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Hanspeter E Kohler - One of the best experts on this subject based on the ideXlab platform.

  • Fate of the herbicides Mecoprop, dichlorprop, and 2,4-D in aerobic and anaerobic sewage sludge as determined by laboratory batch studies and enantiomer-specific analysis
    Biodegradation, 1999
    Co-Authors: Christian Zipper, Christoff Bolliger, Thomas Fleischmann, Marc J.-f. Suter, Werner Angst, Markus D. Müller, Hanspeter E Kohler
    Abstract:

    Aerobic degradation experiments with the racemic mixtures of Mecoprop and dichlorprop revealed that activated sludge collected from the aeration tank of a municipal waste water treatment plant degraded both enantiomers of Mecoprop and dichlorprop within 7 days, albeit in an enantioselective manner; the (S) enantiomers were preferentially degraded. Mecoprop, dichlorprop, and 2,4-D were completely metabolized under aerobic conditions, as shown by the 86–98% elimination of dissolved organic carbon. Under anaerobic conditions, the concentration of 2,4-D decreased exponentially with a first-order reaction rate constant of 0.24 per day and without a lag-phase. After an incubation time of 17 days, 2,4-D was completely removed. 2,4-Dichlorophenol was the main metabolite of anaerobic 2,4-D degradation; only traces of 4-chlorophenol were detected. In contrast, the chiral phenoxypropionic acid herbicides Mecoprop and dichlorprop persisted under anaerobic conditions during 49 days of incubation.

  • microbial transformation of the chiral pollutants Mecoprop and dichlorprop
    1999
    Co-Authors: Hanspeter E Kohler, Kathrin Nickel, Monika Bunk, Christian Zipper
    Abstract:

    Mecoprop and dichlorprop, two chiral herbicides, are enantioselectively degraded by Sphingomonas herbicidovorans MH. Experiments on the biochemistry of Mecoprop and dichlorprop metabolism in this bacterium show that one reason for enantioselectivity is the existence of two distinct α-ketoglutarate-dependent dioxygenases—one that is specific for the R enantiomers and one that is specific for the S enantiomers of Mecoprop and dichlorprop. Uptake experiments with radiolabeled dichlorprop provide evidence that the first step in the degradation of dichlorprop and Mecoprop by strain MH is active transport and that two inducible, proton gradient-driven uptake systems exist—one uptake system for (R)-dichlorprop and (R)-Mecoprop and another one for (S)-dichlorprop and (S)-Mecoprop. This indicates that the enantioselective degradation of Mecoprop and dichlorprop by the soil isolate S. herbicidovorans MH is not only due to enantioselective metabolism but also to enantioselective uptake. Because selective enrichment of one of the enantiomers may occur in the environment it is important to assess the environmental impact of stereoisomers separately. A field study of chiral Mecoprop in a contaminated aquifer downstream of a former waste disposal site in Switzerland supports this notion as the study clearly shows that the R enantiomer enriches during groundwater passage of the landfill leachate that was polluted with racemic Mecoprop. We conclude that enantioselective microbial degradation increases the enantiomeric ratio of (R)- to (S)-Mecoprop and suggest that analysis of enantiomeric ratios of chiral contaminants such as Mecoprop can provide information about in situ biodegradation processes.

  • enantioselective uptake and degradation of the chiral herbicide dichlorprop rs 2 2 4 dichlorophenoxy propanoic acid by sphingomonas herbicidovorans mh
    Journal of Bacteriology, 1998
    Co-Authors: Christian Zipper, Monika Bunk, Alexander J B Zehnder, Hanspeter E Kohler
    Abstract:

