Loss of the ssrA genome island led to partial debromination in the PBDE respiring Dehalococcoides mccartyi strain GY50

Polybrominated diphenyl ethers (PBDEs), chemicals commonly used as flame‐retardants in consumer products, are emerging persistent organic pollutants that are ubiquitous in the environment. In this study, we report a PBDE‐respiring isolate – Dehalococcoides mccartyi strain GY50, which debrominates the most toxic tetra‐ and penta‐BDE congeners (～1.4 µM) to diphenyl ether within 12 days with hydrogen as the electron donor. The complete genome sequence revealed 26 reductive dehalogenase homologous genes (rdhAs), among which three genes (pbrA1, pbrA2 and pbrA3) were highly expressed during PBDE debromination. After 10 transfers of GY50 with trichloroethene or 2,4,6‐trichlorophenol as the electron acceptor instead of PBDEs, the ssrA‐specific genome island (ssrA‐GI) containing pbrA1 and pbrA2 was deleted from the genome of strain GY50, leading to two variants (strain GY52 with trichloroethene, strain GY55 with 2,4,6‐trichlorophenol) with identically impaired debromination capabilities (debromination of penta‐/tetra‐BDEs ceased at di‐BDE 15). Through analysis of Illumina paired‐end sequencing data, we identified read pairs that probably came from variants that contain ssrA‐GI deletions, indicating their possible presence in the original strain GY50 culture. The two variant strains provide real‐time examples on rapid evolution of organohalide‐respiring organisms. As PBDE‐respiring organisms, GY50‐like strains may serve as key players in detoxifying PBDEs in contaminated environments.     

Effect of Fe-Pd bimetallic nanoparticles on Sphingomonas sp. PH-07 and a nano-bio hybrid process for triclosan degradation

In this study, we have evaluated the effect of palladium-iron bimetallic nanoparticles (nFe-Pd) on diphenyl ether (DE) degrading bacterial strain Sphingomonas sp. PH-07 as well as a sequential nano-bio hybrid process with nFe-Pd as catalytic reductant and PH-07 as biocatalyst for degradation of triclosan. Strain PH-07 grew well in the presence of nFe-Pd up to 0.1 g/L in minimal salts medium with DE as carbon source. In aqueous system, TCS (17.3 μM) was completely dechlorinated within 2 h by nFe-Pd (0.1 g/L) with concomitant release of 2-phenoxyphenol (16.8 μM) and chloride ions (46 μM). All possible dichloro- and monochloro-2-phenoxyphenol intermediates were identified by HPLC and GC-MS analyses, and the dechlorination pathway was proposed. Addition of PH-07 cells into the reactor effectively degraded the 2-phenoxyphenol. Our results reveal that strain PH-07 survives well in the presence of nFe-Pd and nFe-Pd/PH-07 hybrid treatment could be a potential strategy for degradation of TCS.     

Biodegradation of 1,4-dioxane and transformation of related cyclic compounds by a newly isolated Mycobacterium sp. PH-06

A new bacterial strain PH-06 was isolated using enrichment culture technique from river sediment contaminated with 1,4-dioxane, and identified as belonging to the genus Mycobacterium based on 16S rRNA sequencing (Accession No. EU239889). The isolated strain effectively utilized 1,4-dioxane as a sole carbon and energy source and was able to degrade 900 mg/l 1,4-dioxane in minimal salts medium within 15 days. The key degradation products identified were 1,4-dioxane-2-ol and ethylene glycol, produced by monooxygenation. Degradation of 1,4-dioxane and concomitant formation of metabolites were demonstrated by GC/MS analysis using deuterium labeled 1,4-dioxane (1,4-dioxane-d8). In addition to 1,4-dioxane, this bacterium could also transform structural analogues such as 1,3-dioxane, cyclohexane and tetrahydrofuran when pre-grown with 1,4-dioxane as the sole growth substrate. Our results suggest that PH-06 can maintain sustained growth on 1,4-dioxane without any other carbon sources.     

