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1.
G D Griffith J R Cole J F Quensen J M Tiedje 《Applied and environmental microbiology》1992,58(1):409-411
Desulfomonile tiedjei DCB-1 is a strict anaerobe capable of reductively dechlorinating meta-chlorobenzoates. To probe the mechanism of this aryl dechlorination, we incubated cell suspensions of D. tiedjei in D2O and with 2,5-dichlorobenzoate. The deuterium was incorporated into the dechlorination product exclusively at the position of dehalogenation, as shown by gas chromatography-mass spectrometry and proton magnetic resonance analyses. These results favor a model for dechlorination that should not allow proton exchange at other positions, as would be the case if partial ring reduction occurred. 相似文献
2.
Influence of sulfur oxyanions on reductive dehalogenation activities in Desulfomonile tiedjei.
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The inhibition of aryl reductive dehalogenation reactions by sulfur oxyanions has been demonstrated in environmental samples, dehalogenating enrichments, and the sulfate-reducing bacterium Desulfomonile tiedjei; however, this phenomenon is not well understood. We examined the effects of sulfate, sulfite, and thiosulfate on reductive dehalogenation in the model microorganism D. tiedjei and found separate mechanisms of inhibition due to these oxyanions under growth versus nongrowth conditions. Dehalogenation activity was greatly reduced in extracts of cells grown in the presence of both 3-chlorobenzoate, the substrate or inducer for the aryl dehalogenation activity, and either sulfate, sulfite, or thiosulfate, indicating that sulfur oxyanions repress the requisite enzymes. In extracts of fully induced cells, thiosulfate and sulfite, but not sulfate, were potent inhibitors of aryl dehalogenation activity even in membrane fractions lacking the cytoplasmically located sulfur oxyanion reductase. These results suggest that under growth conditions, sulfur oxyanions serve as preferred electron acceptors and negatively influence dehalogenation activity in D. tiedjei by regulating the amount of active aryl dehalogenase in cells. Additionally, in vitro inhibition by sulfur oxyanions is due to the interaction of the reactive species with enzymes involved in dehalogenation and need not involve competition between two respiratory processes for reducing equivalents. Sulfur oxyanions also inhibited tetrachloroethylene dehalogenation by the same mechanisms, further indicating that chloroethylenes are fortuitously dehalogenated by the aryl dehalogenase. The commonly observed inhibition of reductive dehalogenation reactions under sulfate-reducing conditions may be due to similar regulation mechanisms in other dehalogenating microorganisms that contain multiple respiratory activities. 相似文献
3.
Reductive dehalogenation of chlorophenols has been reported in undefined anaerobic cultures but never before in an anaerobic pure culture. We found that the sulfate-reducing bacterium Desulfomonile tiedjei DCB-1 reductively dehalogenates pentachlorophenol (PCP) and other chlorophenols. The maximum rate of PCP dechlorination observed was 54 mu mol of Cl- h-1 g of protein-1. 3-Chlorobenzoate appeared to serve as a required inducer for PCP dehalogenation; however, neither PCP nor 3-chlorophenol induced dehalogenation. Dehalogenation was catalyzed by living cells, and formate served as a required electron donor. D. tiedjei dehalogenated meta-chlorine substituents of chlorophenols (i.e., PCP was degraded to 2,4,6-trichlorophenol). Generally, more highly chlorinated phenol congeners were more readily dechlorinated, and 3-chlorophenol was not dehalogenated. Growing cultures dehalogenated PCP, but greater than 10 microM PCP (approximately 1.7 mmol g of protein-1) reversibly inhibited growth. 相似文献
4.
