Degradation Characteristics And Mechanism Of Aerobic Degrading Strains Degrading 2,2',4,4'-tetrabromodiphenyl Ether

Polybrominated diphenyl ethers(PBDEs),as a class of effective brominated flame retardants,are widely used in various industrial products such as electronic equipment,building and testile materials.PBDEs as one kind of persistent organic pollutants has contaminated the worldwide environment.Due to their stability,persistency,bioaccumulation in organisms,it's hard to be degraded by physical and chemical treatment methods.Recently,microbial degradation has been highly valued and widely used because of it's high degradation efficiency,minor pollution and low prices.In the present work,2,2',4,4'-tetrabrominated diphenyl ether(BDE-47)was chosen as the target compound to study the aerobic biodegradation process of PBDEs.Two aerobic BDE-47 degrading strains which could utilize BDE-47 as the sole carbon source were isolated from the PBDEs polluted paddy field soil at an electronic-waste(e-waste)recycling area in Guiyu,China.In addition,the effects of environmental conditions such as temperature,p H,substrate concentration on the biodegradation of BDE-47 were also investigated.Moreover,the BDE-47 metabolism products formed during the degradation process of both strains were identified and the biodegradation pathways of BDE-47 were proposed as well.At last,the biodegradation of other lower brominated diphenyl ethers and influence of additional carbon sources on the biodegradation of BDE-47 by these two strains and the influence of heavy metals by strain GYP4 were studied respectively.The main conclusions of this study are as follows:(1)Two highly effective aerobic strains for degrading BDE-47 were isolated successfully,named as GYP1 and GYP4.Based on the partial 16 S r DNA gene fragment(GYP1 about 1383 bp;GYP4 about 1471 bp)and sequence alignment,strain GYP1 and GYP4 were tentatively identified as Burkholderia cepacia,Achromobacter xylosoxidan,respectively.The nucleotide sequences of both strains were deposited under accession number(GYP1,KY697917;GYP4,KY697918)in the National Center for Biotechnology Information Genbank.The collection numbers of strain GYP1 and GYP4 are CCTCC No: M 2017103 and CCTCC No: M 2017104 in China Center for Type Culture Collection.(2)The degradation efficiencies of two strains and the effects of incubation conditions on BDE-47 degradation by strain GYP1 and GYP4 were investigated.Strain GYP1 and GYP4 could utilize BDE-47 as the sole carbon source and the degradation ratios of 1 mg L-1 BDE-47 by GYP1 and GYP4 were 82.4%,90.8%,respectively,after 4 days incubation.Strain GYP1 could maintain relatively high degrading efficiency for BDE-47 and the degradation ratios were all above 80% when the temperature was at 30 °C and p H value varied from 4.0~7.0;strain GYP4 could degrade BDE-47 efficiently and the degradation ratios were all above 80% when the temperature ranged from 25~35 °C and p H value varied from 3.0~7.0.(3)According to the UPLC-MS/MS analyses,during the BDE-47 degradation process,four OH-PBDEs(6-OH-BDE-47,5-OH-BDE-47,4'-OH-BDE-17,2'-OH-BDE-3)and one bromophenol(2,4-DBP)were detected in the incubation process of strain GYP1;three OH-PBDEs(6-OH-BDE-47,5-OH-BDE-47,4'-OH-BDE-17)and one bromophenol(2,4-DBP)were detected in the incubation process of strain GYP4.No lower brominated products and biphenyl ether were detected during the degradation of both strains.This suggested that the degradation pathways of BDE-47 by strain GYP1 and GYP4 were accompanied mainly by hydroxylation.(4)Strain GYP1 and GYP4 could also degrade BDE-28 and diphenyl ether.After four days incubation,the degradation ratios of 1 mg L-1 BDE-28 and 1 mg L-1 DE by strain GYP1 were 58.1%,82.6%,respectively.The degradation ratios of 1 mg L-1 BDE-28 and 1 mg L-1 DE by strain GYP4 were 58.0%,59.3%,respectively.Addition of sucrose,yeast extract and diphenyl ether inhibited the degradation efficiency of strain GYP1;addition of diphenyl ether inhibited the degradation efficiency of strain GYP4.At the presence of Cu2+ and Pb2+,bacteria GYP4 appeared varying degrees of shrinkage and sag,cell function declined,which decreased the degradation ratio of BDE-47.