Anaerobic Microbial Reductive Dehalogenation of Chlorinated Ethenes

The current knowledge on microbial reductive dechlorination of chlorinated ethenes (CEs) and its application are discussed. Physiological studies on CEs dechlorinating microorganisms indicate that a distinction can be made between cometabolic dechlorination and halorespiration. Whereas cometabolic dechlorination is a coincidental and nonspecific side reaction, catalyzed by several methanogenic and acetogenic bacteria, halorespiration is a specific enzymatic reaction from which metabolic energy can be gained. In contrast to the well-studied biological dechlorination of PCE to cis-DCE, little is known about the biology of the further dechlorination from cis-DCE to ethene. Bacteria performing the latter reaction have not yet been isolated. Microbial reductive dechlorination can be applied to the in situ bioremediation of CEs contaminated sites. From laboratory and field studies, it has become clear that the dechlorination of tetrachloroethene (PCE) to cis-clichloroethene (cis-DCE) occurs rapidly and can be stimulated relatively easily. However, complete reduction to ethene appears to be a slower process that is more difficult to achieve.     

Dehalogenation of Chlorinated Hydroxybiphenyls by Fungal Laccase

We have investigated the transformation of chlorinated hydroxybiphenyls by laccase produced by Pycnoporus cinnabarinus. The compounds used were transformed to sparingly water-soluble colored precipitates which were identified by gas chromatography-mass spectrometry as oligomerization products of the chlorinated hydroxybiphenyls. During oligomerization of 2-hydroxy-5-chlorobiphenyl and 3-chloro-4-hydroxybiphenyl, dechlorinated C—C-linked dimers were formed, demonstrating the dehalogenation ability of laccase. In addition to these nonhalogenated dimers, both monohalogenated and dihalogenated dimers were identified.     

Complete Biological Dehalogenation of Chlorinated Ethylenes in Sulfate Containing Groundwater

The ability of dehalogenating bacteria to compete with sulfate reducing bacteria for electron donor was studied in microcosms that simulated groundwater contaminated with both chlorinated ethylenes and fuel hydrocarbon compounds. Results demonstrate that reductive dehalogenation of perchloroethylene to ethylene can proceed in the presence of > 100 mg l(-1) sulfate. The hydrogen concentration, which was 2.5 nM in the presence of approximately 150 mg l(-1) sulfate and in the absence of chlorinated compounds, decreased to 0.7 nM during the dechlorination of trichloroethylene and increased to 1.6 nM during the dechlorination of cis-dichloroethylene and vinyl chloride. With only sediment associated donor ("historical" donor) present, dechlorination of trichloroethylene proceeded slowly to ethylene (on a time scale of several years). Addition of toluene, a model hydrocarbon compound, stimulated dechlorination indirectly. Toluene degradation was rapid and linked to sulfate utilization, and presumably formed fermentable substrates that served as hydrogen donors. Dehalogenation was inhibited in soil free microcosms containing 5 mM sulfide, but inhibition was not observed when either aquifer sediment or 5 mM ferrous chloride was added.     

Reductive Dehalogenation of Chlorinated Benzenes and Toluenes under Methanogenic Conditions

[This corrects the article on p. 3270 in vol. 59.].     

Microbial Destructors of Certain Chlorinated Organics

The possibility of isolation of microorganisms, which are potential destructors of chlorinated organics, from aged Vietnamese soils polluted with dioxine-containing defoliants was demonstrated. As an example, the ability of one isolated strain to metabolize pentachlorophenol and 2,4-dichlorophenoxyacetic acid was shown under laboratory conditions. An attempt was made to identify intermediates of pentachlorophenol metabolism using HPLC.     

