Study On Dissolved Organic Matters Influence Mechanism Of Steroid Estrogen Degraded By Microorganism

Steroid estrogens (SEs) accumulated in aquatic may lead to some serious hazards to ecosystem and human endocrine system. SEs with low concentrations could adversely affect the reproductive health of aquatic organisms. Especially E2, only to lng·L-1 in the aquatic will cause the feminization of male fish. Thus, the fate and behaviors of E2 in the natural aquatic environment has been attracted extensive concern. Biodegradation was identified as one of the predominant removal approaches in water and sediment.First, Quinone-reducing bacteria was isolated from alkaline environment in ErHai Lake in Dali Yunnan. To isolate the quinone reducing bacteria, the incubation solution was diluted serially and plated on agar plates containing sodium formate and AQS. Selected well developed colonies were streaked three times onto new agar before further study. For identification of the quinone reducing bacteria, genomic DNA was extracted from the microbial cells grown on agar plates with standard extraction procedures. Phylogenetic analysis indicated that the closest relative of strain was Shewanella. strain with 99% 16r RNA gene sequence similarity. The strain Y2 represents the genus Shewanella within the family Shewanella in the phylum firmicutes. The reduction characteristics of AQS were studied by quinone-reducing bacteria, which showed the optimal pH value and optimal temperaturewith pH 7-8 and 25-30 ℃, respectively. And the process of AQS reduction was more suitable for dark anaerobic environment.Second, quinones or humics can be used as the only terminal electron acceptor coupling microbial growth to promote the biodegradation efficiency of E2. On the one hand, models of DOM were added to biodegradation experiment system, which induced the half-life value of E2 on decreasing. On the other hand, by adding LHA and LFA in MSM, the degradation efficiency of E2 will be improved 14.99% and 19.57%, respectively. Quinone groups in DOM can be used as the only terminal electron acceptor coupling microbial growth to promote the biodegradation efficiency of E2. Therefore, it is very important for quinone-reducing bacteria to wipe off steroid estrogen in alkaline environment.Last, whether the Fe(Ⅲ)/DOM can be used as electron shuttle system was explored. Fe(Ⅲ)/AQS as electron shuttle mediator was reasonable and the Fe(Ⅲ)/AQS facilitated microbial degradation of E2. We made the characterization for Fe and AQS, in order to prove the existence electron shuttle cycles of the Fe(Ⅲ)/AQS. Through AQS and Fe (Ⅱ) the change of the reaction, Fe(Ⅲ)/AQS used as an electron shuttle to mediate microbial degradation of E2. Fe(Ⅲ)/AQS as electron shuttle on E2 biodegradation efficiency was up to 2.36 times. In addition, the system does not directly effect on E2 in absence of quinone-reducing bacteria, despite the presence of dissolved organic matters or Fe (Ⅲ) co-exist Dissolve organic matters as electron shuttle material obviously promote microbial degradation of E2. The reason of it is that the scent properties of LFA is greater than LHA, which could lead to the electron transfer capability strong, leading to LFA mediated E2 biodegradation effect much stronger than the LHA.