| Polybromodiphenyl Ethers (PBDEs) are widely used in our life due to their high flame retardant effect, but they have caused adverse impact on human health and environment due to their high biotoxicant, persistence and bioaccumulation. Although the nitrate reduction coupling biodegradation of toxic organic contaminants occurs widespreadly in the ecological environment, yet there is no research report about degradation of PBDEs by nitrate-reducing bacteria. In this study, we use the four kinds of nitrate-reducing consortia which were enriched with Decabromodiphenyl ether (BDE-209) as target pollutants under nitrate reduction condition, to study the characteristics of BDE-209 degradation by nitrate-reducing bacteria. After optimizing the BDE-209 extraction and analysis conditions, the methods of PCR-DGGE, microbial isolation and identification, and the degradation kinetic analysis of targeted pollutants were used in this work.The main conclusions and understandings are as follows:(1) Against the uncertainty of slightly solubility and degradation characteristics of BDE-209, the impact of medium ingredients which is commonly used in microbial degradation study on the degradation of BDE-209 were analyzed, and the extraction conditions of BDE-209, microbial degradation systems and extraction methods are optimized and determined. It was found that sodium succinate could react chemically with BDE-209 and at least four new converted products generated. BDE-209 in water phase samples can be maximize recycled (97.82%) by repeatedly extracted with small amount of ethyl acetate and n-hexane. In addition, when dimethyl sulfoxide was used as the organic solvent for BDE-209, Shewanella decolorationis S12 could use BDE-209 as anaerobic respiration electron acceptor to increase biomass yield.(2) The BDE-209 degradation characteristics by the four consortia, which were obtained in the pre-enrichment cultures with or without the nitrate reducing bacterium Paracoccus sp. CY1 and sulfate reducing bacterium Citrobacter sp. SR3, are analyzed. The results showed that under anaerobic conditions, these four kinds of consortia have certain ability to reduce nitrate and degrade BDE-209. The highest denitrification rate (2.755 mg·L-1h-1) and degradation efficiency (57% in 75d) were obtained by the consortium CS, which was enriched under strains CY1 and SR3 coexistence condition, followed by consortium F without adding any exogenous bacteria (27.22% in 75d). The lowest degradation rates (-20% in 75d) were obtained by the other two consortia enriched only with strain CY3 or SR3. PCR-DGGE analysis showed that microbial community structures were significantly different among the four consortia, and Lysinibacillus sp., Enterococcus sp. and a lot of uncultured microorganisms were dominant in the communities. These results indicate that nitrate reducing consortia enriched with both nitrate-reducing bacteria and sulfate reducing bacteria addition could be better adapted to the contamination environment with nitrate and sulfate coexistance, and achieve higher BDE-209 degradation efficiencies.(3) The bacterial strain NA-7, having the ability to nitrate-reducing degrade BDE-209, was isolated and identified from CS consortium, which is more efficient on degradation of BDE-209. Based on the 16s rRNA gene sequences, strain NA-7 was belonged to Bacillus cereus. The BDE-209 degradation efficiency of strain NA-7 (～22.77% in 75d) was lower than CS consortium, and the proportions of main degradation products, Octa-BDEs and Nona-BDEs, were different with the consourtium with 4.73% and 0.32% for the consortium and 3.0% and 19% for the isolate, respectively. |
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