Isolation of Acetobacterium sp. Strain AG,Which Reductively Debrominates Octa- and Pentabrominated Diphenyl Ether Technical Mixtures

Polybrominated diphenyl ethers (PBDEs) are a class of environmental pollutants that have been classified as persistent organic pollutants since 2009. In this study, a sediment-free enrichment culture (culture G) was found to reductively debrominate octa- and penta-BDE technical mixtures to less-brominated congeners (tetra-, tri-, and di-BDEs) via a para-dominant debromination pattern for the former and a strict para debromination pattern for the latter. Culture G could debrominate 96% of 280 nM PBDEs in an octa-BDE mixture to primarily tetra-BDEs in 21 weeks. Continuous transferring of culture G with octa-/penta-BDEs dissolved in n-nonane or trichloroethene (TCE) yielded two strains (Acetobacterium sp. strain AG and Dehalococcoides sp. strain DG) that retained debromination capabilities. In the presence of lactate but without TCE, strain AG could cometabolically debrominate 75% of 275 nM PBDEs in a penta-BDE mixture in 33 days. Strain AG shows 99% identity to its closest relative, Acetobacterium malicum. In contrast to strain AG, strain DG debrominated PBDEs only in the presence of TCE. In addition, 18 out of 19 unknown PBDE debromination products were successfully identified from octa- and penta-BDE mixtures and revealed, for the first time, a comprehensive microbial PBDE debromination pathway. As an acetogenic autotroph that rapidly debrominates octa- and penta-BDE technical mixtures, Acetobacterium sp. strain AG adds to the still-limited understanding of PBDE debromination by microorganisms.     

Triclosan susceptibility and co-metabolism--a comparison for three aerobic pollutant-degrading bacteria

The antimicrobial agent triclosan is an emerging and persistent environmental pollutant. This study evaluated the susceptibility and biodegradation potential of triclosan by three bacterial strains (Sphingomonas wittichii RW1, Burkholderia xenovorans LB400 and Sphingomonas sp. PH-07) that are able to degrade aromatic pollutants (dibenzofuran, biphenyl and diphenyl ether, respectively) with structural similarities to triclosan. These strains showed less susceptibility to triclosan when grown in complex and mineral salts media. Biodegradation experiments revealed that only strain PH-07 was able to catabolize triclosan to intermediates that included hydroxylated compounds (monohydroxy-triclosan, and dihydroxy-triclosan) and the ether bond cleavage products (4-chlorophenol and 2,4-dichlorophenol), indicating that the initial dihydroxylation occurred on both aromatic rings of triclosan. Additional growth inhibition tests demonstrated that the main intermediate, 2,4-dichlorophenol, was less toxic to strain PH-07 than was triclosan. Our results indicate that ether bond cleavage might be the primary mechanism of avoiding triclosan toxicity by this strain.     

The microbial degradation of halogenated diaryl ethers

The structurally related polyhalogenated diaryl ethers such as diphenyl ethers (DEs), dibenzofurans (DFs), and dibenzo-p-dioxins (DDs) are regarded, due to their physicochemical and toxicological properties, as a class of compounds giving reason for serious environmental concern. While the nonhalogenated basic structures are biodegradable under aerobic conditions, there is the need for rather specialized strains to mineralize the halogenated derivatives. Certain halogenated metabolites might cause serious problems such as having inhibitory effects upon the degradation. Anaerobic methanogenic consortia do have the ability to almost completely dehalogenate even polyhalogenated congeners. It has been shown that certain fungi are capable of transforming chlorinated DFs and DDs by the activity of nonspecific enzymes such as lignin-peroxidases.     

Identification and biodegradation efficiency of a newly isolated 2,2′,4,4′-tetrabromodiphenyl ether (BDE-47) aerobic degrading bacterial strain

Polybrominated diphenyl ethers (PBDEs) are bioaccumulative, toxic and persistent, globally distributed organic chemicals in environment. However, very little is known for their aerobic biodegradation. In this research, 2,2′,4,4′-tetrabromodiphenyl ether (BDE-47) was selected as a model congener of PBDEs to study its aerobic biodegradation. A new BDE-47 degrading strain BFR01 identified as Pseudomonas stutzeri was isolated from polluted soil in a former brominated flame retardant production corporation. Stain BFR01 could utilize BDE-47 as a sole source of carbon and energy, and transformed 97.94% of BDE-47 in two weeks; the biodegradation of BDE-47 fitted well with the first-order kinetics, with the first-order kinetics constant of 0.32 d⁻¹. The biodegradation efficiency of stain BFR01 was higher than other reported PBDEs aerobic degrading bacteria. The biodegradation efficiency achieved maximum at pH 7.0 and 40 °C. The presence of additional carbon sources could enhance the biodegradation efficiency of BDE-47 by 1–6%. Furthermore, no lower brominated diphenyl ethers or biphenyl were detected, suggesting that the pathway of BDE-47 biodegradation by strain BFR01 might not be debromination with lower brominated diphenyl ethers as products. This is the first report of aerobic degradation of BDE-47 by P. stutzeri.     

