Catabolic Mechanism of 17β-Estradiol in <i>Rhodococcus erythropolis</i> KB1: Insights from Metabolomics, Genomics, and Transcriptomics

The release and prolonged retention of steroid hormones pose significant risks to both human health and the environment. Research on efficient-degrading bacteria at higher concentrations and their degradation pathways, genes, and enzymes is limited. In this study, <i>Rhodococcus erythropolis</i> KB1 efficiently degraded 96.75% of 50 mg/L 17β-estradiol (E2) within nine days. Including the 4,5- and 9,10-seco pathways, five putative degradation pathways were identified based on the analysis of metabolic intermediates and products using high-performance liquid chromatography-quadrupole-time-of-flight-mass spectrometry (HPLC-Q-TOF-MS). Under the proposed aerobic pathways, E2 undergoes hydroxylation or cleavage at ring A or B. The resultant products are subsequently converted into a common steroid metabolite, 3aα-H-4α(3'-propanoate)-7aβ-methylhexahydro-1,5-indanedione (HIP), via β-oxidation. HIP is further degraded through a central pathway and ultimately assimilated into the tricarboxylic acid (TCA) cycle. Whole-genome sequencing predicted a steroid degradation-related gene cluster on contig NZ_CP050127.1. Transcriptomic analysis demonstrated that the expression of the short-chain dehydrogenase (SDR) gene and three <i>cyp</i> genes in this gene cluster were significantly induced by E2. Additionally, the global response of E2 in strain KB1 was analyzed using transcriptome analysis. Various genes involved ATP-binding cassette (ABC) transport system, electron transfer and energetic metabolism, and stress response-were significantly increased in mRNA levels in response to strain KB1 that can use E2 as the single carbon source. These findings highlight strain KB1 as a promising candidate for E2 biodegradation, offer novel insights into the microbial mechanisms of E2 catabolism, and establish a theoretical basis for future applications.