Mechanism and application potential of short-chain dehydrogenase in Rhodococcus sp. for the efficient degradation of 17α-ethynylestradiol

17α-Ethynylestradiol (EE2) is a ubiquitous synthetic estrogen of global concern. Due to its recalcitrance to biodegradation, EE2 is often insufficiently removed during wastewater treatment and consequently released with effluents, posing significant ecological risks and potential threats to human health. In this study, Rhodococcus equi DSSKP-R-001 ( R. equi -001) was identified as one of the most potent EE2-degrading bacterium, achieving complete degradation of EE2 at low concentrations. Transcriptomic analysis revealed substantial upregulation and high functional similarity of genes encoding short-chain dehydrogenase/reductase (SDR) during EE2 degradation. Among these candidates, sdr R was functionally validated as the most catalytically efficient, achieving 97.88 % EE2 removal. Molecular docking analyses demonstrated that the sdr R -mediated conversion of EE2 to estrone (E1) is facilitated by multiple key amino acid residues through substrate binding, hydrogen bonding, and hydrophobic interactions. Furthermore, the sdr R -harboring genetically engineered bacterium (GEB) exhibited superior biodegradation potential, achieving up to 96.48 % EE2 removal individually and enabling complete elimination when applied for bioaugmentation. Concurrently, bioaugmentation with GEBs reshaped the sludge microbial community by optimizing interspecies interactions and increasing the abundance of denitrifying and phosphorus-accumulating microorganisms, thereby improving overall pollutant removal performance. Overall, this study expands the microbial and enzymatic repertoire for EE2 degradation and demonstrate the potential of genetic engineering strategies for improving the removal of recalcitrant micropollutants in biological wastewater treatment.