Efficient removal of endocrine disrupting compounds 17 α-ethynyl estradiol and 17 β-estradiol by Enterobacter sp. strain BHUBP7 and elucidation of the degradation pathway by HRAMS analysis

Abstract

Owing to the increased population and their overuse, estrogens are being detected in the environment at alarming levels. They act as endocrine disrupting compounds (EDC's) posing adverse effects on animals and humans. In this study, a strain belonging to Enterobacter sp. strain BHUBP7 was recovered from a Sewage Treatment Plant (STP) situated in Varanasi city, U.P., India, and was capable of metabolizing both 17 α-Ethynylestradiol (EE2) and 17 β-Estradiol (E2) separately as a sole carbon source. The strain BHUBP7 exhibited high rates of E2 degradation as compared to EE2 degradation. The degradation of E2 (10 mg/L) was 94.3% after four days of incubation, whereas the degradation of EE2 (10 mg/L) under similar conditions was 98% after seven days of incubation. The kinetics of EE2 and E2 degradation fitted well with the first-order reaction rate. FTIR analysis revealed the involvement of functional groups like C = O, C-C, C-OH during the degradation process. The metabolites generated during degradation of EE2 and E2 were identified using HRAMS and a plausible pathway was elucidated. It was observed that metabolism of both E2 and EE2 proceeded with the formation of estrone, which was then hydroxylated to 4-hydroxy estrone, followed by ring opening at the C4-C5 position, and was further metabolized by the 4,5 seco pathway leading to the formation of 3-(7a-methyl-1,5-dioxooctahydro-1H-inden-4-yl) propanoic acid (HIP). It is the first report on the complete pathway of EE2 and E2 degradation in Enterobacter sp. strain BHUBP7. Moreover, the formation of Reactive Oxygen Species (ROS) during the degradation of EE2 and E2 was observed. It was concluded that both hormones elicited the generation of oxidative stress in the bacterium during the degradation process.

Keywords: 17 α-ethynylestradiol (EE2); 17 β-estradiol (E2); Endocrine disrupting compounds; Enterobacter sp..