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

Abstract

Steroid hormones modulate development, reproduction and communication in eukaryotes. The widespread occurrence and persistence of steroid hormones have attracted public attention due to their endocrine-disrupting effects on both wildlife and human beings. Bacteria are responsible for mineralizing steroids from the biosphere. Aerobic degradation of steroid hormones relies on O 2 as a co-substrate of oxygenases to activate and to cleave the recalcitrant steroidal core ring. To date, two oxygen-dependent degradation pathwaysthe 9,10-seco pathway for androgens and the 4,5-seco pathways for oestrogens have been characterized. Under anaerobic conditions, denitrifying bacteria adopt the 2,3-seco pathway to degrade different steroid structures. Recent meta-omics revealed that microorganisms able to degrade steroids are highly diverse and ubiquitous in different ecosystems. This review also summarizes culture-independent approaches using the characteristic metabolites and catabolic genes to monitor steroid biodegradation in various ecosystems.

Genetic and metabolite biomarkers reveal actinobacteria-mediated estrogen biodegradation in urban estuarine sediment

“…Mineralization of natural estrogens is only accomplished by microorganisms (Thayanukul et al, 2010;Chen et al, 2017 andWang et al, 2020;Chiang et al, 2020). Complete estrogen mineralization by bacteria was first described by Coombe et al (1966) in actinobacterium Nocardia sp.…”

Channeling C1 Metabolism toward S -Adenosylmethionine-Dependent Conversion of Estrogens to Androgens in Estrogen-Degrading Bacteria

“…Due to these negative attributes, their abundance in the environment is of global importance. Biodegradation is considered the major process for the elimination of estrogens from the environment ( 7 – 9 ). Complete biodegradation of estrogens is only accomplished by microorganisms, and is mainly hampered by their low solubility in water (e.g., 1.5 mg liter −1 for estradiol) ( 10 ).…”

Anaerobic bacteria need their vitamin B 12 to digest estrogen

“…Because steroids are generally recalcitrant to degradation and can disrupt endocrine functions even at low concentrations in a variety of organisms including humans, the constant release of natural and synthetic steroids into the environment due to agriculture, industry, and sewage is of ever-increasing concern. Hence, bacteria capable of degrading steroids are valuable bioremediation agents (14,15). How bacteria deal with steroids is also important in the context of host-microbe metabolic interdependencies, including in pathogenesis (16).…”

“…Bacterial steroid degradation mechanisms, pathways, and intermediates are well characterized for androgens but less so for estrogens, and aerobic pathways are better charted than anaerobic ones, with most insights emerging from studies of some Actinobacteria and a few α-, β-, and γ-Proteobacteria (14,15). Thus, androgens are degraded aerobically via the 9,10-seco pathway (bond cleavage between ring B carbon atoms C9 and C10 to generate the corresponding secosteroid) or anaerobically in denitrifying bacteria via the 2,3-seco pathway (bond cleavage between ring A atoms C2 and C3) (14,15). Estrogens are more refractory to degradation due to their stable aromatic A-ring and are degraded in some aerobic bacteria by oxygenase-catalyzed cleavage of the bond between ring A atoms C4 and C5 (the 4,5-seco pathway) (14,15).…”

“…Thus, androgens are degraded aerobically via the 9,10-seco pathway (bond cleavage between ring B carbon atoms C9 and C10 to generate the corresponding secosteroid) or anaerobically in denitrifying bacteria via the 2,3-seco pathway (bond cleavage between ring A atoms C2 and C3) (14,15). Estrogens are more refractory to degradation due to their stable aromatic A-ring and are degraded in some aerobic bacteria by oxygenase-catalyzed cleavage of the bond between ring A atoms C4 and C5 (the 4,5-seco pathway) (14,15). Anaerobic estrogen degradation had been reported only in two bacterial species, and the genes and mechanisms involved have remained unknown.…”