Biodegradation of Decabromodiphenyl Ether (BDE-209) by Crude Enzyme Extract from Pseudomonas aeruginosa

A critical review on BDE-209: Source, distribution, influencing factors, toxicity, and degradation

As the most widely used polybrominated diphenyl ether, BDE-209 is commonly used in polymer-based commercial and household products. Due to its unique physicochemical properties, BDE-209 is ubiquitous in a variety of environmental compartments and can be exposed to organisms in various ways and cause toxic effects. The present review outlines the current state of knowledge on the occurrence of BDE-209 in the environment, influencing factors, toxicity, and degradation. BDE-209 has been detected in various environmental matrices including air, soil, water, and sediment. Additionally, environmental factors such as organic matter, total suspended particulate, hydrodynamic, wind, and temperature affecting BDE-209 are specifically discussed. Toxicity studies suggest BDE-209 may cause systemic toxic effects on living organisms, reproductive toxicity, embryo-fetal toxicity, genetic toxicity, endocrine toxicity, neurotoxicity, immunotoxicity, and developmental toxicity, or even be carcinogenic. BDE-209 has toxic effects on organisms mainly through epigenetic regulation and induction of oxidative stress. Evidence regarding the degradation of BDE-209, including biodegradation, photodegradation, Fenton degradation, zero-valent iron degradation, chemical oxidative degradation, and microwave radiation degradation is summarized. This review may contribute to assessing the environmental risks of BDE-209 to help develop rational management plans.

Combining ozone and ultrasound technology to remove S2- in Bayer liquor

High content sulfur (S2-) in Bayer liquor can increase alkali consumption, accelerate equipment corrosion, especially seriously affect alumina production. The removal of S2- in Bayer liquor is studied using ultrasonic enhanced ozone method, which significantly improves the removal efficiency. Results indicate that the best removal efficiency of 93.83 % is obtained with reaction duration of 20 min, oxygen flow rate of 80 L/h, ultrasonic power of 60 W and reaction temperature of 60 °C. The comparative analysis shows that the removal efficiency of S2- is 25.34 % higher than that of ozone (O3) system after introducing ultrasound (US), indicating that US accelerates the mass transfer process of O3 and increases the hydroxyl radicals (OH) content. For further explanation of the mechanism of US/O3 system, EPR and XPS spectra are applied to analyze the content of free radical and the form of sulfur in Bayer liquor, indicating that the content of free radical in US/O3 system is more than US and O3 systems, and all sulfur is converted to SO42- after full oxidation.

The interaction mechanisms of co-existing polybrominated diphenyl ethers and engineered nanoparticles in environmental waters: A critical review

This review focuses on the occurrence and interactions of engineered nanoparticles (ENPs) and brominated flame retardants (BFRs) such as polybrominated diphenyl ethers (PBDEs) in water systems and the generation of highly complex compounds in the environment. The release of ENPs and BFRs (e.g. PBDEs) to aquatic environments during their usage and disposal are summarised together with their key interaction mechanisms. The major interaction mechanisms including electrostatic, van der Waals, hydrophobic, molecular bridging and steric, hydrogen and π-bonding, cation bridging and ligand exchange were identified. The presence of ENPs could influence the fate and behaviour of PBDEs through the interactions as well as induced reactions under certain conditions which increases the formation of complex compounds. The interaction leads to alteration of behaviour for PBDEs and their toxic effects to ecological receptors. The intermingled compound (ENPs-BFRs) would show different behaviour from the parental ENPs or BFRs, which are currently lack of investigation. This review provided insights on the interactions of ENPs and BFRs in artificial, environmental water systems and wastewater treatment plants (WWTPs), which are important for a comprehensive risk assessment.

Aerobic Degradation Characteristics and Mechanism of Decabromodiphenyl Ether (BDE-209) Using Complex Bacteria Communities

