Steroid estrogens are natural hormonal compounds produced by various animals and humans. Estrone (E1), estradiol (E2), and estriol (E3) are the most commonly known estrogens that are released into the environment along with human and animal excreta, which end up polluting water bodies. While these estrogens are usually biotransformed into their respective by-products by various microbial strains, E2 could also be transformed into E1 by 17β-hydroxysteroid dehydrogenases (17β-HSDs) under reducing environmental conditions. However, due to limited further biotransformation of E1, it accumulates to higher levels in water bodies compared to other natural estrogens in the aquatic environment. Given that E1 is one of the potential endocrine-disrupting compounds (EDCs), with several adverse effects on aquatic animals and consequently on the seafood industry, it is vital to remove E1 from the environment via improved steroid bioremediation. In the present study, we successfully isolated a potential E1-degrading microbial strain (named as BH2-1) from soil sediments collected from the Bai Hai mangrove region of the South China Sea. The strain BH2-1 has excellent E1-degrading potential and could degrade 89.5% of E1 after 6 days of incubation in a MSM-E1 medium containing 1% NaCl at pH 6. Besides, after 3 h and 6 h of extraction, two non-accumulating intermediate compounds [3-hydroxyandrosta-5,7,9(11)-trien-17-one and androsta-1,4,6-triene-3,17-dione (ATD)], respectively, were successfully identified using GC-MS analysis. These non-accumulating intermediate compounds have not previously been reported during E1 biodegradation and might be new intermediate metabolites. The identification of these new compounds also gives more insight into the mechanism of E1 metabolism and helps to establish a clear E1 biodegradation pathway, which further enriches our knowledge on the overall microbial steroid degradation pathway. Furthermore, whole-genome sequence analysis of strain BH2-1 revealed the presence of 46 genes that belong to 6 major steroid-degrading gene classes.
Keywords: Biodegradation; Endocrine-disrupting compound; Estrone; Intermediate compounds; South China Sea; Steroid pollution.