Biphenyl and ethylbenzene dioxygenases of Rhodococcus jostii RHA1 transform PBDEs

Polybrominated diphenyl ethers (PBDEs) are a class of flame retardants that have been widely used in consumer products, but that are problematic because of their environmental persistence and endocrine‐disrupting properties. To date, very little is known about PBDE degradation by aerobic microorganisms and the enzymes involved in PBDE transformation. Resting cells of the polychlorinated biphenyl‐degrading actinomycete, Rhodococcus jostii RHA1, depleted nine mono‐ through penta‐BDEs in separate assays. Extensive depletion of PBDEs occurred with cells grown on biphenyl, ethylbenzene, propane, or styrene, whereas very limited depletion occurred with cells grown on pyruvate or benzoate. In RHA1, expression of bphAa encoding biphenyl dioxygenase (BPDO) and etbAa1 and etbAc encoding ethylbenzene dioxygenase (EBDO) was induced 30‐ to 3,000‐fold during growth on the substrates that supported PBDE depletion. The BPDO and EBDO enzymes had gene expression profiles that matched the PBDE‐depletion profiles exhibited by RHA1 grown on different substrates. Using the non‐PBDE‐degrading bacterium Rhodococcus erythropolis as a host, two recombinant strains were developed by inserting the eth and bph genes of RHA1, respectively. The resultant EBDO extensively depleted mono‐ through penta‐BDEs, while the BPDO depleted only mono‐, di‐, and one tetra‐BDE. A dihydroxylated‐BDE was detected as the primary metabolite of 4‐bromodiphenyl ether in both recombinant strains. These results indicate that although both dioxygenases are capable of transforming PBDEs, EBDO more potently transforms the highly brominated congeners. The availability of substrates or inducing compounds can markedly affect total PBDE removal as well as patterns of removal of individual congeners. Biotechnol. Bioeng. 2011;108: 313–321. © 2010 Wiley Periodicals, Inc.     

Biodegradation of Dibenzo-p-dioxin, Dibenzofuran, and Chlorodibenzo-p-dioxins by Pseudomonas veronii PH-03

The dioxin-degrading strain Pseudomonas veronii PH-03 was isolated from contaminated soil by selective enrichment techniques. Strain PH-03 grew on dibenzo-p-dioxin and dibenzofuran as a sole carbon source. Further, 1-chlorodibenzo-p-dioxin, 2-chlorodibenzo-p-dioxin and other dioxin metabolites, salicylic acid, and catechol were also metabolized well. Resting cells of strain PH-03 transformed dibenzo-p-dioxin, dibenzofuran, 2,2',3-trihydroxybiphenyl, and some chlorodioxins to their corresponding metabolic intermediates such as catechol, salicylic acid, 2-hydroxy-(2-hydroxyphenoxy)-6-oxo-2,4-hexadienoic acid, and chlorocatechols. The formation of these metabolites was confirmed by comparison of gas chromatography-mass spectrometry (GC-MS) data with those of authentic compounds. Although we did observe the production of 3,4,5,6-tetrachlorocatechol (3,4,5,6-TECC) from 1,2,3,4-tetrachlorodibenzo-p-dioxin (1,2,3,4-TCDD) with resting cell suspensions of PH-03, growth of strain PH-03 in the presence of 1,2,3,4-TCDD was poor. This result suggests that strain PH-03 is unable to utilize 3,4,5,6-TECC, even at very low concentration (0.01 mM) due to its toxicity. In cell-free extracts of DF-grown cells, 2,2',3-trihydroxybiphenyl dioxygenase, 2-hydroxy-6-oxo-6-phenyl-2,4-hexadienoic acid hydrolase, and catechol-2,3-dioxygense activities were detected. Moreover, the activities of meta-pyrocatechase and 2,2',3-trihydroxybiphenyl dioxygenase from the crude cell-free extracts were inhibited by 3-chlorocatechol. However, no inhibition was observed in intact cells when 3-chlorocatechol was formed as intermediate.     

