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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)

Aerobic enrichment cultures from contaminated groundwaters dechlorinated trichloroethylene (TCE) (14.6 mg/liter; 111 mumol/liter) and tetrachloroethylene (PCE) (16.2 mg/liter; 98 mumol/liter) reductively within 4 days after the transition from aerobic to anaerobic conditions. The transformation products were equimolar amounts of cis-1,2-dichloroethylene and traces of 1,1-dichloroethylene. No other chlorinated product and no methane were detected. The change was accompanied by the release of sulfide, which caused a decrease in the redox potential from 0 to -150 mV. In sterile control experiments, sulfide led to the abiotic formation of traces of 1,1-dichloroethylene without cis-1,2-dichloroethylene production. The reductive dechlorination of PCE via TCE depended on these specific transition conditions after consumption of the electron acceptor oxygen or nitrate. Repeated feeding of TCE or PCE to cultures after the change to anaerobic conditions yielded no further dechlorination. Only aerobic subcultures with an air/liquid ratio of 1:4 maintained dechlorination activities; anaerobic subcultures showed no transformation. Bacteria from noncontaminated sites showed no reduction under the same conditions.
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PMID:Reductive dechlorination of Tri- and tetrachloroethylenes depends on transition from aerobic to anaerobic conditions. 189 93

Cell-free extracts of Clostridium bifermentans DPH-1 catalyzed tetrachloroethylene (PCE) dechlorination. PCE degradation was stimulated by addition of a variety of electron donors. Ethanol (0.61 mM) was the most effective electron donor for PCE dechlorination. Maximum activity was recorded at 30 degrees C and pH 7.5. Addition of NADH as a cofactor stimulated enzymatic activity but the activity was not stimulated by addition of metal ions. When the cell-free enzyme extract was incubated in the presence of titanium citrate as a reducing agent, the dehalogenase was rapidly inactivated by propyl iodide (0.5 mM). The activity of propyliodide-reacted enzyme was restored by illumination with a 250 W lamp. The dehalogenase activity was also inhibited by cyanide. The substrate spectrum of activity included trichloroethylene (TCE), cis-1,2-dichloroethylene (cDCE), trans-dichloroethylene, 1,1-dichloroethylene, 1,2-dichloroethane, and 1,1,2-trichloroethane. The highest rate of degradation of the chlorinated aliphatic compounds was achieved with PCE, and PCE was principally degraded via TCE to cDCE. Results indicate that the dehalogenase could play a vital role in the breakdown of PCE as well as a variety of other chlorinated aliphatic compounds.
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PMID:In vitro dehalogenation of tetrachloroethylene (PCE) by cell-free extracts of Clostridium bifermentans DPH-1. 1133 32

An enzyme mediating the reductive dechlorination of tetrachloroethylene (PCE) from cell-free extracts of Clostridium bifermentans DPH-1 was purified, cloned, and sequenced. The enzyme catalyzed the reductive dechlorination of PCE to cis-1,2-dichloroethylene via trichloroethylene, at a Vmax and Km of 73 nmol/mg protein and 12 microM, respectively. Maximal activity was recorded at 35 degrees C and pH 7.5. Enzymatic activity was independent of metal ions but was oxygen sensitive. A mixture of propyl iodide and titanium citrate caused a light-reversible inhibition of enzymatic activity suggesting the involvement of a corrinoid cofactor. The molecular mass of the native enzyme was estimated to be approximately 70 kDa. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and matrix-assisted laser desorption ionization-time of flight/mass spectrometry (MALDI-TOF/MS) revealed molecular masses of approximately 35 kDa and 35.7 kDa, respectively. A broad spectrum of chlorinated aliphatic compounds (PCE, trichloroethylene, cis-1,2-dichloroethylene, trans-1,2-dichloroethylene, 1,1-dichloroethylene, 1,2-dichloropropane, and 1,1,2-trichloroethane) was degraded. With degenerate primers designed from the N-terminal sequence (27 amino acid residues), a partial sequence (81 bp) of the encoding gene was amplified by polymerase chain reaction (PCR) and sequenced. Southern analysis of C. bifermentans genomic DNA using the PCR product as a probe revealed restriction fragment bands. A 5.0 kb ClaI fragment, harboring the relevant gene (designated pceC) was cloned (pDEHAL5) and the complete nucleotide sequence of pceC was determined. The gene showed homology mainly with microbial membrane proteins and no homology with any known dehalogenase, suggesting a distinct PCE dehalogenase.
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PMID:Purification, cloning, and sequencing of an enzyme mediating the reductive dechlorination of tetrachloroethylene (PCE) from Clostridium bifermentans DPH-1. 1140 Jul 36