Kinetics of Microbial Dehalogenation of Haloaromatic Substrates in Methanogenic Environments

The kinetic parameters associated with the microbial dehalogenation of 3-chlorobenzoate, 3,5-dichlorobenzoate, and 4-amino-3,5-dichlorobenzoate were measured in anoxic sediment slurries and in an enriched methanogenic culture grown on 3-chlorobenzoate. The initial dehalogenation of the substrates exhibited Michaelis-Menten kinetics. The apparent K_m values for the above substrates ranged from 30 to 67 μM. The pattern of degradation, however, was unusual. The enrichment culture accumulated partially dehalogenated intermediates to 72 and 98% of that possible when incubated with either 3,5-dichloro- or 4-amino-3,5-dichlorobenzoate, respectively, but did not accumulate significant amounts of benzoate when 3-chlorobenzoate was the sole carbon and energy source. The accumulated intermediates were rapidly metabolized only after the parent substrate concentrations were nearly depleted (<5 μM). A sequential Michaelis-Menten model was developed to account for the observed pattern of biodegradation. Using this model, we found that relative differences in the K_m and V_max parameters for substrate and intermediate dehalogenations alone were insufficient to explain the transitory accumulation of intermediates. However, by inserting a competitive inhibition term, with the primary substrate as the inhibitor, the observed pattern of degradation was simulated. Apparently, the dichlorinated substrates competitively inhibit the dehalogenation of the monochlorinated substrates. Similar kinetic patterns were noted for sediments, although the rates were slower than in the enrichment culture.     

Microbial Transformation of Esters of Chlorinated Carboxylic Acids

Two groups of compounds were selected for microbial transformation studies. In the first group were carboxylic acid esters having a fixed aromatic moiety and an increasing length of the alkyl component. Ethyl esters of chlorine-substituted carboxylic acids were in the second group. Microorganisms from environmental waters and a pure culture of Pseudomonas putida U were used. The bacterial populations were monitored by plate counts, and disappearance of the parent compound was followed by gas-liquid chromatography as a function of time. The products of microbial hydrolysis were the respective carboxylic acids. Octanol-water partition coefficients (K_ow) for the compounds were measured. These values spanned three orders of magnitude, whereas microbial transformation rate constants (k_b) varied only 50-fold. The microbial rate constants of the carboxylic acid esters with a fixed aromatic moiety increased with an increasing length of alkyl substituents. The regression coefficient for the linear relationships between log k_b and log K_ow was high for group 1 compounds, indicating that these parameters correlated well. The regression coefficient for the linear relationships for group 2 compounds, however, was low, indicating that these parameters correlated poorly.     

Ascertaining the Effect of Reductive Dehalogenation on Chlorinated Hydrocarbon Plume Lengths in Groundwater: Analyses of Multisite Data

Chlorinated hydrocarbon groundwater plume data from a multisite study were evaluated by a variety of statistical techniques (correlation, analysis of covariance, principal components) to quantify the effects of biotransformations (reductive dehalogenation) on plume length. After accounting for the effects of groundwater velocity, source strength, and biases in the data collection process, chlorinated hydrocarbon plume lengths at sites where reductive dehalogenation was occurring were found to be significantly shorter on average, by roughly a factor of two, than those where it was not. Moreover, principal component analyses indicated significant differences in the behavior of chlorinated hydrocarbon plumes between sites with and without evidence of reductive dehalogenation, respectively. The advantage in examining plume behavior from this population-oriented perspective is that overall trends in plume behavior can be evaluated despite site-specific influences such as heterogeneities and unique release histories. Ultimately, it is these average trends that would be of the most interest to policymakers because they represent the ranges of conditions that will be encountered. This is especially important in the case of chlorinated hydrocarbons because they will biotransform at rates significant for appreciable natural attenuation only in certain instances.     