    Research on the biodegradation of chiral xenobiotics can provide a better understanding of the processes that govern enantioselectivity in the microbial degradation and environmental fate of stereoisomers. We have examined the microbial degradation of the widely used chiral herbicide Mecoprop [(RS)-2-(4-chloro-2-methylphenoxy)propanoic acid] by a pure bacterial strain that was isolated from soil. This strain, Sphingomonas herbicidovorans MH, can utilize both enantiomers of Mecoprop as sole carbon and energy sources for growth (24). Growth experiments with the pure enantiomers as well as with racemic Mecoprop revealed that the (S) enantiomer disappeared much faster from the culture medium than the (R) enantiomer. Based on these results, we concluded that specific catabolic enzymes must be involved in the degradation of each enantiomer of Mecoprop (24). This view was confirmed by the finding that two α-ketoglutarate-dependent dioxygenases are involved in the enantioselective degradation of Mecoprop in S. herbicidovorans MH, one that is specific for (R)-Mecoprop and one that is specific for (S)-Mecoprop (17). The (S) enantiomer-specific dioxygenase activity is constitutively expressed, whereas the (R) enantiomer-specific enzyme activity is present only when cells grow on the (R) enantiomer. Both enzymes are present in cells grown on the racemic mixture. Extracts of cells grown on complex medium and extracts of cells grown on (S)-Mecoprop contain equally high activities of the (S) enantiomer-specific dioxygenase (17). However, intact cells grown on complex medium show very low oxygen uptake rates with (S)-Mecoprop, whereas (S)-Mecoprop-grown cells show high oxygen consumption with (S)-Mecoprop (24). These findings suggested the existence of specific uptake systems and led us to examine the uptake of phenoxyalkanoic acids by S. herbicidovorans after growth on various substrates. Many aromatic compounds are taken up by bacteria through energy-dependent transport systems (4, 5, 10, 11, 15, 16). The uptake of 4-chlorobenzoate by the coryneform bacterium NTB-1 is inducible and coupled to the proton motive force (4). The uptake of 4-toluene sulfonate by Comamonas testosteroni T-2 is also inducible and shows substrate saturation kinetics (11). Transport of 4-toluene sulfonate is inhibited completely by uncouplers but only marginally by ATPase inhibitors, and the authors proposed that 4-toluene sulfonate is taken up by an inducible secondary proton symport system (11). The uptake of 4-hydroxybenzoate by Pseudomonas putida is driven by the proton motive force, and the gene that encodes a 4-hydroxybenzoate transporter was identified, cloned, and expressed in Escherichia coli. Furthermore, it was found that 4-hydroxybenzoate transport is an integral feature of the β-ketoadipate pathway in P. putida (5, 15, 16). The uptake of the herbicide 2,4-D (2,4-dichlorophenoxyacetic acid) by Ralstonia eutropha JMP134 is inducible, is sensitive to metabolic inhibitors, and shows substrate saturation kinetics (10). Moreover, the authors identified a gene, designated tfdK, whose translation product shows resemblance to transport proteins of the major facilitator superfamily, and they suggested that tfdK encodes the 2,4-D transporter of R. eutropha JMP134. Our results indicate that S. herbicidovorans MH has two distinct uptake systems for chiral phenoxypropionic acid herbicides, one for the (R) enantiomer and another one for the (S) enantiomer of dichlorprop and Mecoprop. Furthermore, evidence was obtained that 2,4-D was taken up by a third transport system.

  • changes in the enantiomeric ratio of r to s Mecoprop indicate in situ biodegradation of this chiral herbicide in a polluted aquifer
    Environmental Science & Technology, 1998
    Co-Authors: Christian Zipper, M Suter, Stefan B Haderlein, Michael Gruhl, Hanspeter E Kohler
    Abstract:

    Leachate samples from a waste disposal site in Switzerland and groundwater samples downstream of the landfill were analyzed for residues of (R)- and (S)-Mecoprop [(R)- and (S)-2-(4-chloro-2-methylphenoxy)propionic acid] by means of enantiomer-specific gas chromatography combined with mass spectrometry. (R)- And (S)-Mecoprop were found at equal concentrations (up to 124 μg/L) in the landfill leachate, indicating that a racemic mixture of Mecoprop leached to the receiving groundwater. Groundwater samples downstream of the landfill contained from <0.001 to 975 μg/L of Mecoprop and 16 out of 31 samples showed a significant excess of (R)-Mecoprop. Sorption of (R)- and (S)-Mecoprop to aquifer matrix and to various reference minerals was generally low and did not discriminate between the Mecoprop enantiomers. We conclude that enantioselective microbial degradation increased the enantiomeric ratio of (R)- to (S)-Mecoprop during groundwater passage of the landfill leachate. Most leachate-affected groundwaters are ...