Reductive dehalogenation of chlorophenols has been reported in undefined anaerobic cultures but never before in an anaerobic pure culture. We found that the sulfate-reducing bacterium Desulfomonile tiedjei DCB-1 reductively dehalogenates pentachlorophenol (PCP) and other chlorophenols. The maximum rate of PCP dechlorination observed was 54 mu mol of Cl- h-1 g of protein-1. 3-Chlorobenzoate appeared to serve as a required inducer for PCP dehalogenation; however, neither PCP nor 3-chlorophenol induced dehalogenation. Dehalogenation was catalyzed by living cells, and formate served as a required electron donor. D. tiedjei dehalogenated meta-chlorine substituents of chlorophenols (i.e., PCP was degraded to 2,4,6-trichlorophenol). Generally, more highly chlorinated phenol congeners were more readily dechlorinated, and 3-chlorophenol was not dehalogenated. Growing cultures dehalogenated PCP, but greater than 10 microM PCP (approximately 1.7 mmol g of protein-1) reversibly inhibited growth. 相似文献
5.
Relationship between hydrogen consumption, dehalogenation, and the reduction of sulfur oxyanions by Desulfomonile tiedjei 总被引:6,自引:0,他引:6
Resting-cell suspensions of Desulfomonile tiedjei consumed H2 with 3-chloro-, 3-bromo-, and 3-iodobenzoate as electron acceptors with rates of 0.50, 0.44, and 0.04 mumol h-1 mg-1, respectively. However, benzoate and 3-fluorobenzoate were not metabolized by this bacterium. In addition, H2 uptake was at least fourfold faster when sulfate, sulfite, or thiosulfate was available as the electron acceptor instead of a haloaromatic substrate. When sulfite and 3-chlorobenzoate were both available for this purpose, the rate of H2 uptake by D. tiedjei was intermediate between that obtained with either electron acceptor alone. Hydrogen concentrations were reduced to comparably low levels when either 3-chlorobenzoate, sulfate, or sulfite was available as an electron acceptor, but significantly less H2 depletion was evident with benzoate or nitrate. Rates of 3-chlorobenzoate dechlorination increased from an endogenous rate of 14.5 to 17.1, 74.0, 81.1, and 82.3 nmol h-1 mg-1 with acetate, pyruvate, H2, and formate, respectively, as the electron donors. Sulfite and thiosulfate inhibited dehalogenation, but sulfate and NaCl had no effect. Dehalogenation and H2 metabolism were also inhibited by acetylene, molybdate, selenate, and metronidazole. Sulfite reduction and dehalogenation were inhibited by the same respiratory inhibitors. These results suggest that the reduction of sulfite and dehalogenation may share part of the same electron transport chain. The kinetics of H2 consumption and the direct inhibition of dehalogenation by sulfite and thiosulfate in D. tiedjei cells clearly indicate that the reduction of sulfur oxyanions is favored over aryl dehalogenation for the removal of reducing equivalents under anaerobic conditions.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
6.
Desulfomonile tiedjei (strain DCB-1) was previously shown to conserve energy for growth from reductive dechlorination of 3-chlorobenzoate coupled to formate oxidation. We tested the hypothesis that a chemiosmotic mechanism couples reductive dechlorination and ATP synthesis in D. tiedjei. Dechlorination resulted in an increase in the ATP pool of cells. Uncouplers and ionophores decreased both the dechlorination rate and the ATP pool. However, at low concentrations the inhibitors had relatively greater effects on the ATP pool, and in some cases, even appeared to stimulate dechlorination. Those agents could not completely inhibit ATP synthesis while allowing dechlorination activity. The proton-driven ATPase inhibitor, N,N-dicyclohexylcarbodiimide (DCCD), had similar effects. An imposed pH gradient also resulted in an increase in the ATP pool of cells, and this increase was partially inhibited by DCCD. Addition of 3-chlorobenzoate to cell suspensions caused proton translocation by the cells. Proton translocation was stimulated by the permeant thiocyanate anion and inhibited by uncouplers. A maximum H+/3-chlorobenzoate ratio of greater than two was observed. These findings suggest that dechlorination supports formation of a proton-motive force which in turn supports ATP synthesis via a proton-driven ATPase.Abbreviations 3CB
3-chlorobenzoate
- CCCP
m-chlorophenyl-hydrazone
- DCCD
N,N-dicyclohexylcarbodiimide
- DNP
2,4-dinitrophenol
- P
proton-motive force
- PCP
pentachlorophenol 相似文献
7.
