Biochemical Mechanisms and Catabolic Enzymes Involved in Bacterial Estrogen Degradation Pathways

Abstract

Estrogens have been classified as group 1 carcinogens by the World Health Organization and represent a significant concern given that they are found in surface waters worldwide, and long-term exposure to estrogen-contaminated water can disrupt sexual development in animals. To date, the estrogen catabolic enzymes and genes remain unknown. Using a tiered functional genomics approach, we identified three estrogen catabolic gene clusters in Sphingomonas sp. strain KC8. We identified several estrone-derived compounds, including 4-hydroxyestrone, a meta-cleavage product, and pyridinestrone acid. The yeast-based estrogen assay suggested that pyridinestrone acid exhibits negligible estrogenic activity. We characterized 17β-estradiol dehydrogenase and 4-hydroxyestrone 4,5-dioxygenase, responsible for the 17-dehydrogenation and meta-cleavage of the estrogen A ring, respectively. The characteristic pyridinestrone acid was detected in estrone-spiked samples collected from two wastewater treatment plants and two suburban rivers in Taiwan. The results significantly expand our understanding of microbial degradation of aromatic steroids at molecular level.

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).…”

“…1. In our recent study (24), we used Sphingomonas sp. strain KC8, a wastewater isolate (25), as the model organism for aerobic estrogen degradation, and we identified 4-hydroxyestrone, a meta-cleavage product, and pyridinestrone acid (also known as pyridinestrone-3-carboxylic acid; see Fig.…”

“…Pyridinestrone acid was produced from the meta-cleavage product through an abiotic reaction with ammonium; therefore, pyridinestrone acid could be a dead-end product in the 4,5-seco pathway. We also sequenced the genome of strain KC8 and identified gene clusters likely to be involved in the degradation of A/B rings (gene clusters I and II) and C/D rings (gene cluster III) of E2 (24). Based on the results of the genomic and transcriptomic analyses as well as heterologous overexpression, we identified catabolic genes oecA and oecB, coding for 17␤-estradiol dehydrogenase and estrone 4-hydroxylase, respectively.…”

Microbial degradation of steroid sex hormones: implications for environmental and ecological studies

“…Except for 4‐norestrogen‐5(10)‐en‐3‐oyl‐CoA, no other CoA esters proposed in this aerobic pathway have been detected; however, at least five deconjugated (non‐CoA) metabolites corresponding to these hypothetical CoA esters have been detected in the bacterial cultures (Wu et al , ). The dead‐end‐products pyridinestrone acid and 4‐norestrogenic acid are less biodegradable and tend to accumulate in bacterial cultures (Wu et al , ) or environmental samples (Chen et al , , ); thus, these compounds may serve as biomarkers for investigating environmental aerobic oestrogen biodegradation.…”

“…Accordingly, it is speculated that these aerobes may adopt the 4,5‐ seco pathway for oestrogen degradation. Although the gene cluster for the oestrogen A/B‐rings degradation has been identified, only three catabolic genes – oecA , oecB and oecC – have been functionally characterized (Chen et al , ). The actual role of other genes, 2‐oxoacid oxidoreductase (OAOR), for example, remains to be validated.…”