Contributions of enzymes and gut microbes to biotransformation of perfluorooctane sulfonamide in earthworms (Eisenia fetida)

Perfluorooctane sulfonamide (FOSA) is known as a key intermediate of perfluorooctane sulfonic acid (PFOS) precursors, which can be frequently detected in the environment and biota. FOSA could be bioaccumulated in earthworms from soil, but the contributions of enzymes and gut microbes involved in the biotransformation of FOSA in earthworms have not been identified. Therefore, the effects of enzyme inhibitors and intestinal microflora on biotransformation of FOSA in earthworms were investigated in the present study. FOSA was biotransformed to form PFOS by earthworms obtained from in vivo and in vitro tests. The addition of FOSA had significantly positive effects on cytolchrome P450 (CYP450) and glutathione- s -transferase (GST) activities, suggesting CYP450 and GST are likely involved in the enzymatic transformation. In addition, both 1-Aminobenzotriazole (ABT) and ezatiostat hydrochloride (TLK199), which were selected to inhibit the CYP and GST enzymes, respectively, demonstrated inhibition effects on biotransformation of FOSA in earthworms with a dose-dependent relationship. However, the concentrations of FOSA weren't changed by the bacteria isolated from worm gut, suggesting that gut bacteria did not contribute to FOSA biotransformation in earthworms. The results of this study confirm that the transformation of FOSA in earthworms is mediated mainly by enzymes rather than by gut microbes.