Maternal and developmental toxicity of halogenated 4'-nitrodiphenyl ethers in mice

In an ongoing effort to delineate structure-activity relationships in the developmental toxicity of diphenyl ethers, we evaluated the maternal and developmental toxicity of 10 diphenyl ethers related to the herbicide nitrofen. All possible trichlorophenyl 4'-nitrophenyl ethers were evaluated, as were the 2,4-difluorophenyl and 2,4-dibromophenyl 4'-nitrophenyl ethers. We also evaluated bifenox and chlomethoxyfen, which are 2,4-dichlorophenyl congeners with meta-substituents on the 4'-nitrophenyl ring. Nitrofen (2,4-dichlorophenyl 4'-nitrophenyl ether) was included for comparison. Identity of the halogen affected the postnatal (but not prenatal) mortality induced by 2,4-dihalogenated 4'-nitrophenyl ethers. The presence of 3'-substituents on the 4'-nitrophenyl ring reduced both pre- and postnatal toxicity of 2,4-dichlorinated congeners. Among chlorinated 4'-nitrophenyl congeners without meta-substituents on the nitrophenyl ring, the position of chlorine substituents strongly affected the congener's potential for inducing prenatal vs. postnatal syndromes. All congeners increased liver to body weight ratios in unmated females, but such increases were not well-correlated with either prenatal or postnatal embryotoxicity.     

Optimization of the determination of polybrominated diphenyl ethers in human serum using solid-phase extraction and gas chromatography-electron capture negative ionization mass spectrometry

A simple, rapid, sensitive and reproducible method based on solid-phase extraction (SPE) and acidified silica clean-up was developed for the measurement of 12 polybrominated diphenyl ethers (PBDEs), including BDE 209, and 2,2',4,4',5,5'-hexabromobiphenyl (BB 153) in human serum. Several solid-phase sorbents (Empore C(18), Isolute Phenyl, Isolute ENV+ and OASIS HLB) were tested and it was found that OASIStrade mark HLB (500 mg) gives the highest absolute recoveries (between 64% and 95%, R.S.D.<17%, n=3) for all tested analytes and internal standards. Removal of co-extracted biogenic materials was performed using a 6 ml disposable cartridge containing (from bottom to top) silica impregnated with sulphuric acid, activated silica and anhydrous sodium sulphate. PBDEs and BB 153 were quantified using a gas chromatograph coupled with a mass spectrometer (MS) operated in electron-capture negative ionization mode. The method limits of quantification (LOQ) ranged between 0.2 and 25 pg/ml serum (0.1 and 4 ng/g lipid weight). LOQs were dependent on the analyte levels in procedural blanks which resulted in the highest LOQs for PBDE congeners found in higher concentrations in blanks (e.g. BDE 47, 99 and 209). The use of OASIS HLB SPE cartridge allowed a good method repeatability (within- and between-day precision<12% for all congeners, except for BDE 209<17%, n=3). The method was applied to serum samples from a random Belgian population. The obtained results were within the range of PBDE levels in other non-exposed population from Europe.     

Determination and occurrence of polybrominated diphenyl ethers in maternal adipose tissue from inhabitants of Singapore