Anaerobic Aryl Reductive Dehalogenation of Halobenzoates by Cell Extracts of "Desulfomonile tiedjei"
We studied the transformation of halogenated benzoates by cell extracts of a dehalogenating anaerobe, "Desulfomonile tiedjei." We found that cell extracts possessed aryl reductive dehalogenation activity. The activity was heat labile and dependent on the addition of reduced methyl viologen, but not on that of reduced NAD, NADP, flavin mononucleotide, flavin adenine dinucleotide, desulfoviridin, cytochrome c(3), or benzyl viologen. Dehalogenation activity in extracts was stimulated by formate, CO, or H(2), but not by pyruvate plus coenzyme A or by dithionite. The pH and temperature optima for aryl dehalogenation were 8.2 and 35 degrees C, respectively. The rate of dehalogenation was proportional to the amount of protein in the assay mixture. The substrate specificity of aryl dehalogenation activity for various aromatic compounds in "D. tiedjei" cell extracts was identical to that of whole cells, except differences were observed in the relative rates of halobenzoate transformation. Dehalogenation was 10-fold greater in "D. tiedjei" extracts prepared from cells cultured in the presence of 3-chlorobenzoate, suggesting that the activity was inducible. Aryl reductive dehalogenation in extracts was inhibited by sulfite, sulfide, and thiosulfate, but not sulfate. Experiments with combinations of substrates suggested that cell extracts dehalogenated 3-iodobenzoate more readily than either 3,5-dichlorobenzoate or 3-chlorobenzoate. Dehalogenation activity was found to be membrane associated. This is the first report characterizing aryl dehalogenation activity in cell extracts of an obligate anaerobe. 相似文献
8.
Saïd El Fantroussi Jacques Mahillon Henry Naveau Spiros N. Agathos 《Biodegradation》1997,8(2):125-133
The aim of this work was to test the feasibility ofintroducing an anaerobic microbial reductivedechlorination activity into non sterile soil slurrymicrocosms by inoculation with the pure anaerobicbacterial strain Desulfomonile tiedjei, which iscapable of dechlorinating 3-chlorobenzoate tobenzoate. To show that the bacterium was establishedin the microcosms we followed the expression of thereductive dechlorination activity and a molecularprobe based on PCR amplification of the 16S rDNA genewas developed. However, the success of PCRamplification of the 16S rDNA gene depends on the DNAextraction and purification methodologies applied, asshown through the use of several protocols. In thisstudy we report a DNA extraction and purificationmethod which generates sufficient and very clean DNAsuitable for PCR amplification of the D. tiedjei16S rDNA gene. The threshold of detection was about5.103 bacteria per gram of soil slurry.Introduction of D. tiedjei in soil slurrymicrocosms proved successful since 3-chlorobenzoatedechlorination activity was established with thisbacterium in microcosms normally devoid of thisdechlorination capacity. Indeed, the addition of D. tiedjei to microcosms supplemented with acetateplus formate as cosubstrate, at their respectiveconcentrations of 5 and 6 mM, led to a totalbiotransformation of 2.5 mM of 3-chlorobenzoate within12 days. After complete 3-chlorobenzoatedechlorination, the 16S rDNA gene of this bacteriumwas specifically detected only in the inoculatedmicrocosms as shown by PCR amplification followed byrestriction mapping confirmation. 相似文献
9.
Characterization of Chloroethylene Dehalogenation by Cell Extracts of Desulfomonile tiedjei and Its Relationship to Chlorobenzoate Dehalogenation
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We characterized the reductive dehalogenation of tetrachloroethylene in cell extracts of Desulfomonile tiedjei and compared it with this organism's 3-chlorobenzoate dehalogenation activity. Tetrachloroethylene was sequentially dehalogenated to trichloro- and dichloroethylene; there was no evidence for dichloroethylene dehalogenation. Like the previously characterized 3-chlorobenzoate dehalogenation activity, tetrachloroethylene dehalogenation was heat sensitive, not oxygen labile, and increased in proportion to the amount of protein in assay mixtures. In addition, both dehalogenation activities were dependent on hydrogen or formate as an electron donor and had an absolute requirement for either methyl viologen or triquat as an electron carrier in vitro. Both activities appear to be catalyzed by integral membrane proteins with similar solubilization characteristics. Dehalogenation of tetrachloroethylene was inhibited by 3-chlorobenzoate but not by the structural isomers 2- and 4-chlorobenzoate. The last two compounds are not substrates for D. tiedjei. These findings lead us to suggest that the dehalogenation of tetrachloroethylene in D. tiedjei is catalyzed by a dehalogenase previously thought to be specific for meta-halobenzoates. 相似文献
10.
