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Query: EC:3.4.23.17 (PCE)
 1,301 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Reductive dehalogenation of tetrachloroethene (PCE), trichloroethene (TCE), cis-1,2-dichloroethene (DCE), and vinyl chloride (VC) was examined in four cultures containing Dehalococcoides-like microorganisms. Dechlorination and growth kinetics were compared using a Monod growth-rate model for multiple electron acceptor usage with competition. Included were the Victoria mixed culture containing Dehalococcoides species strain VS (from Victoria, TX), the mixed culture KB-1/VC (from southern Ontario), the Pinellas mixed culture (from Pinellas, FL), and D. ethenogenes strain 195. All cultures, with the exception of D. ethenogenes strain 195, grew with VC as catabolic electron acceptor. A dilution method was developed that allows a valid comparison to be made of dehalogenating kinetics between different mixed cultures. Using this procedure, maximum growth rates on VC were found to be similar for strain VS and KB-1/VC (0.42-0.49 +/- 0.02 d(-1)) but slower for the Pinellas culture (0.28 +/- 0.01 d(-1)). The 16S rRNA gene sequences were determined to ensure that no cross contamination between cultures had occurred. Following enrichment of the VC dechlorinating microorganisms on VC, the cultures were amended with DCE, TCE, or PCE. The three mixed cultures failed to dechlorinate PCE or did so very slowly. However, the dilution technique indicated that all experienced growth on TCE and DCE as well as on VC. Maximum growth rates on DCE alone were quite similar (0.43-0.46 d(-1)), while the Pinellas culture grew faster on TCE alone (0.49 d(-1)) than did the other two mixed cultures (0.33-0.35 d(-1)). Half-velocity and inhibition constants for growth on TCE were also determined for the three mixed cultures; both constants were found to be essentially equal and the same for the different cultures, varying between only 8.6 and 10.5 microM. The ability of the strain VS, KB-1/VC, and Pinellas cultures to utilize TCE rapidly with conversion to ethene is quite different from that of any other reported microorganism. It was separately confirmed with more traditional cell-counting techniques that strain VS coupled TCE, as well as DCE and VC, utilization with growth. This is the first report of an organism obtaining energy for growth through every step in the reduction of TCE to ethene. Also, as suggested by the dilution technique, the dehalogenating organisms in the KB-1/VC and Pinellas cultures appear to obtain growth from TCE utilization as well. Such ability to grow while dehalogenating TCE to ethene will be an important advantage for their use in bioaugmentation.
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PMID:Comparative evaluation of chloroethene dechlorination to ethene by Dehalococcoides-like microorganisms. 1548 86

A microcosm study was used to assess the potential for in situ natural or enhanced bioremediation at a chloroethane- (i.e., tetrachloroethane, TeCA) and chloroethene-contaminated (i.e., tetrachloroethene, PCE; trichloroethene, TCE) groundwater in Northern Italy. All the live microcosms were positive for dechlorination, indicating the presence of an active native dechlorinating population in the subsurface. All the tested electron donors (i.e., yeast extract, lactate, butyrate, hydrogen) promoted enhanced dechlorination of chlorinated contaminants. Lactate- and butyrate-amended microcosms performed the best, and also dechlorinated the solvents past cis-dichloroethene (cis-DCE). The microcosm bioaugmented with a PCE-dechlorinating mixed culture containing Dehalococcoides spp. dechlorinated groundwater contaminants to DCE, vinyl chloride (VC), and ethene (ETH). In conclusion, results from this microcosm study indicate the potential for enhancing full dechlorination at the contaminated site, through a proper addition of a suitable electron donor (e.g., lactate or butyrate) and/or through bioaugmentation with a Dehalococcoides-containing culture.
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PMID:Assessment of natural or enhanced in situ bioremediation at a chlorinated solvent-contaminated aquifer in Italy: a microcosm study. 1566 Dec 81