Polybrominated diphenyl ethers (PBDEs), as a specific group of brominated flame retardants (BFR), are used in a variety of consumer products including electronics and household furnishings. In recent years, a marked increase in the levels of PBDEs in human biological tissues and fluids, especially breast milk, has been reported in several countries. However, few data are available from countries in the Asia-pacific region, including Singapore. This study presents a validated method procedure and the first available data of the concentrations of PBDE congeners: PBDE-47 (2,2,4,4-Tetrabromodiphenyl ether), PBDE-99 (2,2',4,4',5-Pentabromodiphenyl ether), PBDE-100 (2,2',4,4',6-Pentabromodiphenyl ether), PBDE-153 (2,2',4,4',5,5'-Hexabromodiphenyl ether), PBDE-154 (2,2',4,4',5,6'-Hexabromodiphenyl ether) in maternal adipose tissue collected from inhabitants of Singapore. Microwave-assisted extraction (MAE) of PBDEs spiked adipose tissues coupled with GC-MS analysis achieved comparable recoveries to a conventional Soxhlet Extraction (SE) procedure of between 70 and 130%. MAE also yielded comparable precision data (variance less than 13%) relative to the SE procedure. Spiked Carbon-13 PBDE congeners were also used as surrogates for MAE quality assurance and confirmed the efficiency of the procedure. PBDE congeners were detected in all of 16 maternal adipose tissues collected in Singapore, where levels were comparable to available data from Belgium.     

Biomonitoring of polybrominated diphenyl ether (PBDE) pollution: a field study

Polybrominated diphenyl ethers (PBDEs) and cytochrome P450 enzyme activities were investigated in European eels (Anguilla anguilla) collected from seven sites in a coastal lagoon in the north-western Mediterranean Sea, Orbetello lagoon (Italy). Twelve PBDE congeners were measured in muscle and two CYP1A enzyme activities, 7-ethoxyresorufin-O-deethylase (EROD) and benzo(a)pyrene monooxygenase (BP(a)PMO), were investigated in liver microsomal fraction in order to obtain insights into the health of the lagoon environment. PBDE muscle levels were low and the most abundant congeners were 2,2',4,4'-tetrabromodiphenylether (BDE-47), 2,2',4,4',5,5'-hexaBDE (BDE-153) and 2,2',4,5'-tetraBDE (BDE-49). EROD and B(a)PMO activities were also low and no differences were observed between eels from different sites. Multivariate analysis (PCA) did not indicate correlations between PBDEs and either P450 activities.     

In Vitro Effects of Environmentally Relevant Polybrominated Diphenyl Ether (PBDE) Congeners on Calcium Buffering Mechanisms in Rat Brain

Polybrominated diphenyl ethers (PBDEs) are widely used as additive flame-retardants and have been detected in human blood, adipose tissue, and breast milk. Developmental and long-term exposures to these chemicals may pose a human health risk, especially to children. We have previously demonstrated that polychlorinated biphenyls (PCBs), which are structurally similar to PBDEs and cause neurotoxicity, perturb intracellular signaling events including calcium homeostasis and protein kinase C translocation, which are critical for neuronal function and development of the nervous system. The objective of the present study was to test whether environmentally relevant PBDE congeners 47 and 99 are also capable of disrupting Ca^{2 +} homeostasis. Calcium buffering was determined by measuring ⁴⁵Ca^{2 +} -uptake by microsomes and mitochondria, isolated from adult male rat brain (frontal cortex, cerebellum, hippocampus, and hypothalamus). Results show that PBDEs 47 and 99 inhibit both microsomal and mitochondrial ⁴⁵Ca^{2 +} -uptake in a concentration-dependent manner. The effect of these congeners on ⁴⁵Ca^{2 +} -uptake is similar in all four brain regions though the hypothalamus seems to be slightly more sensitive. Among the two preparations, the congeners inhibited ⁴⁵Ca^{2 +} -uptake in mitochondria to a greater extent than in microsomes. These results indicate that PBDE 47 and PBDE 99 congeners perturb calcium signaling in rat brain in a manner similar to PCB congeners, suggesting a common mode of action of these persistent organic pollutants. The research described in this article has been reviewed by the National Health and Environmental Effects Research Laboratory of the US Environmental Protection Agency, and approved for publication. Approval does not signify that the contents necessarily reflect the views and policies of the Agency nor does mention of trade names or commercial products constitute endorsement or recommendation for use. These results will be presented at the 21th Biennial Meeting of International Society for Neurochemistry and American Society for Neurochemistry in Cancun, Mexico (August 19–24, 2007). Special issue article in honor of Dr. Frode Fonnum.     

