Study On 17β-Estradiol Biodegradation Patterns And Characteriation By High-Efficiency Microbial Strains

Recently, environmental estrogen had received worldwide attention due to their negative effects on the endocrine systems of animal and humans. Several studies of estrogen pollution status and its degradation in environment had been conducted. In this study, with 17β-estradiol (E2) as a model hazardous pollutant, five E2-degrading bacteria were isolated from activated sludge, then the degradation patterns, the degradation characteristics and mechanism had been examined, which could provid some new strain materials and some basic parameters for the biodegradation in wastewater containing the estrogens.Several novel bacteria capable of degrading E2 were isolated from activated sludge collected from the wastewater treatment plant of an oral contraceptives producing factory in Xianju, Zhejiang. According to their morphology, physiochemical characteristics and 16S rDNA sequence analysis, these strains were identified as different bacterias in Bacillus sp. These strains were designated as E2-Y1,E2-Y2,E2-Y3,E2-Y4 and E2-Y5, respectively. These five strains were proposed as new species which can degrade E2 efficiently according to the relevant literatures. Based on the extent of E2 degradation as well as the production of E1 and its further transformation, two degradation patterns were identified. Pattern A: isolates in this group were able to degrade E2 but not E1. Strains E2-Y2,E2-Y3, E2-Y5 were capable of degrading 17β-estradiol, and these three strains decreased the estrogenic activity to 1/20 in 15 days, while E1 was increased and then accumulated during 8-day test period. Pattern B: isolates in this group were able to degrade both of E2 and E1. E2 was degraded completely by strains E2-Y1 and E2-Y4, and the estrogenic activity was decreased to 1/60 within 15 days. While after the initial accumulation of E1 during E2 degradation, 60% of E1 was degraded by these two isolates.Results of E2 degradation tests indicated that strain E2-Y4 could removed E2 completely after 4 days, the estrogenic activity was decreased to less than 1/60, and about 45% of E1 could be transformed in 9 days. The biodegradation efficiency was higher than that in other isolates, so the strain E2-Y4 was confirmed as the high-efficiency microbial strain which was capable of degrading E2. The optimal pH and temperature for E2 biodegradation in the shaking flasks were 7.5 and 30℃, respectively. The enhanced action of peptone and Lab-Lemco were quite obviously. Metal ions such as Ba²⁺,Zn ²⁺,Sn²⁺,Cd²⁺,Cr²⁺,Pb²⁺ inhibited the degradation, and the actions were ordinal increasing. The addition such as Ca²⁺,Fe²⁺,KNO3 and amylum had no obvious effect on the degradation of E2. Furthermore, this strain could degrade E2 completely within 7 days at initial concentration ranged from 0.5 to 50mg/L.It was also demonstrated that E2 biodegradation by E2-Y4 was catalyzed by catechol 1,2-dioxygenase. According to production analysis by GC/MS, it could be concluded that E2 was oxidized to E1 firstly, then 2-hydroxy-2,4-diene-1,6-dioic acid and butanedioic acid were produced, and finally degraded to CO2 and H2O by TCA-cycle.