A Novel Hydrolytic Dehalogenase for the Chlorinated Aromatic Compound Chlorothalonil

Dehalogenases play key roles in the detoxification of halogenated aromatics. Interestingly, only one hydrolytic dehalogenase for halogenated aromatics, 4-chlorobenzoyl-coenzyme A (CoA) dehalogenase, has been reported. Here, we characterize another novel hydrolytic dehalogenase for a halogenated aromatic compound from the 2,4,5,6-tetrachloroisophthalonitrile (chlorothalonil)-degrading strain of Pseudomonas sp. CTN-3, which we have named Chd. Chd catalyzes a hydroxyl substitution at the 4-chlorine atom of chlorothalonil. The metabolite of the Chd dehalogenation, 4-hydroxy-trichloroisophthalonitrile, was identified by reverse-phase high-performance liquid chromatography (HPLC), tandem mass spectrometry (MS/MS), and nuclear magnetic resonance (NMR). Chd dehalogenates chlorothalonil under anaerobic and aerobic conditions and does not require the presence of cofactors such as CoA and ATP. Chd contains a putative conserved domain of the metallo-β-lactamase superfamily and shows the highest identity with several metallohydrolases (24 to 29%). Chd is a monomer (36 kDa), and the isoelectric point (pI) of Chd is estimated to be 4.13. Chd has a dissociation constant (K_m) of 0.112 mM and an overall catalytic rate (k_cat) of 207 s⁻¹ for chlorothalonil. Chd is completely inhibited by 1,10-phenanthroline, diethyl pyrocarbonate, and N-bromosuccinic acid. Site-directed mutagenesis of Chd revealed that histidines 128 and 157, serine 126, aspartates 45, 130 and 184, and tryptophan 241 were essential for the dehalogenase activity. Chd differs from other reported hydrolytic dehalogenases based on the analysis of amino acid sequences and catalytic mechanisms. This study provides an excellent dehalogenase candidate for mechanistic study of hydrolytic dehalogenation of halogenated aromatic compound.Halogenated aromatic compounds are widely used in agriculture and industry as solvents, defatting agents, herbicides, and fungicides. A variety of these compounds have been identified as priority organic pollutants by the United Nations and the U.S. Environmental Protection Agency. Therefore, the remediation of these pollutants is desirable. Microorganisms play key roles in the detoxification of halogenated aromatics. The use of microbial enzymes for bioremediation has received increasing attention as an efficient and cost-effective biotechnological approach. Halogen removal from halogenated aromatics reduces both the recalcitrance to biodegradation and the risk of forming toxic intermediates during subsequent metabolic steps. As a result, the key reaction for microbial detoxification of halogenated aromatics is the actual dehalogenation (35).Investigation of the microbial degradation of different halogenated aromatics has led to the detection and elucidation of various dehalogenases that catalyze the removal of the halogen atom under aerobic and anaerobic conditions (8, 11, 17). Four dehalogenation mechanisms of halogenated aromatics are known, including reductive, thiolytic, oxidative, and hydrolytic mechanisms (41). Reductive dehalogenation plays important roles in the degradation of chlorinated aromatics under anaerobic conditions (36, 44). Several anaerobic bacteria are capable of using chlorinated benzenes (2) or polychlorinated dibenzodioxins (5) as the terminal electron acceptors in their energy metabolism. These bacteria couple reductive dehalogenation to electron transport phosphorylation (15). Several enzymes catalyzing the respiratory reductive dechlorination of halogenated aromatics have also been characterized (1, 4, 7, 20, 28, 38, 40). Under aerobic conditions, some chlorinated aromatics can also be reductively dehalogenated by thiolytic