The sulfate-reducing bacterium, Desulfomonile tiedjei DCB-1, conserves energy for growth from reductive dechlorination of 3-chlorobenzoate via halorespiration. To understand this respiratory process better, we examined electron carriers from different cellular compartments of D. tiedjei. A 50-kDa cytochrome from the membrane fraction was found to be co-induced with dechlorination activity. This inducible cytochrome was extracted from the membrane fractions by Tris-HCl buffer containing ammonium sulfate at 35% saturation and was purified to electrophoretic homogeneity by phenyl superose, Mono Q, and hydroxyapatite chromatography. The purified cytochrome had a high-spin absorption spectrum. In a pH titration experiment, the absorption spectrum of the inducible cytochrome shifted to low spin at pH 13.2. The midpoint potential of the inducible cytochrome at pH 7.0 was –342 mV. The NH2-terminal amino acid sequence of the inducible cytochrome was determined and was used to obtain inverse PCR products containing the sequence of the gene encoding the inducible cytochrome. The ORF was 1398 bp and coded for a protein of 52.6 kDa. Two c-type heme-binding domains were identified in the COOH-terminal half of the protein. A putative signal peptide of 26 residues was found at the NH2-terminal end. The protein sequence was not found to have substantial sequence similarity to any other sequence in GenBank. We conclude that this is a c-type cytochrome substantially different from previously characterized c-type cytochromes. Received: 30 May 1997 / Accepted: 29 July 1997 相似文献
11.
Competition for molecular hydrogen exists amonghydrogen-utilizing microorganismsin anoxic environments, and evidence suggeststhat lower hydrogen concentrations areobserved with more energetically favorableelectron-accepting processes. The transferof electrons to organochlorines via reductivedehalogenation reactions plays an importantrole in hydrogen dynamics in impacted systems. Westudied the flux of aqueous hydrogenconcentrations in methanogenic sediment microcosmsprior to and during reductivedehalogenation of a variety of substituted chlorophenols(CP) and tetrachloroethene(perchloroethylene, PCE). Mean hydrogen concentrationsduring reductive dehalogenationof 2,4-CP, 2,3,4-CP, and PCP were 3.6 nM, 4.1 nM,and 0.34 nM, respectively. Sedimentmicrocosms that were not dosed with chlorophenolsyet were actively methanogenicmaintained a significantly higher mean hydrogenconcentration of 9.8 nM. Duringactive PCE dehalogenation, sediment microcosmsmaintained a mean hydrogenconcentration of 0.82 nM. These data indicate thatduring limiting hydrogen production,the threshold ecosystem hydrogen concentration iscontrolled by microbial populationsthat couple hydrogen oxidation to thermodynamicallyfavorable electron acceptingreactions, including reductive dehalogenationof chloroaromatic compounds. Wealso present revised estimates for the Gibbsfree energy available from the reductivedehalogenation of a variety of substitutedchlorophenols based on recently publishedvalues of vapor pressure, solubility, and pKafor these compounds. 相似文献
12.
D.B. Ringelberg G.T. Townsend K.A. DeWeerd J.M. Suflita D.C. White 《FEMS microbiology ecology》1994,14(1):9-18
Abstract Desulfomonile tiedjei is a Gram-negative sulfate-reducing bacterium capable of catalyzing aryl reductive dehalogenation reactions. Since many toxic and persistent contaminants in the subsurface are halogenated aromatic compounds, the detection and enumeration of dehalogenating microorganisms in the environment may be a useful tool for planning and evaluating bioremediation efforts. In this study, we show that D. tiedjei contains unique lipopolysaccharide branched 3-hydroxy fatty acids, unknown as yet in other bacteria, and that it is possible to detect the bacterium in inoculated aquifer sediments based on these signature lipid biomarkers. The detection of D. tiedjei and other dehalogenating microorganisms possessing similar cellular properties in environmental matrices may be possible by this technique. Additionally, the effect of such inoculation on dehalogenation activity is examined. 相似文献
13.