A recombinant strain of Escherichia coli (JM109/pBZ1260) expressing constitutively toluene-o-xylene monooxygenase (ToMO) of Pseudomonas stutzeri OX1 degraded binary mixtures (100 microM each) of tetrachloroethylene (PCE) with either trichloroethylene (TCE), 1,1-dichloroethylene (1,1-DCE), cis-dichloroethylene (cis-DCE), trans-1,2-dichloroethylene (trans-DCE), or vinyl chloride (VC). PCE degradation was 8-20% for these binary mixtures, while TCE and trans-DCE with PCE were degraded at 19%, 1,1-DCE at 37%, cis-DCE at 97%, and VC at 27%. The host P. stutzeri OXI was also found to degrade binary mixtures of PCE/TCE, PCE/cis-DCE, and PCE/VC when induced with toluene. Degradation of quaternary mixtures of PCE/TCE/trans-DCE/VC and PCE/TCE/cis-DCE/VC by JM109/pBZ1260 were also investigated as well as mixtures of PCE/TCE/trans-DCE/1,1-DCE/cis-DCE/VC; when all the chlorinated compounds were present, the best degradation occurred with 24-51% removal of each. For these degradation reactions, 39-85% of the stoichiometric chloride expected from complete degradation of the chlorinated ethenes was detected. The time course of PCE/TCE/1,1-DCE degradation was also measured for a mixture of 8, 17, and 6 microM, respectively; initial degradation rates were 0.015, 0.023. and 0.029 nmol/min x mg protein, respectively. This indicates that for the first time an aerobic enzyme can degrade mixtures of all chlorinated ethenes, including the once--so it was believed-completely recalcitrant PCE.
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PMID:Aerobic degradation of mixtures of tetrachloroethylene, trichloroethylene, dichloroethylenes, and vinyl chloride by toluene-o-xylene monooxygenase of Pseudomonas stutzeri OX1. 1149 42

Permanganate oxidation of chlorinated ethylenes is an attractive technique to effect remediation of these important groundwater contaminants. Stable carbon isotope fractionation associated with permanganate oxidation of trichloroethylene (TCE), tetrachloroethylene (PCE), and cis-1,2-dichloroethylene (cDCE) has been measured, to study the possibility of applying stable carbon isotope analysis as a technique to assess the efficacy of remediation implemented by permanganate oxidation. Average carbon isotope fractionation factors of alphaTCE = 0.9786, alphaPCE = 0.9830, and alphacDCE = 0.9789 were obtained, although the fractionation factor for PCE may be interpreted to change from a value of 0.9779-0.9871 during the course of the reaction. The fractionation factors for all three compounds are quite similar, in contrast to the variation of fractionation factors vs degree of chlorination observed for other degradative processes, such as microbial dechlorination. This may be due to a common rate-determining step for permanganate oxidation of all three compounds studied. The large fractionation factors and the relative lack of dependence of the fractionation factors upon other environmental factors (e.g. oxidation rate, presence of multiple contaminants, incomplete oxidation, presence of chloride in solution) indicate that monitoring delta13C values of chlorinated ethylenes during oxidation with permanganate may be a sensitive, and potentially quantitative, technique to investigate the extent of degradation.
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PMID:Carbon isotope fractionation during permanganate oxidation of chlorinated ethylenes (cDCE, TCE, PCE). 1218 52

A laboratory sequential anaerobic-aerobic bioreactor system, which consisted of an anaerobic fixed film reactor and two aerobic chemostats, was set up to degrade tetrachloroethylene (PCE) without accumulating highly toxic degradation intermediates. A soil enrichment culture, which could reductively dechlorinate 900 microM (ca. 150 mg/L) of PCE stoichiometrically into cis-1,2-dichloroethylene (cis-DCE), was attached to ceramic media in the anaerobic fixed film reactor. A phenol degrading strain, Alcaligenes sp. R5, which can efficiently degrade cis-DCE by co-metabolic oxidation, was used as inoculum for the aerobic chemostats consisted of a transformation reactor and a growth reactor. The anaerobic fixed film bioreactor showed more than 99% of PCE transformation into cis-DCE in the range of influent PCE concentration from 5 microM to 35 microM at hydraulic retention time of 48 h. On the other hand, efficient degradation of the resultant cis-DCE by strain R5 in the following aerobic system could not be achieved due to oxygen limitation. However, 54% of the maximum cis-DCE degradation was obtained when 10 mumol of hydrogen peroxide (H2O2) was supplemented to the transformation reactor as an additional oxygen source. Further studies are needed to achieve more efficient co-metabolic degradation of cis-DCE in the aerobic reactor.
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PMID:A reactor system combining reductive dechlorination with co-metabolic oxidation for complete degradation of tetrachloroentylene. 1249 16

