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

Steroidal estrogens are often accumulated in urban estuarine sediments worldwide at microgram per gram levels. These aromatic steroids have been classified as endocrine disruptors with an EC50 at sub-nanomolar concentrations and classified as Group 1 carcinogens by the World Health Organization. Microbial degradation is a naturally occurring mechanism that mineralizes estrogens in the biosphere; however, the corresponding genes in estrogen-degrading actinobacteria remain unidentified. In this study, we identified a gene cluster encoding several putative estrogen-degrading genes in actinobacterium Rhodococcus sp. strain B50. Among them, the oecB and oecC genes involved in estrogenic A-ring cleavage were identified through gene-disruption experiments. We also detected the accumulation of two extracellular estrogenic metabolites, including pyridinestrone acid (PEA) and 3a-H-4(3-propanoate)-7a{beta}-methylhexahydro-1,5-indanedione (HIP), in the estrone-fed strain B50 cultures. Since actinobacterial oecC and proteobacterial oecC shared less than 40% sequence identity, oecC could serve as a specific biomarker to differentiate the contribution of actinobacteria and proteobacteria in environmental estrogen degradation. Therefore, oecC and the extracellular metabolites PEA and HIP were used as biomarkers to investigate estrogen biodegradation in an urban estuarine sediment. Interestingly, our data suggested that actinobacteria, rather than alpha-proteobacteria function in sewage treatment plants, are actively degrading estrogens in the urban estuarine sediment. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=139 SRC="FIGDIR/small/329094v1_ufig1.gif" ALT="Figure 1"> View larger version (93K): org.highwire.dtl.DTLVardef@17e1e23org.highwire.dtl.DTLVardef@ecc60borg.highwire.dtl.DTLVardef@be03d4org.highwire.dtl.DTLVardef@ed81d6_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightsO_LIIsolation of an estrogen-degrading actinobacterium Rhodococcus sp. strain B50 and establishment of a strain B50 genetic manipulation system. C_LIO_LIStrain B50 exhibits a two-fold estrogen degradation rate of that of estrogen-degrading alpha-proteobacteria under the same cultivation conditions. C_LIO_LIFunctional characterization of two oxygenase genes, oecB and oecC, involved in estrogenic A-ring cleavage in actinobacteria. C_LIO_LIIdentification of two extracellular estrogenic metabolites, PEA and HIP, in the estrone-fed strain B50 cultures. C_LIO_LIDetection of actinobacterial oecC sequences as well as PEA and HIP in the estrone-spiked urban estuarine sediments. C_LI