substitution in the presence of glutathione (12, 19, 25, 46, 48). In this dehalogenation system, chlorine atoms are displaced by the nucleophilic attack of the thiolate anion of glutathione. The nucleophilic attack of the thiolate anion is catalyzed by glutathione S-transferases (43). Besides the two well-characterized mechanisms for aryl halide reductive dehalogenation, two other mechanisms have been reported, including reduced NADPH-dependent reductive dechlorination of 2,4-dichlorobenzoyl-coenzyme A (CoA) to 4-chlorobenzoyl-CoA in Corynebacterium sepedonicum KZ-4 and coryneform bacterium strain NTB-1 (31), as well as a CoA-mediated reductive dehalogenation of 3-chlorobenzoate in Rhodopseudomonas palustris RCB100 using 3-chlorobenzoate as the carbon source rather than as a terminal electron acceptor (13). Oxidative dehalogenation of halogenated aromatics is catalyzed by monooxygenase (29), dioxygenases (34, 37, 39, 45), and peroxidase (30).Even though several hydrolytic dehalogenases involved in dehalogenation of halogenated aliphatic hydrocarbons and halogenated carboxylic acids have been characterized, only one kind of hydrolytic dehalogenase for halogenated aromatics has been reported. The only hydrolytic dehalogenase identified to date is 4-chlorobenzoyl-CoA dehalogenase in the 4-chlorobenzoate degradation system (32, 33). For the hydrolytic substitution of the chlorine atom of 4-chlorobenzoate with a hydroxyl group, activation by the CoA thioester formation is required. Initially, 4-chlorobenzoate-CoA ligase adenylates the carboxyl group in a reaction requiring ATP, followed by the replacement of AMP with CoA and the formation of a thioester. This intermediate is sufficiently energized to facilitate the replacement of the hydroxyl group with a 4-chlorine atom; this is catalyzed by 4-chlorobenzoyl-CoA dehalogenase. Finally, 4-hydroxybenzoyl-CoA thioesterase removes the CoA (Fig. ​(Fig.1a).1a). Three separate enzymes are involved in this system, and cofactors including CoA and ATP are needed (32, 33).Open in a separate windowFIG. 1.Dechlorination mechanism of 4-chlorobenzoate in Pseudomonas sp. CBS3 and Acinetobacter sp. strain 4-CB1 (a) and the first-step dechlorination mechanism of 2,4,5,6-tetrachloroisophthalonitrile (chlorothalonil) in Pseudomonas sp. CTN-3 (b).Chlorothalonil (2,4,5,6-tetrachloroisophthalonitrile), a broad-spectrum chlorinated aromatic fungicide, is the second most widely used agricultural fungicide in the United States, with 5 million kilograms applied annually (9). Chlorothalonil is highly toxic to fish, birds, and aquatic invertebrates (6) and is commonly detected in ecosystems (18). The bacterial strain Pseudomonas sp. CTN-3, capable of efficiently transforming chlorothalonil, was isolated in our laboratory from long-term chlorothalonil-contaminated soil in the Jiangsu Province in China. In Ochrobactrum anthropi SH35B, a glutathione-dependent glutathione S-transferase was reported to be able to catalyze the nucleophilic substitution of chlorine atoms of chlorothalonil (19). The glutathione S-transferase in our CTN-3 bacterial strain showed 84% identity with that of O. anthropi SH35B. However, the glutathione S-transferase from CTN-3 was not functionally expressed. Here, we report for the first time the characterization of a novel chlorothalonil hydrolytic dehalogenase (Chd) that contains a conserved domain of the metallo-β-lactamase superfamily. Chd is the second hydrolytic dehalogenase for chlorinated aromatic compounds to be identified. The hydrolytic dehalogenation of chlorothalonil catalyzed by Chd is independent of CoA and ATP. Based on the analysis of amino acid sequences and catalytic mechanisms, Chd is unique from the other reported hydrolytic dehalogenases.     