Isolation and characterization of a novel bacterium growing via reductive dehalogenation of 2-chlorophenol. 总被引:4,自引:8,他引:4
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A bacterium capable of anaerobic growth via reductive dehalogenation of 2-chlorophenol was isolated from a culture enriched from sediment taken from a small stream near Lansing, Mich. The organism, designated strain 2CP-1, is a gram-negative rod ca. 3 by 0.5 micron in size and is a catalase-negative, oxidase-negative, facultative anaerobe that forms small red colonies in anaerobic media. The organism grew in reduced anaerobic mineral medium supplemented with 2-chlorophenol, acetate, and vitamins, producing phenol as a product. It did not grow when either 2-chlorophenol or acetate was omitted. The growth yield was about 3 g of protein per mol of 2-chlorophenol dechlorinated, and the doubling time was 3.7 days. Only the ortho position was dehalogenated, and additional chlorines at other positions decreased or blocked ortho dechlorination. The organism also grew with fumarate as its electron acceptor. Dechlorination activity is inducible, since cultures grown in fumarate containing medium with 2-chlorophenol rapidly dechlorinated additional 2-chlorophenol, while cultures grown in the same medium without 2-chlorophenol did not. Analysis of the organism's 16S rRNA sequence revealed that it is a member of the delta proteobacteria, more closely related to the myxobacteria than to the sulfidogenic bacteria. 相似文献
14.
Tetrachlorohydroquinone dehalogenase catalyzes two successive reductive dehalogenation reactions in the pathway for degradation of pentachlorophenol in the soil bacterium Sphingobium chlorophenolicum. We have used pre-steady-state kinetic methods to probe both the mechanism and the rates of elementary steps in the initial stages of the reductive dehalogenation reaction. Binding of trichlorohydroquinone (TriCHQ) to the active site is followed by rapid deprotonation to form TriCHQ-2 and subsequent formation of 3,5,6-trichloro-4-hydroxycyclohexa-2,4-dienone (TriCHQ*). Further conversion of TriCHQ* to 2,6-dichlorohydroquinone (DCHQ) proceeds only in the presence of glutathione. Conversion of TriCHQ to DCHQ during the first turnover is quite rapid, occurring at about 25 s-1 when the enzyme is saturated with TriCHQ and glutathione. The rate of subsequent turnovers is limited by the rate of the thiol-disulfide exchange reaction required to regenerate the free enzyme after turnover, a reaction that is intrinsically less difficult, but is hampered by premature binding of the aromatic substrate to the active site before the catalytic cycle is completed. 相似文献
15.
Purification and characterization of a novel 3-chlorobenzoate-reductive dehalogenase from the cytoplasmic membrane of Desulfomonile tiedjei DCB-1. 总被引:2,自引:2,他引:2
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Although reductive dehalogenation by anaerobic microorganisms offers great potential for the degradation of halocarbons, little is known about the biochemical mechanisms involved. It has previously been demonstrated that the dehalogenase activity involved in 3-chlorobenzoate dehalogenation by Desulfomonile tiedjei DCB-1 is present in the membrane fraction of the cell extracts. We report herein the purification of a 3-chlorobenzoate-reductive dehalogenase from the cytoplasmic membrane of D. tiedjei DCB-1. The dehalogenase activity was monitored by the conversion of 3-chlorobenzoate to benzoate with reduced methyl viologen as a reducing agent. The membrane fraction of the cell extracts was obtained by ultracentrifugation, and the membrane proteins were solubilized with either the detergent CHAPS (3-[(3-cholamidopropyl)-dimethyl-ammonio]-1-propanesulfonate) or Triton X-100 in the presence of glycerol. The solubilized dehalogenase was purified by ammonium sulfate fractionation and a combination of anion exchange, hydroxyapatite, and hydrophobic interaction chromatographies. This procedure yielded about 7% of the total dehalogenase activity with a 120-fold increase in specific activity. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that the purified dehalogenase consisted of two subunits with molecular weights of 64,000 and 37,000. The enzyme converted 3-chlorobenzoate to benzoate at its highest specific activity in 10 mM potassium phosphate buffer (pH 7.2) at 38 degrees C. The enzyme was yellow and probably a heme protein. The enzyme had an adsorbance peak at 408 nm. The dithionite-reduced enzyme displayed absorbance peaks at 416, 522, and 550 nm. The dithionite-reduced enzyme was able to complex with carbon monoxide. The nature of the heme chromophore is currently unknown. 相似文献
16.