  • environmental fate of chiral pollutants the necessity of considering stereochemistry
    Chimia, 1997
    Co-Authors: Hanspeter E Kohler, Stephan Muller, W Angst, Walter Giger, C Kanz, Marc J.-f. Suter
    Abstract:

    Many organic compounds regulated by environmental laws are chiral and are released into the environment as racemates. 3-Phenylbutanoic acid and Mecoprop, two chiral pollutants, were enantioselectively degraded by pure cultures of microorganisms. This indicates the importance of assessing the environmental impact of stereoisomers separately, because selective enrichment of one of the enantiomers may occur in the environment. Field studies on the fate of highly polar, chiral compounds, like sulfophenylcarboxylates, are hampered by the lack of appropriate analytical methods for the separation of the enantiomers. Therefore, a method based on capillary electrophoresis with a-cyclodextrin as chiral selector was developed to separate the enantiomers of such compounds. In a field study at a Swiss waste disposal site, the fate of the chiral herbicide Mecoprop was investigated. The enantiomeric ratio of (R)-Mecoprop to (S)-Mecoprop altered during groundwater passage of landfill leachate. This is a strong indication for in situ biodegradation. Our data imply that not only the enantiomers of a chiral drug or pesticide may exert different effects on the biological targets, but also their biodegradation and environmental fate may differ.

Hilary M Lappinscott - One of the best experts on this subject based on the ideXlab platform.

  • biodegradation of the chlorophenoxy herbicide r Mecoprop by alcaligenes denitrificans
    Biodegradation, 1997
    Co-Authors: Vanessa A. Tett, Andrew Willetts, Hilary M Lappinscott
    Abstract:

    An Alcaligenes denitrificans strain capable of utilizing theherbicide (R)-(+)-2(2-methyl-4-chlorophenoxy)propionicacid (Mecoprop) as a sole carbon source was isolated fromsoil and cultured in liquid medium. Crude cell extracts of thebacterium were utilized in spectrophotometric assays toelucidate a biochemical pathway for degradation ofMecoprop. Results indicated a reaction sequence analogousto the degradation of 2,4-dichlorophenoxyacetic acid (2,4-D).GC-MS analysis provided direct evidence for thebiotransformation of Mecoprop to the transient metabolite4-chloro-2-methylphenol (MCP). No NADPH-dependentactivity was observed during this reaction. Pyruvate wasverified as the second product derived from the aliphatic sidechain of Mecoprop. MCP was subsequently transformed to asubstituted catechol by an NADPH-dependentmonooxygenase. When grown on Mecoprop, A.denitrificans was adapted to oxidize catechol and its 4- and3-methylated derivatives indicating the broad substratespecificity of catechol dioxygenase. The microorganism wasdemonstrated to adopt the ortho mechanism of aromaticcleavage which resulted in the formation of2-methyl-4-carboxymethylene but-2-en-4-olide, a reactionintermediate of the β-ketoadipate pathway.

  • enantioselective degradation of the herbicide Mecoprop 2 2 methyl 4 chlorophenoxy propionic acid by mixed and pure bacterial cultures
    FEMS Microbiology Ecology, 1994
    Co-Authors: Vanessa A. Tett, Andrew Willetts, Hilary M Lappinscott
    Abstract:

    A consortium of three bacteria was isolated from top soil through their capacity to utilise the chlorinated, aromatic herbicide Mecoprop as a single growth substrate. The consortium constituted a tight association of Alcaligenes denitrificans, Pseudomonas glycinea and Pseudomonas marginalis. The culture exclusively degraded the (R)-(+)-isomer of the herbicide while the (S)-(−)-enantiomer remained unaffected. The Mecoprop-degrading community could also degrade 2,4-dichlorophenoxyacetic acid, 2-methyl-4-chlorophenoxyacetic acid and racemic 2-phenoxypropionic acid. Initially, no single member of the consortium was able to degrade Mecoprop as a pure culture but after prolonged incubation, A. denitrificans was able to grow on the herbicide as the sole source of carbon and energy.

Christian Zipper - One of the best experts on this subject based on the ideXlab platform.

  • Fate of the herbicides Mecoprop, dichlorprop, and 2,4-D in aerobic and anaerobic sewage sludge as determined by laboratory batch studies and enantiomer-specific analysis
    Biodegradation, 1999
    Co-Authors: Christian Zipper, Christoff Bolliger, Thomas Fleischmann, Marc J.-f. Suter, Werner Angst, Markus D. Müller, Hanspeter E Kohler
    Abstract:

    Aerobic degradation experiments with the racemic mixtures of Mecoprop and dichlorprop revealed that activated sludge collected from the aeration tank of a municipal waste water treatment plant degraded both enantiomers of Mecoprop and dichlorprop within 7 days, albeit in an enantioselective manner; the (S) enantiomers were preferentially degraded. Mecoprop, dichlorprop, and 2,4-D were completely metabolized under aerobic conditions, as shown by the 86–98% elimination of dissolved organic carbon. Under anaerobic conditions, the concentration of 2,4-D decreased exponentially with a first-order reaction rate constant of 0.24 per day and without a lag-phase. After an incubation time of 17 days, 2,4-D was completely removed. 2,4-Dichlorophenol was the main metabolite of anaerobic 2,4-D degradation; only traces of 4-chlorophenol were detected. In contrast, the chiral phenoxypropionic acid herbicides Mecoprop and dichlorprop persisted under anaerobic conditions during 49 days of incubation.

