| Polychlorinated biphenyls(PCBs)are typical persistent organic pollutants in the environment.The remediation of PCBs contaminated sediment remains a particularly difficult problem to solve.Hence,the cost-effective and environmentally sustainable microbial PCB degradation is of increasing interest.Under anaerobic conditions,microbial-catalyzed reductive dechlorination of PCBs is widespread,especially in natural sediments.However,PCB dechlorination activities are relatively site-specific,and influenced by many biogeochemical properties,which make it become extremely complex.Therefore,it is crucial to obtain an understanding of the characteristic as well as the mechanism of microbial PCB reductive dechlorination in a given environment,this will help in developing bioremediation schemes for PCB impacted sites.In the present research,dechlorination of 9 typical commercial PCB congeners including PCB5(23-CB),PCB12(34-CB),PCB64(236-4),PCB71(26-34-CB),PCB105(234-34-CB),PCB114(234-45-CB),PCB149(236-245-CB),PCB153(245-245-CB)and PCB170(2345-234-CB)was investigated in Taihu Lake sediment microcosms with the supplementation of 7.5mmol/L acetate,7.5 mmol/L fatty acid mixture(acetate: propionate: butyrate =1:1:1)and 3mmol/L nitrate,respectively.Furthermore,the shifts of microbial community and the abundance of dechlorinating-related microorganisms/dehalogenase in response to the added exogenous carbon sources and nitrate were exposed by using high-throughput sequencing technology and quantitative real-time PCR(q PCR)analysis,respectively.Moreover,the influence of PCB on biological denitrification in Taihu sediments was also investigated by analyzing the changes in nitrate nitrogen concentration,microbial community structure and denitrification functional genes over dechlorination process.The mian findings are as follows:(1)The presence of PCBs did not affect the biological denitrification of Taihu Lake sediments.(2)The supplementation of nitrate greatly inhibited the dechlorination of PCBs.Dehalococcoides and Dehalogenimonas could not become the dominant bacteria genus,and their relative abundances were only 0.06% and 0.6% respectively after 51 weeks of dechlorination.As a result,PCBs started to dechlorinate after a longer lag period(6～9 week);the total PCBs concentration reduction declined from 19.98±0.56% to 13.53±1.78%;the rare Ortho disappeared after adding nitrate;nitrate also extensively inhibited PF-Meta and SF-Para dechloriantion.(3)The results of q PCR analysis showed that the 16 S r RNA genes of Chloroflexi(putative dechlorinating bacterial),Dehalococcoides and the genes encoding reductive dehalogenases rdh 12,pcb A4,pcb A5 well indicated the dechloriantion in sediment microcosms without supplementary nitrate.However,in the nitrate-amended sediment microcosms,only Chloroflexi16 S r RNA and pcb A5 could indicate the acceleration of overall dechlorination and Meta dechlorination,respectively.(4)No matter whether short-chain fatty acids carbon source was added or not,the relative abundance of Dehalogenimonas was about 4 to 5 times that of Dehalococcoides after 24 weeks,which indicated that Dehalogenimonas were most likely responsible for the dechlorination of PCBs in the sediments The addition of short-chain fatty acids significantly increased the relative abundance of anaerobic fermentation bacteria Acidaminobacter,Youngiibacter,RBG-16-58-14,Leptolinea and ferric-reducing bacteria Geobacter and Geothermobacter.(5)The unassigned archaea OTU451 might be related to the dechlorination of PCBs.After15 weeks of incubation,its relative abundance increased significantly in the microcosms with or without added exogenous carbon source,from 5.71% to more than 17%. |
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