Metabolomics profile of selenium-enriched Bacillus subtilis alleviating perfluorohexanoic acid-induced brain damage in Carassius auratus and its response to the intestinal microbial community

Perfluorohexanoic acid (PFHxA), a prevalent industrial pollutant, poses substantial threats to aquatic organisms. Selenium, a vital trace element in animal physiology, has demonstrated detoxifying ability. A recent research focus involves converting inorganic selenium into biological selenium through probiotics to enhance absorption. Our early-stage research found that selenium-rich Bacillus subtilis could ameliorate PFHxA-induced brain damage in Carassius auratus through the microbiota–gut–brain axis, although the metabolic products generated by endogenous substance reactions in Carassius auratus remained unknown. This study investigated how selenium-enriched Bacillus subtilis mitigated PFHxA-induced brain damage in Carassius auratus by examining growth indicators, measuring brain tissue cell apoptosis, and analyzing changes in Carassius auratus brain tissue metabolites using non-targeted metabolomics. In addition, a combined analysis of non-targeted metabolomics and intestinal microbiota was used to explore the alleviating effects of selenium-enriched Bacillus subtilis on PFHxA-induced brain damage in Carassius auratus. The results showed that the bacteria could alleviate PFHxA-inhibited growth and decrease brain tissue cell apoptosis. In the perfluorohexanoic acid group (PFHxA group), 490 differential metabolites were identified, with 257 being upregulated and 233 being downregulated. The levels of harmful metabolites, such as phthalates and ethoxyquin, were significantly increased. Conversely, in the selenium-enriched Bacillus subtilis + perfluorohexanoic acid group (Se + PFHxA group), 1604 differential metabolites were detected, with 409 being upregulated and 1195 being downregulated. The corresponding levels of harmful metabolites were significantly decreased, while the levels of protective metabolites such as L-glutathione were increased. There were significant alterations in the composition of the fish intestinal microbiota due to PFHxA exposure, with selenium-enriched Bacillus subtilis inducing significant changes in the microbial community. These changes were suggested to play a role in mitigating PFHxA-induced toxicity. Overall, our findings highlight the potential of selenium-enriched Bacillus subtilis as an effective supplement in aquaculture for the protection of Carassius auratus against environmental pollutants such as PFHxA, thereby providing valuable insights into complex interactions among diet, gut microbiota, and host metabolism in aquatic organisms exposed to environmental pollutants.