Binding of hydroxylated polybrominated diphenyl ethers with human serum albumin: Spectroscopic characterization and molecular modeling

Three hydroxylated polybrominated diphenyl ethers (OH‐PBDEs), 3‐OH‐BDE‐47, 5‐OH‐BDE‐47, and 6‐OH‐BDE‐47, were selected to investigate the interactions between OH‐PBDEs with human serum albumin (HSA) under physiological conditions. The observed fluorescence quenching can be attributed to the formation of complexes between HSA and OH‐PBDEs. The thermodynamic parameters at different temperatures indicate that the binding was caused by hydrophobic forces and hydrogen bonds. Molecular modeling and three‐dimensional fluorescence spectrum showed conformational and microenvironmental changes in HSA. Circular dichroism analysis showed that the addition of OH‐PBDEs changed the conformation of HSA with a minor reduction in α‐helix content and increase in β‐sheet content. Furthermore, binding distance r between the donor (HSA) and acceptor (three OH‐PBDEs) calculated using Förster's nonradiative energy transfer theory was <7 nm; therefore, the quenching mechanisms for the binding between HSA and OH‐PBDEs involve static quenching and energy transfer. Combined with molecular dynamics simulations, the binding free energies (ΔG _bind ) were calculated using molecular mechanics/Poisson ? Boltzmann surface area method, and the crucial residues in HSA were identified.     

Evaluation of four capillary columns for the analysis of organochlorine pesticides, polychlorinated biphenyls, and polybrominated diphenyl ethers in human serum for epidemiologic studies

The separation of organochlorine pesticides (OCPs), polychlorinated biphenyls (PCBs), and polybrominated diphenyl ether (PBDE) congeners was evaluated on four capillary columns: 60 m x 0.25 mm i.d., 0.25 microm film thickness RTX-5MS and DB-XLB capillary columns, and 60 m x 0.18 mm i.d., 0.25 microm film thickness DB-XLB and DB-5MS capillary columns. Based on performance, capacity, and cost, the RTX-5MS (60 m x 0.25 mm i.d., 0.25 microm thickness) and the DB-XLB (60 m x 0.25 mm i.d., 0.25 microm film thickness) were selected for the analysis of human serum extracts by using gas chromatography/electron-capture detection. In contrast to previous studies, the oven temperature program affords the separation of congeners that are not separated by using other combinations of capillary columns, most notably PBDE-47 and PCB 180. In addition, the method enables determination of OCPs, PCBs, and PBDEs prevalent in a single extract of serum, which can lead to considerable time savings in the analysis of large number of samples collected for epidemiologic studies.     

Antibacterial Diphenyl Ether,Benzophenone and Xanthone Derivatives from Aspergillus flavipes

The extract of the strain Aspergillus flavipes DL‐11 exerted antibacterial activities against six Gram‐positive bacteria. During the following bioassay‐guided separation, ten diphenyl ethers ( 1 – 10 ), two benzophenones ( 11 – 12 ), together with two xanthones ( 13 – 14 ) were isolated. Among them, 4′‐chloroasterric acid ( 1 ) was a new chlorinated diphenyl ether. Their structures were elucidated by extensive spectroscopic data analysis, including IR, HR‐ESI‐MS, NMR experiments, and by comparison with the literature data. All compounds showed moderate to strong antibacterial effects on different Gram‐positive bacteria with MIC values that ranged from 3.13 to 50 μg/mL, but none of the compounds exhibited activity against Gram‐negative bacteria Vibrio parahaemolyticus ATCC17802 (MIC>100 μg/mL). In particular, the MICs of some compounds are at the level of positive control.     

Reductive Debromination of Polybrominated Diphenyl Ethers by Anaerobic Bacteria from Soils and Sediments

