Degradation characteristics and metabolic pathway of 17β-estradiol (E2) by Rhodococcus sp. DS201

In this study an E2-degrading bacterium was isolated from the activated sludge of a municipal treatment plant that treats the waste from a contraceptive medicine-processing factory in Beijing, China. Using the observed morphological and physiological features of the bacterium and 16S rRNA sequence analysis, this bacterial strain was identified as Rhodococcus sp. DS201. Using single-factor experiments and orthogonal tests, it was demonstrated that, when strain DS210 bacteria were inoculated into MM medium at an initial concentration of 1 mg/L with an initial pH of 7 and an inoculum amount of 1%, complete degradation of E2 by this strain was achieved within 3 days at 30oC. After strain DS201 had degraded the E2, several E2 metabolites were detected in the culture extracts using high-performance liquid chromatography (HPLC); they were then further identified using HPLC with tandem mass spectrometry (LC-MS/MS). Mass spectrum analysis of the E2 degradation identified the following products: pent-4-enoic acid; 2-ethyl-3-hydroxy-6-methylcyclohexane-1-carboxylic acid; 3-(7a-methyl-1,5-dioxooctahydro-1H-inden-4-yl) propanoic acid; and 5-hydroxy-4-(3-hydroxypropyl)-7a-methyloctahydro-1H-inden-1-one. These products have not previously been reported as parts of a mechanism for microbial E2 degradation and were suspected to be new metabolite products. Therefore, the E2 degradation pathway by strain DS201 is proposed herein.