Studies On The Degradation Characteristics And Mechanism Of BDE-209 By Aerobic Bacteria Gordonia Sp.

Polybrominated diphenyl ethers are widely used worldwide for a typical class of brominated flame retardants,due to low price and excellent performance.As a Polybrominated diphenyl ethers with the largest number of bromine atoms,Decabromobiphenyl ether(BDE-209)has the characteristics of environmental persistence,bioaccumulation and low water solubility,is widely found in various environment media.Although BDE-209 is weak in toxicity,a series of migration and transformation may occur under the action of microorganisms in sediments and other environmental media,producing more toxic low-brominated diphenyl ethers.Therefore,it is necessary to master the microbial degradation characteristics and mechanism of BDE-209,providing basic data for evaluating its environmental and ecological effects.Based on collecting surface sediments and water samples from the Yangtze River estuary,this study analyzed the concentrations of the water quality parameters and BDE-209,as well as microbial community diversity.Furthermore,the bacteria degrading BDE-209 were selected from the sediments,systematically studying its characteristics and Mechanism of degradation.According to the geographic location,the sampling points were divided into intraoral(11 stations,salinity<1.00%)and external sampling stations(9 stations,salinity<2.50%).Based on the determination of water quality parameters in the overlying water sample of the sediment,including pH,dissolved oxygen,pressure,temperature,conductivity,nitrate,nitrite,phosphate,silicate,ammonia nitrogen and chlorophyll a,the distribution characteristic of water quality in the study area was analyzed.Using high-throughput sequencing technology to examine the distribution characteristics of microbial communities in the surface sediments of the Yangtze Estuary.By using RDA analysis,it was found that the microbial community composition of the surface sediments of the Yangtze Estuary has pH,salinity,dissolved oxygen,nitrate and nitrite significant correlation.The heavily polluted area with BDE-209 in the Yangtze River estuary was determined through investigation.With BDE-209 as the sole carbon source,the sediment in the corresponding station were used as the inoculum,a strain effectively degradating BDE-209(named BJ-1)was selected in the laboratory.morphological observation,physiological and biochemical index identification and 16S rDNA gene sequencing of the strain was performed.After identification,the strain was Gordonia sp.Through orthogonal experiments,the optimal growth conditions for this strain BJ-1 were determined to be pH=8,temperature 30?,salinity 2.94%and rotation speed 150 r·min-1.when the concentration of BDE-209 was 50 mg·L-1.the inoculation amount of strain BJ-1 was 10%,pH=8 and salinity was 3.20%,the degradation rate of BDE-209 could reach 78.77%on the 5th day of the reaction.Using gas chromatography-mass spectrometry to analyze the degradation products in the degradation system,BDE-207,BDE-199,BDE-184,BDE-154,BDE-101,BDE-52 and BDE-11 were main degradation products,inferring that BJ-1 mainly degraded BDE-209 by debromination.According to the 16S phylogenetic tree of BJ-1,the whole genome most similar to Gordonia sp.was selected to annotate Kyoto Encyclopedia of Genes and Genomes,meanwhile two metabolic pathway maps with complete annotations were obtained through matching the protein function annotation results with Kyoto Encyclopedia of Genes and Genomes pathway database,representing hexane and chlorobenzene metabolic pathways,as well as xylene metabolic pathways respectively.Meanwhile,according to the functional genes annotated by entire genome of the similar strain,Brenda,National Coalition Building Institute and SyntTax databases were used to performance functional enzyme homology analysis and gene cluster co-linear analysis.Whole genome analysis of similar strains indicated that strain BJ-1 may have genes encoding acetate dehalogenase,aryl alcohol dehydrogenase and catechol 2,3-dioxygenase,indicating that this strain has the foundation of biology degrading BDE-209.Furthermore,the upstream and downstream proteins of acetate dehalogenase,aryl alcohol dehydrogenase,and catechol 2,3-dioxygenase were selected for co-linear analysis through the SyntTax database,indicating that these functional enzymes had high colinearity with the strain of Gordonia sp.Combined with acetate dehalogenase,aryl alcohol dehydrogenase and catechol 2,3-dioxygenase of phylogenetic tree analysis,the results showed that it has certain genetic conservatism in Gordonia sp.,indicating that the isolated strain had the ability to degrade BDE-209.