Specificity of reductive dehalogenation of substituted ortho-chlorophenols by Desulfitobacterium dehalogenans JW/IU-DC1. 总被引:1,自引:2,他引:1
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Resting cells of Desulfitobacterium dehalogenans JW/IU-DC1 growth with pyruvate and 3-chloro-4-hydroxyphenylacetate (3-Cl-4-OHPA) as the electron acceptor and inducer of dehalogenation reductively ortho-dehalogenate pentachlorophenol (PCP); tetrachlorophenols (TeCPs); the trichlorophenols 2,3,4-TCP, 2,3,6-TCP, and 2,4,6-TCP; the dichlorophenols 2,3-DCP, 2,4-DCP, and 2,6-DCP; 2,6-dichloro-4-R-phenols (2,6-DCl-4-RPs, where R is -H, -F, -Cl, -NO2, -CO2, or -COOCH3; 2-chloro-4-R-phenols (2-Cl-4-RPs, where R is -H, -F, -Cl, -Br, -NO2, -CO2-, -CH2CO2, or -COOCH3); and the bromophenols 2-BrP, 2,6-DBrP, and 2-Br-4ClP [corrected]. Monochlorophenols, the dichlorophenols 2,5-DCP, 3,4-DCP, and 3,5-DCP, the trichlorophenols 2,3,5-TCP, 2,4,5-TCP, and 3,4,5-TCP, and the fluorinated analog of 3-Cl-4-OHPA, 3-F-4-OHPA (2-F-4-CH2CO2- P), are not dehalogenated. A chlorine substituent in position 3 (meta), 4 (para), or 6 (second ortho) of the phenolic moiety facilitates ortho dehalogenation in position 2. Chlorine in the 5 (second meta) position has a negative effect on the dehalogenation rate or even prevents dechlorination in the 2 position. In general, 2,6-DCl-4-RPs are dechlorinated faster than the corresponding 2-Cl-4-RPs with the same substituent R in the 4 position. The highest dechlorination rate, however, was found for dechlorination of 2,3-DCP, with a maximal observed first-order rate constant of 19.4 h-1 g (dry weight) of biomass-1.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
17.
Characterization of the requirements and substrates for reductive dehalogenation by strain DCB-1 总被引:17,自引:0,他引:17
Summary An obligately anaerobic bacterium known as strain DCB-1 was grown under a variety of conditions to determine the requirements for dehalogenation as well as factors which stimulated or inhibited the process. Dechlorination was obligately anaerobic since introduction of O2 immediately inhibited the reaction. Sulfuroxy anions, which also serve as electron acceptors for DCB-1, inhibited dechlorination but NO3
– and fumarate did not. The optimum growth medium for dechlorination was 0.2% Na pyruvate and 20% rumen fluid in basal salts. Media with either pyruvate or rumen fluid alone did not support dechlorination. DCB-1 also consumed H2 but typical substrate concentrations of H2 (80 kPa) delayed dechlorination. Once the H2 concentration was reduced to <20 M (2.67 kPa), dechlorination resumed. Dehalogenation by DCB-1 was restricted to the meta substituted benzoates as halogens in other positions and chloroaromatic compounds with other functional groups were not dechlorinated. 相似文献
18.