Complex bacteria communities that comprised Brevibacillus sp. (M1) and Achromobacter sp. (M2) with effective abilities of degrading decabromodiphenyl ether (BDE-209) were investigated for their degradation characteristics and mechanisms under aerobic conditions. The experimental results indicated that 88.4% of 10 mg L^-1 BDE-209 could be degraded after incubation for 120 h under the optimum conditions of pH 7.0, 30 °C and 15% of the inoculation volume, and the addition ratio of two bacterial suspensions was 1:1. Based on the identification of BDE-209 degradation products via liquid chromatography-mass spectrometry (LC-MS) analysis, the biodegradation pathway of BDE-209 was proposed. The debromination, hydroxylation, deprotonation, breakage of ether bonds and ring-opening processes were included in the degradation process. Furthermore, intracellular enzymes had the greatest contribution to BDE-209 biodegradation, and the inhibition of piperyl butoxide (PB) for BDE-209 degradation revealed that the cytochrome P450 (CYP) enzyme was likely the key enzyme during BDE-209 degradation by bacteria M (1+2). Our study provided alternative ideas for the microbial degradation of BDE-209 by aerobic complex bacteria communities in a water system.

Concentration profile, spatial distributions and temporal trends of polybrominated diphenyl ethers in sediments across China: Implications for risk assessment

Polybrominated diphenyl ethers (PBDEs) in sediments of China have been extensively investigated; however, most studies conducted to date have focused on specific locations, and the pollution and risk posed by these chemicals in sediments at the national scale remain unknown. Therefore, we analyzed the concentrations and risks of PBDEs in sediments in China and their spatiotemporal variations based on available literature. Overall, the sediments across China contain moderate to high levels of PBDEs, with BDE-209 being the dominant congener, followed by BDE-47 and BDE-99. The sediment concentrations of PBDEs were highest in southern China and lowest in northeastern China. Additionally, based on their PBDE concentrations, 18.4%, 30.0%, and 11.9% of sediment samples from rivers, lakes, and coastal waters, respectively, posed low to moderate eco-toxicological risks, but 6.90% of river sediments posed high risks. Between 2001 and 2017, the concentrations and risks of PBDEs in the sediments from rivers and coastal waters tended to decrease gradually. Additionally, there were low to moderate risks from PBDEs in lake sediments, and the risks in 2012-2017 were 3.30 times higher than those in 2006-2011. However, more studies about the spatial and temporal trends in PBDEs in sediment across China and their impacts on aquatic organisms are needed because there is still a general lack of relevant information.

Racial/ethnic and geographic differences in polybrominated diphenyl ether (PBDE) levels across maternal, placental, and fetal tissues during mid-gestation

Prenatal polybrominated diphenyl ether (PBDE) exposures are a public health concern due to their persistence and potential for reproductive and developmental harm. However, we have little information about the extent of fetal exposures during critical developmental periods and the variation in exposures for groups that may be more highly exposed, such as communities of color and lower socioeconomic status (SES). To characterize maternal-fetal PBDE exposures among potentially vulnerable groups, PBDE levels were examined in the largest sample of matched maternal serum, placenta, and fetal liver tissues during mid-gestation among a geographically, racially/ethnically, and socially diverse population of pregnant women from Northern California and the Central Valley (n = 180; 2014-16). Maternal-fetal PBDE levels were compared to population characteristics using censored Kendall's tau correlation and linear regression. PBDEs were commonly detected in all biomatrices. Before lipid adjustment, wet-weight levels of all four PBDE congeners were highest in the fetal liver (p < 0.001), whereas median PBDE levels were significantly higher in maternal serum than in the fetal liver or placenta after lipid-adjustment (p < 0.001). We also found evidence of racial/ethnic disparities in PBDE exposures (Non-Hispanic Black > Latina/Hispanic > Non-Hispanic White > Asian/Pacific Islander/Other; p < 0.01), with higher levels of BDE-100 and BDE-153 among non-Hispanic Black women compared to the referent group (Latina/Hispanic women). In addition, participants living in Fresno/South Central Valley had 34% (95% CI: - 2.4 to 84%, p = 0.07) higher wet-weight levels of BDE-47 than residents living in the San Francisco Bay Area. PBDEs are widely detected and differentially distributed in maternal-fetal compartments. Non-Hispanic Black pregnant women and women from Southern Central Valley geographical populations may be more highly exposed to PBDEs. Further research is needed to identify sources that may be contributing to differential exposures and associated health risks among these vulnerable populations.

