Intestinal disruption and sex-dependent gut microbial responses following benzo[a]pyrene exposure in the male-pregnant seahorse Hippocampus erectus.

Benzo[a]pyrene (BaP) is a widespread marine pollutant with well-documented deleterious effects on aquatic organisms. However, its impacts on host intestinal responses and gut microbiota in species with reversed sex roles remain largely unclear. Using the male-pregnant seahorse Hippocampus erectus as a model, we investigated the effects of environmentally relevant BaP exposure on intestinal structure, transcriptomic profiles, and sex-dependent gut microbiota changes. BaP exposure induced concentration-dependent intestinal damage. Transcriptomic analyses revealed activation of xenobiotic metabolism and suppression of extracellular matrix-related pathways, indicating coupled detoxification responses and structural disruption of the intestinal barrier. Furthermore, BaP exposure reshaped the gut microbiota in a sex-dependent manner, characterized by enrichment of Ralstonia, Psychrobacter, and Acinetobacter in males and Akkermansia and Bacteroides in females. The sex-specific gut microbial responses may reflect underlying physiological differences between male and female seahorses. Despite the persistence of sexual dimorphism in gut microbial composition after BaP exposure, BaP reduced the extent of sex-specific divergence by decreasing the number of discriminative microbial biomarkers and attenuating functional differentiation between sexes. Overall, this study demonstrates that BaP disrupts intestinal homeostasis and reshapes gut microbiota in a sex-dependent manner, providing new insights into host-microbiota interactions under environmental stress in vertebrates with reversed sex roles.