The chemotactic responses of Pseudomonas putida F1, Burkholderia cepacia G4, and Pseudomonas stutzeri OX1 were investigated toward toluene, trichloroethylene (TCE), tetrachloroethylene (PCE), cis-1,2-dichloroethylene (cis-DCE), trans-1,2-dichloroethylene (trans-DCE), 1,1-dichloroethylene (1,1-DCE), and vinyl chloride (VC). P. stutzeri OX1 and P. putida F1 were chemotactic toward toluene, PCE, TCE, all DCEs, and VC. B. cepacia G4 was chemotactic toward toluene, PCE, TCE, cis-DCE, 1,1-DCE, and VC. Chemotaxis of P. stutzeri OX1 grown on o-xylene vapors was much stronger than when grown on o-cresol vapors toward some chlorinated ethenes. Expression of toluene-o-xylene monooxygenase (ToMO) from touABCDEF appears to be required for positive chemotaxis attraction, and the attraction is stronger with the touR (ToMO regulatory) gene.
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PMID:Chemotaxis of Pseudomonas stutzeri OX1 and Burkholderia cepacia G4 toward chlorinated ethenes. 1529 Jan 36

A tetrachloroethylene (PCE)-degrading gram-positive, endospore forming, anaerobic bacterium, strain DPH-1, was isolated from a contaminated site. The organism was identified as Clostridium bifermentans by 16S rRNA gene sequence analysis and based on its physiological characteristics. Strain DPH-1 could dechlorinate high concentrations of PCE (0.9 mM), via trichloroethylene (TCE) to cis-1,2-dichloroethylene (cDCE) at a rate of 0.43 micromol/h.mg protein, as well as a number of other halogenated aliphatic compounds.
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PMID:Isolation and characterization of a tetrachloroethylene dechlorinating bacterium, Clostridium bifermentans DPH-1. 1623 83

A laboratory test was conducted to examine the combined effect of bioaugmentation of an anaerobic bacterial Desulfitobacterium sp. strain Y-51 and addition of zero-valent iron (Fe0) on the reductive dechlorination of tetrachloroethylene (PCE) in a non-sterile soil slurry. Introduction of a strain Y-51 culture in soil (3 mg vss (volatile suspended solids)/kg soil) containing PCE (at 60 micromol/kg soil) led to complete conversion of PCE to cis-1,2-dichloroethylene (cis-DCE) within 40 d. Treatments of the same soil slurry with Fe0 (0.1-1.0%) resulted in extended PCE dechlorination to ethylene (ETH) and ethane (ETA). The combined use of a strain Y-51 culture and Fe0 showed effective dechlorination of PCE than did the individual use. The cis-DCE produced from biological PCE dechlorination by strain Y-51 was totally converted to non-chlorinated end products by the following chemical reduction by Fe0. Furthermore, anaerobic corrosion of Fe0 was found to stimulate the biological reductive dechlorination of PCE by keeping proper levels of pH and oxidation-reduction potential (ORP) and by producing cathodic hydrogen, which might be used as an electron donor for respiratory PCE dechlorination. These findings suggest that the combined use of bacterial strain Y-51 and Fe0 is effective for practical treatment of PCE and other chlorinated ethylenes in contaminated sites.
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PMID:Efficient dechlorination of tetrachloroethylene in soil slurry by combined use of an anaerobic Desulfitobacterium sp. strain Y-51 and zero-valent iron. 1623 27

A laboratory test was conducted to examine the combined effect of an anaerobic Clostridium bifermentans DPH-1 and addition of zero-valent iron (Fe0) on the reductive dechlorination of tetrachloroethylene (PCE). In addition, the dechlorination of cis-1,2-dichloroethylene (cDCE) produced from PCE was examined using Fe0. The cDCE produced was completely dechlorinated to non-toxic end products, mostly, ethylene by a subsequent chemical reductive process. Production of ethylene was dramatically increased with increase of initial cDCE concentration in the range of 10.3 microM to 928 microM (1.0-90 mg l(-1)) and the velocity constant was calculated to be 0.38 day(-1). On the other hand, the combined use of strain DPH-1 and Fe0 showed the most significant effect on the initial PCE dechlorination, but cohesion of Fe0 was found to inhibit the dechlorination rate of PCE. It is thought that phosphoric acid iron contained in a medium forms film on the surface of iron particle, so oxidation of iron is inhibited.
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PMID:Complete dechlorination of tetrachloroethylene by use of an anaerobic Clostridium bifermentans DPH-1 and zero-valent iron. 1861 43


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