias melastigma) embryos and larvae. Marine medaka embryos were exposed to SMX at concentrations of 0 (SC group), 1 μg/L (L group), 60 μg/L (M group), and 1000 μg/L (H group). Embryonic development was observed under a stereomicroscope to note survival, hatching time, and heart rate. Lipid accumulation in the larval visceral mass was assessed using Oil Red O staining, while swimming patterns were simultaneously tracked for behavioral analysis. Gene expression related to embryonic/larval development, cardiovascular function, antioxidant activity, inflammation response, nervous system function, intestinal barrier integrity, detoxification processes, and lipid metabolism systems were analyzed using qPCR. Additionally, the microbial composition of the larvae was analyzed by performing 16S rDNA gene sequencing. The results indicated that SMX exposure significantly accelerated the heart rate of embryos and shortened the hatching time, while also causing anomalies such as reduced pigmentation, smaller eye size, spinal curvature, and yolk sac edema. SMX also led to a decrease in total length of larvae, increased lipid accumulation in the visceral mass, and increased swimming distance. At the molecular level, SMX exposure affected the transcript levels of genes involved in the cardiovascular system (ahrra, arnt2, atp2a1,and cacan1da), antioxidant and inflammatory systems (cat, cox-1, gpx, pparα, pparβ, and pparγ) , nervous system (gap43, gfap, α-tubulin) ,intestinal barrier function (claudin-1), detoxification enzymes (ugt2c1-like), and lipid metabolism (rxraa) in embryos to larval stage. Microbiome analysis showed that at the phylum level, SMX exposure increased the abundance of Proteobacteria and decreased the abundance of Bacteria. At the genus level, the abundance of Bacteria generally decreased, with a notable increase in the abundance of Vibrio in the H group. Alpha diversity analysis revealed a significant decrease in the Chao1 index in the L and H groups, indicating a reduction in microbial richness. Beta diversity analysis showed differences in the microbial communities of marine medaka larvae among different SMX exposure groups. This study elucidates the negative impacts of SMX on the development of marine medaka embryos and larvae and their microbial composition, providing a scientific basis for assessing the risks of SMX in marine ecosystems.

Keywords: Oryzias melastigma, Antibiotics, Sulfamethoxazole, Developmental Toxicity, Microbiome