Kinetic studies with two different anaerobic mixed cultures (the PM and the EV cultures) were conducted to evaluate inhibition between chlorinated ethylenes. The more chlorinated ethylenes inhibited the reductive dechlorination of the less chlorinated ethylenes, while the less chlorinated ethylenes weakly inhibited the dechlorination of the more chlorinated ethylenes. Tetrachloroethylene (PCE) inhibited reductive trichloroethylene (TCE) dechlorination but not cis-dichloroethylene (c-DCE) dechlorination, while TCE strongly inhibited c-DCE and VC dechlorination. c-DCE also inhibited vinyl chloride (VC) transformation to ethylene (ETH). When a competitive inhibition model was applied, the inhibition constant (K(I)) for the more chlorinated ethylene was comparable to its respective Michaelis-Menten half-velocity coefficient, K(S). Model simulations using independently derived kinetic parameters matched the experimental results well. k(max) and K(S) values required for model simulations of anaerobic dechlorination reactions were obtained using a multiple equilibration method conducted in a single reactor. The method provided precise kinetic values for each step of the dechlorination process. The greatest difference in kinetic parameters was for the VC transformation step. VC was transformed more slowly by the PM culture (k(max) and K(S) values of 2.4+/-0.4 micromol/mg of protein/day and 602+/-7 microM, respectively) compared to the EV culture (8.1+/-0.9 micromol/mg of protein/day and 62.6+/-2.4 microM). Experimental results and model simulations both illustrate how low K(S) values corresponded to efficient reductive dechlorination for the more highly chlorinated ethylenes but caused strong inhibition of the transformation of the less chlorinated products. Thus, obtaining accurate K(S) values is important for modeling both transformation rates of parent compounds and their inhibition on daughter product transformation.
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PMID:Kinetics and inhibition of reductive dechlorination of chlorinated ethylenes by two different mixed cultures. 1566 95

Dehalococcoides ethenogenes strain 195 reductively dechlorinates tetrachloroethene (PCE) and trichloroethene (TCE) to vinyl chloride and ethene using H2 as an electron donor. PCE- and TCE-reductive dehalogenase (RD) activities were mainly membrane associated, whereas only about 20% of the hydrogenase activity was membrane associated. Experiments with methyl viologen (MV) were consistent with a periplasmic location for the RDs or a component feeding electrons to them. The protonophore uncoupler tetrachlorosalicylanilide did not inhibit reductive dechlorination in cells incubated with H2 and PCE and partially restored activity in cells incubated with the ATPase inhibitor N,N'-dicyclohexylcarbodiimide. Benzyl viologen or diquat (Eo' approximately -360 mV) supported reductive dechlorination of PCE or TCE at rates comparable to MV (-450 mV) in cell extracts.
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PMID:Characterization of hydrogenase and reductive dehalogenase activities of Dehalococcoides ethenogenes strain 195. 1574 76

A strictly anaerobic bacterium was isolated from tetrachloroethene (PCE)-to-ethene dechlorinating microcosms established with river sediment without prior exposure to chlorinated solvents. The isolation procedure included the addition of 2-bromoethanesulfonate to select against methanogenic archaea, >50 consecutive 1-2% (v/v) transfers to reduced mineral salts medium amended with trichloroethene (TCE), acetate, and hydrogen, the addition of ampicillin, and the dilution-to-extinction principle. Culture-dependent and 16S rRNA gene-targeted approaches suggested culture purity. Microscopic examination revealed a homogeneous culture of an organism with a distinct, disc-shaped morphology. The isolate shared >99% 16S rRNA gene sequence similarity with members of the Pinellas group of the Dehalococcoides cluster, and was designated Dehalococcoides sp. strain FL2. Strain FL2 could be propagated with TCE, cis-1,2-dichloroethene (cis-DCE), or trans-DCE as the electron acceptors, acetate as the carbon source, and hydrogen as the electron donor in defined, completely synthetic medium. No other growth-supporting redox couples were identified. Trichloroethene, cis-DCE and trans-DCE were dechlorinated at rates of 27.5, 30.4 and 18.8 micromol l-1 day-1 respectively. Quantitative real-time polymerase chain reaction (PCR) with a fluorescently labelled linear hybridization probe confirmed growth with these electron acceptors, and suggested that strain FL2 captures energy from both the TCE-to-cis-DCE and 1,2-DCE-to-VC dechlorination steps. Tetrachloroethene and vinyl chloride (VC) were slowly and cometabolically dechlorinated in the presence of a growth-supporting chloroethene, but ethene formation was incomplete, even after prolonged incubation. At room temperature, strain FL2 grew with a doubling time of 2.4 days, and yielded 166.1+/-10.2 mg of protein per mole of chloride released. In the presence of excess electron acceptor, strain FL2 consumed hydrogen to a concentration of 0.061+/-0.016 nM. Dechlorination ceased following the addition of 0.5 mM sulfite, whereas sulfate (10 mM) and nitrate (5 mM) had no inhibitory effects.
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PMID:Isolation and characterization of Dehalococcoides sp. strain FL2, a trichloroethene (TCE)- and 1,2-dichloroethene-respiring anaerobe. 1610 66