Aerobic biodegradation pathways of pentabromobiphenyl ethers (BDE-99) and enhanced degradation in membrane bioreactor system

A bacterial strain capable of efficiently degrading pentabromobiphenyl ether (BDE-99) was isolated from activated sludge and named as NLPSJ-22. This strain was highly close to Pseudomonas asplenii with 100% similarity. The degradation products of BDE-99 were analyzed by gas chromatography mass spectrometry. The biochemical degradation pathways analysis indicated that BDE-99 gradually transformed to diphenyl ether by meta-, para- and ortho-debromination. It became phenol under the action of ring-opening cracking and finally entered the tricarboxylic acid cycle. The degradation of BDE-99 by strain NLPSJ-22 conformed to the first-order reaction kinetics. Rhamnolipid significantly improved the cell-surface hydrophobicity and the degradation of BDE-99. The highest degradation efficiency (96%) was achieved when diphenyl ether as co-metabolic substrate was added. In the bioaugmentation membrane bioreactor (MBR) system, BDE-99 was intensively degraded, and the reactor reached a steady state in about 35 days. The degradation rate of BDE-99 was over 80%, which was significantly higher than that of the control system. MiSeq sequencing results indicated that the genera of Rhodococcus, Bacillus, Pseudomonas, Burkholderia, and Sphingobium were the predominant bacterial communities responsible for BDE-99 biodegradation in the MBR. Pseudomonas increased significantly in the bioaugmented reactor with the relative abundance increasing from 5% to 24%.

Variation of Microbial Communities in Aquatic Sediments under Long-Term Exposure to Decabromodiphenyl Ether and UVA Irradiation

Abiotic components create different types of environmental stress on bacterial communities in aquatic ecosystems. In this study, the long-term exposure to various abiotic factors, namely a high-dose of the toxic chemical decabromodiphenyl ether (BDE-209), continuous UVA irradiation, and different types of sediment, were evaluated in order to assess their influence on the bacterial community. The dominant bacterial community in a single stress situation, i.e., exposure to BDE-209 include members of Comamonadaceae, members of Xanthomonadaceae, a Pseudomonas sp. and a Hydrogenophaga sp. Such bacteria are capable of biodegrading polybrominated diphenyl ethers (PBDEs). When multiple environmental stresses were present, Acidobacteria bacterium and a Terrimonas sp. were predominant, which equipped the population with multiple physiological characteristics that made it capable of both PBDE biodegradation and resistance to UVA irradiation. Methloversatilis sp. and Flavisolibacter sp. were identified as representative genera in this population that were radioresistant. In addition to the above, sediment heterogeneity is also able to alter bacterial community diversity. In total, seventeen species of bacteria were identified in the microcosms containing more clay particles and higher levels of soil organic matter (SOM). This means that these communities are more diverse than in microcosms that contained more sand particles and a lower SOM, which were found to have only twelve identifiable bacterial species. This is the first report to evaluate how changes in bacterial communities in aquatic sediment are affected by the presence of multiple variable environmental factors at the same time.

Response of Arthrobacter QD 15-4 to dimethyl phthalate by regulating energy metabolism and ABC transporters

Ubiquitous dimethyl phthalate (DMP) has severely threatened environmental safety and the health of organisms. Therefore, it is necessary to degrade DMP, removing it from the environment. Microbiological degradation is an efficient and safe method for degrading DMP. In this study, the response of Arthrobacter QD 15-4 to DMP was investigated. The results showed that the growth of Arthrobacter QD 15-4 was not impacted by DMP and Arthrobacter QD 15-4 could degrade DMP. RNA-Seq and RT-qPCR results showed that DMP treatment caused some changes in the expression of key genes in Arthrobacter QD 15-4. The transcriptional expressions of pstSCAB and phoU were downregulated by DMP. The transcriptional expressions of potACD, gluBC, oppAB, pdhAB, aceAF, gltA were upregulated by DMP. The genes are mainly involved in regulating energy metabolism and ATP-binding cassette (ABC) transporters. The increasing of pyruvic acid and citrate in Arthrobacter QD 15-4 further supported the energy metabolism was improved by DMP. It was clearly shown that Arthrobacter QD 15-4 made response to dimethyl phthalate by regulating energy metabolism and ABC transporters.