Polybrominated diphenyl ethers (PBDEs) have attracted attention recently due to their proven adverse effects on animals and their increasing concentrations in various environmental media and biota. To gain insight into the fate of PBDEs, microcosms established with soils and sediments from 28 locations were investigated to determine their debromination potential with an octa-brominated diphenyl ether (octa-BDE) mixture consisting of hexa- to nona-BDEs. Debromination occurred in microcosms containing samples from 20 of the 28 locations when they were spiked with octa-BDE dissolved in the solvent trichloroethene (TCE), which is a potential cosubstrate for stimulating PBDE debromination, and in microcosms containing samples from 11 of the 28 locations when they were spiked with octa-BDE dissolved in nonane. Debromination products ranging from hexa- to mono-BDEs were generated within 2 months. Notably, the toxic tetra-BDEs accounted for 50% of the total product. In sediment-free culture C-N-7* amended with the octa-BDE mixture and nonane (containing 45 nM nona-BDE, 181 nM octa-BDEs, 294 nM hepta-BDE, and 19 nM hexa-BDE) there was extensive debromination of the parent compounds, which produced hexa-BDE (56 nM), penta-BDEs (124 nM), and tetra-BDEs (150 nM) within 42 days, possibly by a metabolic process. A 16S rRNA gene-based analysis revealed that Dehalococcoides species were present in 11 of 14 active microcosms. However, unknown debrominating species in some of the microcosms debrominated the octa-BDE mixture in the absence of other added halogenated electron acceptors (such as TCE). These findings provide information that is useful for assessing microbial reductive debromination of higher brominated PBDEs to less-brominated congeners, a possible source of the more toxic congeners (e.g., penta- and tetra-BDEs) detected in the environment.Since they were first developed in the 1960s, polybrominated diphenyl ethers (PBDEs) have been used as flame retardant additives in an array of common household and industrial appliances. As a result of their widespread use, PBDEs have become ubiquitous environmental contaminants, and increasing levels have been detected in the air, soil, and water (5, 12). In a recent study, Leung et al. reported the highest PBDE concentrations in soil samples (2.7 to ∼4.3 ppb) and combusted residues (33.0 to ∼97.4 ppb) that were collected in Guiyu, Guangdong Province, China (18). More worrisome is the fact that increasing concentrations of PBDEs have also been detected in marine mammals, birds, fishes, and human tissues (3, 14, 20, 30), and 63 ppm of PBDEs in bird eggs is the highest level ever found in biota (23). The PBDE concentrations in both environmental samples and biota have been increasing exponentially, with a doubling time of 4 to 6 years (5, 12). Although the PBDEs comprise 209 different congeners designated 1 to 209, the PBDE congeners most often detected in biota (e.g., human tissues) include tetra-brominated diphenyl ether (tetra-BDE) (congener 47), penta-BDEs (congeners 99 and 100), and hexa-BDEs (congeners 153 and 154), which may have originated directly from a commercially available penta-BDE technical mixture or indirectly via breakdown of an octa- or deca-BDE technical mixture (10, 12). PBDEs began to receive worldwide scientific and public attention when a temporal study performed from 1972 to 1997 revealed increasing concentrations of PBDEs in Swedish human breast milk (19). Toxicological studies of rodents using a commercial penta-BDE mixture (including tetra-, penta- and hexa-BDEs) and congeners in a commercial octa-BDE mixture (such as hepta-BDE [congener 183] and octa-BDE [congener 203]) revealed developmental neurotoxicity, reproductive toxicity, liver toxicity, and disruption of thyroid hormone levels (24, 26, 29).To date, studies of PBDEs have focused mainly on detection of these compounds in the environment and their potential adverse health effects; only a few studies have reported microbial debromination of PBDEs (7, 10, 22, 25). Recently, He et al. demonstrated debromination of a technical octa-BDE mixture by pure isolates of Dehalococcoides species, which generated hepta- to di-BDEs after 6 months of incubation (10). Additionally, microbes belonging to the genera Dehalobacter and Desulfitobacterium were also found to be able to debrominate individual PBDE congeners present in commercial octa-BDE mixtures (10, 22). However, the debromination of PBDEs in both studies required the presence of a primary electron acceptor (e.g., chloroethenes or chlorophenols); in other words, debromination occurred cometabolically.In addition to debromination of PBDEs by pure cultures, a previous study demonstrated that in anaerobic sludge 5% of added deca-BDE (congener 209) was debrominated to nona- and octa-BDEs (total amount of product, 0.5 nmol) after 238 days of incubation (7). Moreover, another study showed that deca-BDE was debrominated to products ranging from nona-BDEs to hexa-BDEs in 3.5 years with anaerobic sediments as the inocula (25). These findings suggest that microbial reductive debromination of highly brominated congeners, such as deca-, nona-, octa-, and hepta-BDEs, may contribute to formation of less-brominated PBDEs in the environment, which are potentially more toxic (e.g., tetra- and penta-BDEs). Additionally, debromination of less-brominated PBDE congeners, such as di-BDE, to mono-BDE and diphenyl ether was demonstrated in a fixed-film plug flow biological reactor (21). Besides microbial debromination, highly brominated PBDEs were also found to be transformed to lower congeners via photodegradation or in vivo metabolism in aquatic and terrestrial animals (1, 16).This study was initiated to obtain information about the distribution of microorganisms capable of debrominating highly brominated PBDE congeners to more toxic daughter products or the final product diphenyl ether by assessing microcosm samples collected from various locations. Debromination of an octa-BDE mixture was evaluated in the presence of the potential energy-generating cosubstrate trichloroethene (TCE) (PBDEs dissolved in TCE) or in the presence of the relatively inert solvent nonane (PBDEs dissolved in nonane). The latter experiment provided, for the first time, information about the possible microbes living on the energy generated from the debromination of an octa-BDE mixture in the absence of any cosubstrate, such as TCE or another primer compound. Initial insights into the key debrominating microbes were obtained by using genus-specific 16S rRNA gene-based techniques.     