The demonstration of monitored natural attenuation (MNA) of chlorinated hydrocarbons in groundwater is typically conducted through the evaluation of concentration trends and parent-daughter product relationships along prevailing groundwater flow paths. Unfortunately, at sites contaminated by mixtures of chlorinated ethenes, ethanes, and methanes, the evaluation of MNA by using solely concentration data and parent-daughter relationships can result in erroneous conclusions regarding the degradation mechanisms that are truly active at the site, since many of the daughter products can be derived from multiple parent compounds. Stable carbon isotope analysis was used, in conjunction with concentration data, to clarify and confirm the active degradation pathways at a former waste solvent disposal site where at least 14 different chlorinated hydrocarbons have been detected in the groundwater. The isotope data indicate that TCE, initially believed to be present as a disposed product and/or a PCE dechlorination intermediate, is attributable to dehydrochlorination of 1,1,2,2-PCA. The isotope data further support that vinyl chloride and ethene in the site groundwater result from dichloroelimination of 1,1,2-trichlorethane and 1,2-dichloroethane, respectively, rather than from reductive dechlorination of the chlorinated ethenes PCE, TCE, or 1,2-DCE. The isotope data confirm that the chlorinated ethanes and chlorinated methanes are undergoing significant intrinsic degradation, whereas degradation of the chlorinated ethenes may be limited. In addition to the classical trend of enriched isotope values of the parent compounds with increasing distance associated to biodegradation, shifts of isotope ratios of degradation byproduct in the opposite direction due to mixing of isotopically light byproducts of biodegradation with compounds from the source are shown to be of high diagnostic value. These data underline the value of stable isotope analysis in confirming transformation processes at sites with complex mixtures of chlorinated compounds.
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PMID:Assessment of degradation pathways in an aquifer with mixed chlorinated hydrocarbon contamination using stable isotope analysis. 1617 53

A novel Dehalococcoides isolate capable of metabolic trichloroethene (TCE)-to-ethene reductive dechlorination was obtained from contaminated aquifer material. Growth studies and 16S rRNA gene-targeted analyses suggested culture purity; however, the careful quantitative analysis of Dehalococcoides 16S rRNA gene and chloroethene reductive dehalogenase gene (i.e., vcrA, tceA, and bvcA) copy numbers revealed that the culture consisted of multiple, distinct Dehalococcoides organisms. Subsequent transfers, along with quantitative PCR monitoring, yielded isolate GT, possessing only vcrA. These findings suggest that commonly used qualitative 16S rRNA gene-based procedures are insufficient to verify purity of Dehalococcoides cultures. Phylogenetic analysis revealed that strain GT is affiliated with the Pinellas group of the Dehalococcoides cluster and shares 100% 16S rRNA gene sequence identity with two other Dehalococcoides isolates, strain FL2 and strain CBDB1. The new isolate is distinct, as it respires the priority pollutants TCE, cis-1,2-dichloroethene (cis-DCE), 1,1-dichloroethene (1,1-DCE), and vinyl chloride (VC), thereby producing innocuous ethene and inorganic chloride. Strain GT dechlorinated TCE, cis-DCE, 1,1-DCE, and VC to ethene at rates up to 40, 41, 62, and 127 micromol liter-1 day-1, respectively, but failed to dechlorinate PCE. Hydrogen was the required electron donor, which was depleted to a consumption threshold concentration of 0.76+/-0.13 nM with VC as the electron acceptor. In contrast to the known TCE dechlorinating isolates, strain GT dechlorinated TCE to ethene with very little formation of chlorinated intermediates, suggesting that this type of organism avoids the commonly observed accumulation of cis-DCE and VC during TCE-to-ethene dechlorination.
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PMID:Quantitative PCR confirms purity of strain GT, a novel trichloroethene-to-ethene-respiring Dehalococcoides isolate. 1651 46