Brominated Biphenyls Prime Extensive Microbial Reductive Dehalogenation of Aroclor 1260 in Housatonic River Sediment

The upper Housatonic River and Woods Pond (Lenox, Mass.), a shallow impoundment on the river, are contaminated with polychlorinated biphenyls (PCBs), the residue of partially dechlorinated Aroclor 1260. Certain PCB congeners have the ability to activate or “prime” anaerobic microorganisms in Woods Pond sediment to reductively dehalogenate the Aroclor 1260 residue. We proposed that brominated biphenyls might have the same effect and tested the priming activities of 14 mono-, di-, and tribrominated biphenyls (350 μM) in anaerobic microcosms of sediment from Woods Pond. All of the brominated biphenyls were completely dehalogenated to biphenyl, and 13 of them primed PCB dechlorination. Measured in terms of chlorine removal and decrease in the proportion of hexa- through nonachlorobiphenyls, the microbial PCB dechlorination primed by several brominated biphenyls was nearly twice as effective as that primed by chlorinated biphenyls. Congeners containing a meta bromine primed Dechlorination Process N (flanked meta dechlorination), and congeners containing an unflanked para bromine primed Dechlorination Process P (flanked para dechlorination). Two ortho-substituted congeners, 2-bromobiphenyl and 2,6-dibromobiphenyl (2-BB and 26-BB), also primed Process N dechlorination. The most effective primers were 26-BB, 245-BB, 25-3-BB, and 25-4-BB. The microbial dechlorination primed by 26-BB converted ~75% of the hexa- through nonachlorobiphenyls to tri- and tetrachlorobiphenyls in 100 days and removed ~75% of the PCBs that are most persistent in humans. These results represent a major step toward identifying an effective method for accelerating PCB dechlorination in situ. The challenge now is to identify naturally occurring compounds that are safe and effective primers.     

Reductive Dehalogenation and Conversion of 2-Chlorophenol to 3-Chlorobenzoate in a Methanogenic Sediment Community: Implications for Predicting the Environmental Fate of Chlorinated Pollutants

Biotransformation of 2-chlorophenol by a methanogenic sediment community resulted in the transient accumulation of phenol and benzoate. 3-Chlorobenzoate was a more persistent product of 2-chlorophenol metabolism. The anaerobic biotransformation of phenol to benzoate presumably occurred via para-carboxylation and dehydroxylation reactions, which may also explain the observed conversion of 2-chlorophenol to 3-chlorobenzoate.     

Microbial Consortia for Hydrogen Production Enhancement

Ten efficient hydrogen-producing strains affiliated to the Clostridium genus were used to develop consortia for hydrogen production. In order to determine their saccharolytic and proteolytic activities, glucose and meat extract were tested as fermentation substrates, and the best hydrogen-producing strains were selected. The C. roseum H5 (glucose-consuming) and C. butyricum R4 (protein-degrading) co-culture was the best hydrogen-producing co-culture. The end-fermentation products for the axenic cultures and co-cultures were analyzed. In all cases, organic acids, mainly butyrate and acetate, were produced lowering the pH and thus inhibiting further hydrogen production. In order to replace the need for reducing agents for the anaerobic growth of clostridia, a microbial consortium including Clostridium spp. and an oxygen-consuming microorganism able to form dense granules (Streptomyces sp.) was created. Increased yields of hydrogen were achieved. The effect of adding a butyrate-degrading bacteria and an acetate-consuming archaea to the consortia was also studied.     

Microbial Growth on Dichlorobiphenyls Chlorinated on Both Rings as a Sole Carbon and Energy Source

We have isolated bacterial strains capable of aerobic growth on ortho-substituted dichlorobiphenyls as sole carbon and energy sources. During growth on 2,2′-dichlorobiphenyl and 2,4′-dichlorobiphenyl strain SK-4 produced stoichiometric amounts of 2-chlorobenzoate and 4-chlorobenzoate, respectively. Chlorobenzoates were not produced when strain SK-3 was grown on 2,4′-dichlorobiphenyl.     

Modeling Chlorinated Solvent Bioremediation Using Hydrogen Release Compound (HRC)

Chlorinated solvents such as tetrachloroethene (PCE) and trichloroethene (TCE) are common groundwater contaminants. One approach that has been used to manage these contaminants is in situ bioremediation, where an electron donor is added to contaminated groundwater to stimulate indigenous bacteria to degrade the chlorinated compounds. A technique that is increasingly being used to supply electron donor to the subsurface involves application of a commercial product with the trade name Hydrogen Release Compound (HRC). HRC is a viscous fluid that releases lactic acid, which subsequently is metabolized to provide molecular hydrogen as an electron donor. This study investigates application of HRC to remediate a site contaminated with TCE. A user-defined dual-Monod biodegradation reaction module was developed for the RT3D-reactive transport code to simulate in situ biodegradation of TCE by reductive dehalogenation stimulated by release of molecular hydrogen in the subsurface as a result of HRC injection. The model was used to show how a remediation system using HRC to stimulate reductive dehalogenation could be designed, and how mixing, as quantified by hydraulic conductivity and dispersivity, impacts the system design.     