Response of Pseudomonas fluorescens to dimethyl phthalate

Dimethyl phthalate (DMP) is a ubiquitous pollutant that is very harmful to organisms due to its mutagenicity, teratogenicity and carcinogenicity. Pseudomonas fluorescens (P. fluorescens) is one of the most important bacteria in the environment. In this study, the response of P. fluorescens to DMP was investigated. It was found that DMP greatly inhibited the growth and glucose utilization of P. fluorescens when the concentration of DMP was ranged from 20 to 40 mg/l. The surface hydrophobicity and membrane permeability of P. fluorescens were also increased by DMP. DMP could lead to the deformations of cell membrane and the mis-opening of membrane channels. RNA-Seq and RT-qPCR results showed that the expression of some genes in P. fluorescens were altered, including the genes involved in energy metabolism, ATP-binding cassette (ABC) transporting and two-component systems. Additionally, the productions of lactic acid and pyruvic acid were reduced and the activity of hexokinase was inhibited in P. fluorescens by DMP. Clearly, the results suggested that DMP contamination could alter the biological function of P. fluorescens in the environment.

Cell changes and differential proteomic analysis during biodegradation of decabromodiphenyl ether (BDE-209) byPseudomonas aeruginosa

BDE-209 is a persistent organic pollutant. To promote microbial biodegradation of BDE-209 and gain further insight into its mechanism, cell changes and differential proteomic analysis ofP. aeruginosaduring biodegradation were studied.

Effects of rhamnolipids on the removal of 2,4,2,4-tetrabrominated biphenyl ether (BDE-47) by Phanerochaete chrysosporium analyzed with a combined approach of experiments and molecular docking

Effects of rhamnolipids on the removal of 2,4,2,4-tetrabrominated biphenyl ether (BDE-47) by Phanerochaete chrysosporium (P. chrysosporium) had been investigated, as well as the influence of carbon source (i.e. glucose). The results showed that the removal efficiency was over 90% in all treatments in 7 d. Rhamnolipids at low concentrations (0.05 and 0.1 CMC (critical micelle concentration)) could promote the removal of BDE-47, however, the inhibition effects occurred at high concentrations (0.5 and 1.0 CMC). The further study indicated that rhamnolipids at low concentrations not only promote the growth of mycelium, but also had obvious promotion on ligninolytic enzymes activity (i.e. manganese peroxidase (MnP), lignin peroxidase (LiP) and laccase (Lac)), especially for MnP and Lac. However, the opposite effect was generated at high rhamnolipids concentrations. Meanwhile, glucose played an active role for BDE-47 removal. For better understanding the degradation mechanism, the degradation product analysis and molecular docking had been introduced to this study. The degradation product analysis indicated that OH-PBDEs were the major degradation products and hydroxylation should be the important degradation pathway. The docking results showed that the ideal binding conformation occurred between ligninolytic enzymes and BDE-47, and hydrophobic interactions were the main interaction. Moreover, hydrogen bonds and hydrophobic interactions both existed in ligninolytic enzymes and rhamnolipids interaction. That might be the reason that rhamnolipids affected enzymes activity. These results indicated that P. chrysosporium might be a type of ideal microorganisms in the removal of BDE-47 pollution, and rhamnolipids could be a type of additives for better removal efficiency.

Biodegradation of decabromodiphenyl ether (BDE 209) by a newly isolated bacterium from an e-waste recycling area

Polybrominated diphenyl ethers (PBDEs) have become widespread environmental pollutants all over the world. A newly isolated bacterium from an e-waste recycling area, Stenotrophomonas sp. strain WZN-1, can degrade decabromodiphenyl ether (BDE 209) effectively under aerobic conditions. Orthogonal test results showed that the optimum conditions for BDE 209 biodegradation were pH 5, 25 °C, 0.5% salinity, 150 mL minimal salt medium volume. Under the optimized condition, strain WZN-1 could degrade 55.15% of 65 μg/L BDE 209 under aerobic condition within 30 day incubation. Moreover, BDE 209 degradation kinetics was fitted to a first-order kinetics model. The biodegradation mechanism of BDE 209 by strain WZN-1 were supposed to be three possible metabolic pathways: debromination, hydroxylation, and ring opening processes. Four BDE 209 degradation genes, including one hydrolase, one dioxygenase and two dehalogenases, were identified based on the complete genome sequencing of strain WZN-1. The real-time qPCR demonstrated that the expression level of four identified genes were significantly induced by BDE 209, and they played an important role in the degradation process. This study is the first to demonstrate that the newly isolated Stenotrophomonas strain has an efficient BDE 209 degradation ability and would provide new insights for the microbial degradation of PBDEs.