Reductive dehalogenation of vinyl chloride (VC) was studied in an anaerobic mixed bacterial culture. In growth experiments, ethene formation from VC increased exponentially at a rate of about 0.019 h(sup-1). Reductive VC dehalogenation was measured in vitro by using cell extracts of the mixed culture. The apparent K(infm) for VC was determined to be about 76 (mu)M; the V(infmax) was about 28 nmol (middot) min(sup-1) (middot) mg of protein(sup-1). The VC-dehalogenating activity was membrane associated. Propyl iodide had an inhibitory effect on the VC-dehalogenating activity in the in vitro assay. However, this inhibition could not be reversed by illumination. Cell extracts also catalyzed the reductive dehalogenation of cis-1,2-dichloroethene (cis-DCE) and, at a lower rate, of trichloroethene (TCE). Tetrachloroethene (PCE) was not transformed. The results indicate that the reductive dehalogenation of VC and cis-DCE described here is different from previously reported reductive dehalogenation of PCE and TCE.
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PMID:In vitro studies on reductive vinyl chloride dehalogenation by an anaerobic mixed culture. 1653 22

This study investigated the biotransformation pathways of 1,1,2,2-tetrachloroethane (1,1,2,2-TeCA) in the presence of chloroethenes (i.e. tetrachloroethene, PCE; trichloroethene, TCE) in anaerobic microcosms constructed with subsurface soil and groundwater from a contaminated site. When amended with yeast extract, lactate, butyrate, or H2 and acetate, 1,1,2,2-TeCA was initially dechlorinated via both hydrogenolysis to 1,1,2-trichloroethane (1,1,2-TCA) (major pathway) and dichloroelimination to dichloroethenes (DCEs) (minor pathway), with both reactions occurring under sulfidogenic conditions. In the presence of only H2, the hydrogenolysis of 1,1,2,2-TeCA to 1,1,2-TCA apparently required the presence of acetate to occur. Once formed, 1,1,2-TCA was degraded predominantly via dichloroelimination to vinyl chloride (VC). Ultimately, chloroethanes were converted to chloroethenes (mainly VC and DCEs) which persisted in the microcosms for very long periods along with PCE and TCE originally present in the groundwater. Hydrogenolysis of chloroethenes occurred only after highly reducing methanogenic conditions were established. However, substantial conversion to ethene (ETH) was observed only in microcosms amended with yeast extract (200 mg/l), suggesting that groundwater lacked some nutritional factors which were likely provided to dechlorinating microorganisms by this complex organic substrate. Bioaugmentation with an H2-utilizing PCE-dechlorinating Dehalococcoides spp. -containing culture resulted in the conversion of 1,1,2,2-TeCA, PCE and TCE to ETH and VC. No chloroethanes accumulated during degradation suggesting that 1,1,2,2-TeCA was degraded through initial dichloroelimination into DCEs and then typical hydrogenolysis into ETH and VC.
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PMID:Anaerobic bioremediation of groundwater containing a mixture of 1,1,2,2-tetrachloroethane and chloroethenes. 1671 99

Chitin, corncobs, and a mixture of chitin and corncobs were tested as potential electron donor sources for stimulating the reductive dechlorination of tetrachloroethene (PCE). Semi-batch, sand-packed columns were used to evaluate the donors with aerobic and anaerobic groundwaters containing varying degrees of alkalinity. In all experiments, acetate and butyrate were the dominant fatty acids produced, although propionate, valerate, formate, and succinate were also detected. From a multivariable regression analysis on the data, the presence of chitin, limestone, and dechlorinating culture inoculum were determined to be the most positive predictors of dechlorination activity. Chitin fermentation products supported the degradation of PCE to trichloroethene (TCE), cis-1,2-dichloroethene (DCE), and vinyl chloride (VC), even in columns containing PCE DNAPL, whereas dechlorination activity was not observed in any of the columns containing corncobs alone. The longevity and efficiency of chitin as an electron donor source demonstrates its potential usefulness for passive, in situ field applications.
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PMID:Chitin and corncobs as electron donor sources for the reductive dechlorination of tetrachloroethene. 1672 76


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