新型复合型生物絮凝剂的制备与应用研究

目的:为了得到高效实用的复合型微生物絮凝剂.方法:利用甘蔗渣作为廉价底物,进行复发酵培养:前期为3d,后期为1d,温度为30℃;初始pH值为7.2;同时以珠江河水作为实验水源,对其性能进行研究.结果:复合型微生物絮凝剂对水的浊度、色度去除最佳投加量为12mL/L,同时考虑到其实际使用,制成含水率为80%左右的干粉,试验其对水中TP、邻苯二甲酸脂的去除效果,其最佳投加量为0.21 mg/L.     

Microbial Anaerobic Demethylation and Dechlorination of Chlorinated Hydroquinone Metabolites Synthesized by Basidiomycete Fungi

The synthesis and degradation of anthropogenic and natural organohalides are the basis of a global halogen cycle. Chlorinated hydroquinone metabolites (CHMs) synthesized by basidiomycete fungi and present in wetland and forest soil are constituents of that cycle. Anaerobic dehalogenating bacteria coexist with basidiomycete fungi in soils and sediments, but little is known about the fate of these halogenated fungal compounds. In sediment microcosms, the CHMs 2,3,5,6-tetrachloro-1,4-dimethoxybenzene and 2,3,5,6-tetrachloro-4-methoxyphenol (TCMP) were anaerobically demethylated to tetrachlorohydroquinone (TCHQ). Subsequently, TCHQ was converted to trichlorohydroquinone and 2,5-dichlorohydroquinone (2,5-DCHQ) in freshwater and estuarine enrichment cultures. Screening of several dehalogenating bacteria revealed that Desulfitobacterium hafniense strains DCB2 and PCP1, Desulfitobacterium chlororespirans strain Co23, and Desulfitobacterium dehalogenans JW/DU1 sequentially dechlorinate TCMP to 2,3,5-trichloro-4-methoxyphenol and 3,5-dichloro-4-methoxyphenol (3,5-DCMP). After a lag, these strains demethylate 3,5-DCMP to 2,6-DCHQ, which is then completely dechlorinated to 1,4-dihydroquinone (HQ). 2,5-DCHQ accumulated as an intermediate during the dechlorination of TCHQ to HQ by the TCMP-degrading desulfitobacteria. HQ accumulation following TCMP or TCHQ dechlorination was transient and became undetectable after 14 days, which suggests mineralization of the fungal compounds. This is the first report on the anaerobic degradation of fungal CHMs, and it establishes a fundamental role for microbial reductive degradation of natural organochlorides in the global halogen cycle.     

Dehalogenation of 4-chlorobenzoate

Pseudomonas sp. CBS3 is capable of growing with 4-chlorobenzoate as sole source of carbon and energy. The removal of the chlorine of 4-chlorobenzoate is performed in the first degradation step by an enzyme system consisting of three proteins. A 4-halobenzoate-coenzyme A ligase activates 4-chlorobenzoate in a coenzyme A, ATP and Mg²⁺ dependent reaction to 4-chlorobenzoyl-coenzyme A. This thioester intermediate is dehalogenated by the 4-chlorobenzoyl-coenzyme A dehalogenase. Finally coenzyme A is split off by a 4-hydroxybenzoyl-CoA thioesterase to form 4-hydroxybenzoate. The involved 4-chlorobenzoyl-coenzyme A dehalogenase was purified to apparent homogeneity by a five-step purification procedure. The native enzyme had an apparent molecular mass of 120,000 and was composed of four identical polypeptide subunits of 31 kDa. The enzyme displayed an isoelectric point of 6.7. The maximal initial rate of catalysis was achieved at pH 10 at 60 °C. The apparent K _m value for 4-chlorobenzoyl-coenzyme A was 2.4–2.7 µM. V _max was 1.1 × 10^–7 M sec^–1 (2.2 µmol min^–1 mg^–1 of protein). The NH₂-terminal amino acid sequence was determined. All 4-halobenzoyl-coenzyme A thioesters, except 4-fluorobenzoyl-coenzyme A, were dehalogenated by the 4-chlorobenzoyl-CoA dehalogenase.Abbreviations CBA chlorobenzoate - CoA coenzyme A - HBA hydroxybenzoate - DTT dithiothreitol - HPLC high performance liquid chromatography - PAGE polyacrylamide gel electrophoresis     