Extrapolation of biodegradation results to groundwater aquifers: reductive dehalogenation of aromatic compounds. 总被引:2,自引:20,他引:2
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The reductive biodegradation of a variety of haloaromatic substrates was monitored in samples from two sites within a shallow anoxic aquifer and was compared with freshwater sediment and sewage sludge. The metabolic capacity existing in methane-producing aquifer material was very similar to that in sediment in that three of four chlorobenzoates, five of seven chlorophenols, and one of two chlorophenoxyacetate herbicides were reductively dehalogenated in both types of incubations. The 2,4-dichlorophenoxyacetate was first converted to a dichlorophenol before dehalogenation occurred. Sewage sludge microorganisms dehalogenated four of seven chlorophenols tested and degraded both phenoxyacetate herbicides by first converting them to the corresponding chlorophenols, but the microorganisms did not transform the chlorobenzoates. In general, the same suite of initial metabolites were produced from a test substrate in all types of samples, as confirmed by cochromatography of the intermediates with authentic material. Aquifer microbiota from a sulfate-reducing site was unable to significantly degrade any of the haloaromatic substrates tested. Biological removal of the sulfate in samples from this site permitted dehalogenation of a model substrate, while stimulation of methanogenesis without removal of sulfate did not. These results demonstrate that dehalogenating microorganisms were present at this site but that their activity was at least partially inhibited by the high sulfate levels. 相似文献
19.
Anaeromyxobacter dehalogenans strain 2CP-C dehalogenatesortho-substituted di- and mono-halogenated phenols and couples this activity to growth. Reductive dehalogenation activity has been reported to be inducible, however,this process has not been studied extensively. In this study, theinduction of reductive dehalogenation activity by strain 2CP-C is characterized. Constitutive 2-chlorophenoldechlorination activity occurs in non-induced fumarate-grown cells, with rates averaging 0.138 mol of Cl- h-1 mg of protein-1. Once induced, these cultures dechlorinate 2-chlorophenol (2-CP) at rates as high as 116 mol of Cl-1 h-1 mg of protein-1. Dechlorination of 2-CP is induced by phenol,2-chlorophenol, 2,4-dichlorophenol, 2,5-dichlorophenol, 2,6-dichlorophenol,and 2-bromophenol. Of the substrates tested, 2-bromophenol shows the highestinduction potential, yielding double the 2-chlorophenol dechlorination rate when compared to other inducing substrates. No induced dechlorination is observed at concentrations less than5 M 2-CP. When fumarate cultures were diluted 100-fold, fumarate reduction rates were reduced roughly according to the dilution factor, while dechlorination rates were similar in fumarate grown cells amended with 2-CP and cells diluted 100-fold prior to the addition of chlorophenol. This indicates that the majority of the fumarate-grown cells in late log phase were not induced when exposed to inducing substrates such as 2-CP. This observation may have ramifications on the success of bioaugmentation using halorespiring bacteria, which traditionally relies on growing culturesusing more readily utilized substrates. The rapid dechlorination rate and unique induction pattern also make strain 2CP-C a promising model organism for understanding the regulationof reductive dehalogenation at the enzymatic level. 相似文献
20.
Tetrachlorohydroquinone dehalogenase catalyzes the reductive dehalogenation of tetrachloro- and trichlorohydroquinone to give 2,6-dichlorohydroquinone in the pathway for degradation of pentachlorophenol by Sphingobium chlorophenolicum. Previous work has suggested that this enzyme may have originated from a glutathione-dependent double bond isomerase such as maleylacetoacetate isomerase or maleylpyruvate isomerase. While some of the elementary steps in these two reactions may be similar, the final step in the dehalogenation reaction, a thiol-disulfide exchange reaction that removes glutathione covalently bound to Cys13, certainly has no counterpart in the isomerization reaction. The thiol-disulfide exchange reaction does not appear to have been evolutionarily optimized. There is little specificity for the thiol; many thiols react at high rates. TCHQ dehalogenase binds the glutathione involved in the thiol-disulfide exchange reaction very poorly and does not alter its pK(a) in order to improve its nucleophilicity. Remarkably, single-turnover kinetic studies show that the enzyme catalyzes this step by approximately 10000-fold. This high reactivity requires an as yet unidentified protonated group in the active site. 相似文献