Effects of coexisting BDE-47 on the migration and biodegradation of BDE-99 in river-based aquifer media recharged with reclaimed water

Two prominent polybrominated diphenyl ether (PBDE) congeners have been included in the persistent organic pollutant list, 2,2',4,4',5-tetrabromodiphenyl ether (BDE-99) and 2,2,4,4'-tetrabromodiphenyl ether (BDE-47), which have been detected in treated municipal wastewater, river water, and sediments in China. A lab-scale column experiment was established to investigate the effects of the competitive sorption of BDE-47 on BDE-99 biodegradation and migration in two types of river-based aquifer soils during groundwater recharge with reclaimed water. Two types of recharge columns were used, filled with either silty clay (SC) or black carbon-amended silty clay (BCA). The decay rate constants of BDE-99 in the BCA and SC systems were 0.186 and 0.13 m^-1 in the single-solute system and 0.128 and 0.071 m^-1 in the binary-solute system, respectively, showing that the decay of BDE-99 was inhibited by the coexistence of BDE-47. This was particularly evident in the SC system because the higher hydrophobicity of BDE-99 determined the higher affinity and competition for sorption sites onto black carbon. The biodegradation of BDE-99 was suppressed by the coexistence of BDE-47, especially in the SC system. Lesser-brominated congeners (BDE-47 and BDE-28) and higher-brominated congeners (BDE-100, BDE-153, BDE-154, and BDE-183) were generated in the four recharge systems, albeit at different ratios. Bacterial biodiversity was influenced by the presence of BDE-47 in the SC system, while it had no significant effect on the BCA system, because the high sorption capacity of black carbon on the hydrophobic PBDEs effectively reduced their toxicity. The ranking order of the most abundant classes changed markedly due to the coexistence of BDE-47 in both the SC and BCA systems. The ranking order of the most abundant genera changed from Azospira, Methylotenera, Desulfovibrio, Methylibium, and Bradyrhizobium to Halomonas, Hyphomicrobium, Pseudomonas, Methylophaga, and Shewanella, which could be involved in PBDE degradation.

Vertical distribution of archaeal communities associated with anaerobic degradation of pentabromodiphenyl ether (BDE-99) in river-based groundwater recharge with reclaimed water

When groundwater is recharged with reclaimed water, the presence of trace amounts of biorefractory pentabromodiphenyl ether (PBDE, specifically BDE-99) might cause potential groundwater pollution. A laboratory-scale column was designed to investigate the distribution of the community of archaea in this scenario and the associated anaerobic degradation of BDE-99. The concentration of BDE-99 decreased significantly as soil depth increased, and fluorescence in situ hybridization (FISH) analysis suggested that archaea exerted significant effects on the biodegradation of PBDE. Through 454 pyrosequencing of 16s rRNA genes, we found that the distribution and structure of the archaeal community associated with anaerobic degradation of BDE-99 in the river-based aquifer media changed significantly between different soil depths. The primary debrominated metabolites varied with changes in the vertically distributed archaeal community. The archaea in the surface layer were dominated by Methanomethylovorans, and the middle layer was mainly composed of Nitrososphaera. Nitrosopumilus and Nitrososphaera were equally abundant in the bottom layer. In addition, Methanomethylovorans abundance depended on the depth of soil, and the relative abundance of Nitrosopumilus increased with increasing depth, which was associated with the oxidation-reduction potential and the content of intermediate metabolites. We propose that Nitrososphaera and Nitrosopumilus might be the key archaeal taxa mediating the biodegradation of BDE-99.

Biodegradation of cytotoxic 7-Ketocholesterol by Pseudomonas aeruginosa PseA

The present study aims to degrade 7-Ketocholesterol (7KC), a major oxysterol implicated in many age-related disorders, through microbial means and find candidate enzymes involved for further application in food systems and as a therapeutic. During initial screening of previously isolated bacteria from our laboratory, Pseudomonas aeruginosa PseA was found to be a potential degrader strain using 7KC as a sole carbon source. Under optimized conditions, it is able to degrade 88% of an initial concentration of 1000ppm (1g/l) 7KC. Preliminary in vitro studies with extra-cellular extract has shown degradation of the compound, thus reinforcing the occurrence of suitable enzymatic systems involved in the process. We have been able to identify cholesterol oxidase as one such potential enzyme. Some intermediate products of degradation have also been identified. This is the first detailed report of 7KC degradation by a P. aeruginosa strain.