Microbial Stabilization and Kinetic Enhancement of Marine Methane Hydrates

Abstract

In clathrate hydrates, a water host lattice encages small guest molecules in cavities. Methane hydrates are the most widespread in-situ clathrate in the permafrost and continental-shelf ocean regions, constituting a significant energy resource, and prompting recent marine-hydrate gas-production trials. Despite exciting engineering advances and a few marine-mimicking laboratory studies of methane-hydrate kinetics and stabilization, from microbial perspectives, little is known about a potential microbial origin of marine hydrates, nor their possible formation kinetics or potential stabilization by microbial sources. Here, for the first time, we show that an exported, extra-cytoplasmic porin – produced by a marine methylotrophic bacterium culture – provides the basis for kinetic enhancement and stabilization of methane hydrates under conditions simulating the seabed environment. We then identify the key protein at play, and we therefore suggest microbe-based stabilization of marine hydrates is evidently a property likely to be found in many marine bacteria. Our research opens the possibility of managing marine-hydrate deposits using microbiological strategies for environmental and societal benefit.     

Characterization of a Microbial Consortium Capable of Rapid and Simultaneous Dechlorination of 1,1,2,2-Tetrachloroethane and Chlorinated Ethane and Ethene Intermediates

Mixed cultures capable of dechlorinating chlorinated ethanes and ethenes were enriched from contaminated wetland sediment at Aberdeen Proving Ground (APG) Maryland. The “West Branch Consortium” (WBC-2) was capable of degrading 1,1,2,2-tetrachloroethane (TeCA), trichloroethene (TCE), cis and trans 1,2-dichloroethene (DCE), 1,1,2-trichloroethane (TCA), 1,2-dichloroethane, and vinyl chloride to nonchlorinated end products ethene and ethane. WBC-2 dechlorinated TeCA, TCA, and cisDCE rapidly and simultaneously. A Clostridium sp. phylogenetically closely related to an uncultured member of a TCE-degrading consortium was numerically dominant in the WBC-2 clone library after 11 months of enrichment in culture. Clostridiales, including Acetobacteria, comprised 65% of the bacterial clones in WBC-2, with Bacteroides (14%), and epsilon Proteobacteria (14%) also numerically important. Methanogens identified in the consortium were members of the class Methanomicrobia, which includes acetoclastic methanogens. Dehalococcoides did not become dominant in the culture, although it was present at about 1% in the microbial population. The WBC-2 consortium provides opportunities for the in situ bioremediation of sites contaminated with mixtures of chlorinated ethenes and ethanes.     

Dehalogenation of lindane by a variety of porphyrins and corrins

The dehalogenation of lindane by a range of hemoproteins, porphyrins, and corrins has been tested under reducing conditions in the presence of dithiothreitol. In addition, a series of porphyrin-metal ion complexes have been prepared and have also been screened for the capacity to dehalogenate lindane. Hemoglobin, hemin, hematin, and chlorophyll alpha all catalyzed the dehalogenation of lindane, as did all of the corrins tested. The porphyrins which did not contain metal centers--coproporphyrin, hematoporphyrin, protoporphyrin, and uroporphyrin--were inactive. However, when these porphyrins were then complexed with Co, Fe, Mg, Mo, Ni, or V, lindane dehalogenation was observed. In all cases, the reaction proceeded by an initial dechlorination to produce tetrachlorocyclohexene, which was further dehalogenated to yield chlorobenzene as the end product.