Degradation of highly chlorinated PCBs byPseudomonas strain LB400

Summary Congeners of polychlorinated biphenyl (PCB) differ in the number and position of chlorine substituents. Although PCBs are degraded, those congoners with five or more chlorines have been considered resistant to bacterial degradation. Metabolism byPseudomonas strain LB400 of PCBs representing a broad spectrum of chlorination patterns and having from two to six chlorines was investigated. Degradation of pure PCB congeners and synthetic congener mixes was measured in resting cell assays with biphenyl- or Luria broth-grown cells. In addition, the appearance of metabolites was followed using HPLC purification, and GC and GC-MS characterization. 2,4,5,2,4,5-[¹⁴C]hexachlorobiphenyl was also used to follow the accumulation of¹⁴C-labeled metabolites. Evidence indicates that LB400 aerobically metabolizes representatives of all major structural classes of PCB's including several congeners which lack adjacent unchlorinated carbon atoms. The mechanisms by which many of these congeners are degraded are not fully understood, but it is apparent that aerobic bacteria can degrade a broader spectrum of PCB congeners than previously believed and that this broad spectrum of degradative competence can exist in a single strain.     

Elevated Serum Polybrominated Diphenyl Ethers and Alteration of Thyroid Hormones in Children from Guiyu,China

Informal electronic waste (e-waste) recycling results in serious environmental pollution of polybrominated diphenyl ethers (PBDEs) and heavy metals. This study explored whether there is an association between PBDEs, heavy metal and key growth- and development-related hormones in children from Guiyu, an e-waste area in southern China. We quantified eight PBDE congeners using gas chromatographic mass spectrometry, lead and cadmium utilizing graphite furnace atomic absorption spectrometry, three thyroids with radioimmunoassay and two types of growth hormones by an enzyme-linked immune-sorbent assay (ELISA) in 162 children, 4 to 6 years old, from Guiyu. In blood, median total PBDE was 189.99 ng/g lipid. Lead and cadmium concentrations in blood averaged 14.53±4.85 µg dL⁻¹ and 0.77±0.35 µg L⁻¹, respectively. Spearman partial correlation analysis illustrated that lead was positively correlated with BDE153 and BDE183. Thyroid-stimulating hormone (TSH) was positively correlated with almost all PBDE congeners and negatively correlated with insulin-like growth factor binding protein-3 (IGFBP-3), whereas free triiodothyronine (FT3) and free thyroxine (FT4) were negatively correlated with BDE154. However, no correlation between the hormones and blood lead or cadmium levels was found in this study. Adjusted multiple linear regression analysis showed that total PBDEs was negatively associated with FT3 and positively associated with TSH. Notably, FT4 was positively correlated with FT3, house functions as a workshop, and father''s work involved in e-waste recycling and negatively correlated with vitamin consumptions. TSH was negatively related with FT4, paternal residence time in Guiyu, working hours of mother, and child bean products intake. IGFBP-3 was positively correlated with IGF-1 and house close to an e-waste dump. These results suggest that elevated PBDEs and heavy metals related to e-waste in Guiyu may be important risk factors for hormone alterations in children.