Life-Cycle Diphenyl Phosphate (DPhP) Exposure Reveals Sex-Differential Functional Alterations in the Zebrafish Gut...

Fish gut microbiota is essential for maintaining host physiological health but is constantly threatened by environmental chemicals. Diphenyl phosphate (DPhP), a major degradation product of organophosphate flame retardants and an environmental pollutant widely detected in aquatic ecosystems, is a chemical of emerging concern; however, few studies have addressed its effects on the gut microbiota. In this study, zebrafish were exposed to environmentally relevant concentrations of DPhP (0.8, 3.9, or 35.6 μg/L) from the embryonic stage to adulthood over 120 days. Using V3-V4 region 16S rRNA gene sequencing and functional gene prediction, we systematically analyzed the sex-specific responses of the gut microbiota. The results showed that life-cycle DPhP exposure exerts markedly different effects on the gut microbiota of male and female zebrafish. In females, DPhP induced concentration-dependent, stepwise Tax4Fun2 predicted functional shifts suggestive of compensation: at the low concentration (0.8 μg/L), energy metabolism and cofactor/vitamin metabolism functions were predicted to be enhanced; at the medium concentration (3.9 μg/L), Fusobacteria (mainly Cetobacterium ceti) became dominant, accompanied by structural remodeling; at the high concentration (35.6 μg/L), genetic information processing and amino acid biosynthesis pathways were upregulated, suggesting active substance synthesis. In contrast, the gut microbiota of male zebrafish did not exhibit significant changes in diversity but showed widespread predicted functional impairment. Core energy metabolism and cofactor/vitamin metabolism functions were significantly suppressed, while taxa associated with pro-inflammatory phyla (Proteobacteria, Verrucomicrobia) expanded. Functional compensation in males was limited to xenobiotic degradation and fatty acid metabolism, suggesting a potential pathological shift. These findings suggest a sex-differential response of DPhP from the perspective of the gut microbiota, providing new evidence for the environmental risk assessment of organophosphorus flame retardants.