Pathway of 17β-estradiol degradation by Nitrosomonas europaea and reduction in 17β-estradiol-derived estrogenic activity

Abstract

In recent years, natural and synthetic estrogens have been recognized as endocrine disruptors in aquatic organisms. Although natural and synthetic estrogens are known to be degraded by microbes, only limited information about their degradation pathways is available. Here, we studied the degradation pathways of a natural estrogen, 17b-estradiol, by the nitrifying microorganism Nitrosomonas europaea, and we determined whether the degradation products of 17b-estradiol had estrogenic activity. To identify the degradation products, we subjected the culture solution to solid-phase extraction, and the extract was analyzed by gas chromatography-mass spectrometry. The potential estrogenic activity of the degradation products was investigated by means of a yeast two-hybrid assay. 1,3,5(10),16-Estratetraen-3-ol (estratetraenol) was newly identified as a degradation intermediate produced by dehydration of 17b-estradiol. Estratetraenol was also degraded by N. europaea, and its degradation rate was faster than that of 17b-estradiol. The two-hybrid assay confirmed that estratetraenol acted as a ligand for the estrogen receptor; estratetraenol thus has potential estrogenic activity. N. europaea eliminated the estrogenic activity derived from 17b-estradiol. This paper is the first to report dehydration as a mechanism of microbial estrogen degradation.

Biochemical Mechanisms and Catabolic Enzymes Involved in Bacterial Estrogen Degradation Pathways

“…Prior to this study, no ring-cleaved metabolites derived from estrogens were identified. Although various estrogen biotransformation reactions have been proposed in estrogen-degrading bacteria (Coombe et al, 1966;Kurisu et al, 2010;Lee and Liu, 2002;Nakai et al, 2011;Yu et al, 2007), the structural elucidation of the estrogen metabolites was mostly based on MS. According to the chemical and biochemical analyses, we proposed an outline for the initial reactions of the estrogen catabolic pathway.…”

“…Estrogen-degrading bacteria have been isolated from various engineered and natural systems, including activated sludge, compost, soils, sandy aquifers, and the Baltic Sea; these isolates included microorganisms from the phyla Proteobacteria, Actinobacteria, Bacteroidetes, and Firmicutes (Yu et al, 2013 and references therein). Some biotransformation reactions have been proposed in the estrogen-degrading bacteria (Coombe et al, 1966;Kurisu et al, 2010;Lee and Liu, 2002;Nakai et al, 2011;Yu et al, 2007). Compared with the well-established aerobic biodegradation pathways of cholesterol (Bergstrand et al, 2016) and androgens (Horinouchi et al, 2012), current knowledge on estrogen degradation pathways is very limited.…”

Estrogen Degraders and Estrogen Degradation Pathway Identified in an Activated Sludge

“…1). In total, nine E2-derived degradation metabolites have been identified through mass spectrometry (MS) (24)(25)(26)(27)(28)(29). Six of the nine compounds are metabolites of estrogen degradation pathway I (i.e., the 4,5-seco pathway).…”

Mycoremediation of 17 β‐Estradiol Using Trichoderma citrinoviride Strain AJAC3 along with Enzyme Studies

“…The degradation steps follows release of HCOOH or CO 2 and hydroxylation of C-9 occurs producing keto group. Further, the B ring is reported to cleave followed by breakdown of D ring [1,32]. The GC MS analysis in this study shows that parent compound, E2 was degraded to glucose in the final stage.…”