  • microbial transformation of the chiral pollutants Mecoprop and dichlorprop
    1999
    Co-Authors: Hanspeter E Kohler, Kathrin Nickel, Monika Bunk, Christian Zipper
    Abstract:

    Mecoprop and dichlorprop, two chiral herbicides, are enantioselectively degraded by Sphingomonas herbicidovorans MH. Experiments on the biochemistry of Mecoprop and dichlorprop metabolism in this bacterium show that one reason for enantioselectivity is the existence of two distinct α-ketoglutarate-dependent dioxygenases—one that is specific for the R enantiomers and one that is specific for the S enantiomers of Mecoprop and dichlorprop. Uptake experiments with radiolabeled dichlorprop provide evidence that the first step in the degradation of dichlorprop and Mecoprop by strain MH is active transport and that two inducible, proton gradient-driven uptake systems exist—one uptake system for (R)-dichlorprop and (R)-Mecoprop and another one for (S)-dichlorprop and (S)-Mecoprop. This indicates that the enantioselective degradation of Mecoprop and dichlorprop by the soil isolate S. herbicidovorans MH is not only due to enantioselective metabolism but also to enantioselective uptake. Because selective enrichment of one of the enantiomers may occur in the environment it is important to assess the environmental impact of stereoisomers separately. A field study of chiral Mecoprop in a contaminated aquifer downstream of a former waste disposal site in Switzerland supports this notion as the study clearly shows that the R enantiomer enriches during groundwater passage of the landfill leachate that was polluted with racemic Mecoprop. We conclude that enantioselective microbial degradation increases the enantiomeric ratio of (R)- to (S)-Mecoprop and suggest that analysis of enantiomeric ratios of chiral contaminants such as Mecoprop can provide information about in situ biodegradation processes.

  • enantioselective uptake and degradation of the chiral herbicide dichlorprop rs 2 2 4 dichlorophenoxy propanoic acid by sphingomonas herbicidovorans mh
    Journal of Bacteriology, 1998
    Co-Authors: Christian Zipper, Monika Bunk, Alexander J B Zehnder, Hanspeter E Kohler
    Abstract:

    Research on the biodegradation of chiral xenobiotics can provide a better understanding of the processes that govern enantioselectivity in the microbial degradation and environmental fate of stereoisomers. We have examined the microbial degradation of the widely used chiral herbicide Mecoprop [(RS)-2-(4-chloro-2-methylphenoxy)propanoic acid] by a pure bacterial strain that was isolated from soil. This strain, Sphingomonas herbicidovorans MH, can utilize both enantiomers of Mecoprop as sole carbon and energy sources for growth (24). Growth experiments with the pure enantiomers as well as with racemic Mecoprop revealed that the (S) enantiomer disappeared much faster from the culture medium than the (R) enantiomer. Based on these results, we concluded that specific catabolic enzymes must be involved in the degradation of each enantiomer of Mecoprop (24). This view was confirmed by the finding that two α-ketoglutarate-dependent dioxygenases are involved in the enantioselective degradation of Mecoprop in S. herbicidovorans MH, one that is specific for (R)-Mecoprop and one that is specific for (S)-Mecoprop (17). The (S) enantiomer-specific dioxygenase activity is constitutively expressed, whereas the (R) enantiomer-specific enzyme activity is present only when cells grow on the (R) enantiomer. Both enzymes are present in cells grown on the racemic mixture. Extracts of cells grown on complex medium and extracts of cells grown on (S)-Mecoprop contain equally high activities of the (S) enantiomer-specific dioxygenase (17). However, intact cells grown on complex medium show very low oxygen uptake rates with (S)-Mecoprop, whereas (S)-Mecoprop-grown cells show high oxygen consumption with (S)-Mecoprop (24). These findings suggested the existence of specific uptake systems and led us to examine the uptake of phenoxyalkanoic acids by S. herbicidovorans after growth on various substrates. Many aromatic compounds are taken up by bacteria through energy-dependent transport systems (4, 5, 10, 11, 15, 16). The uptake of 4-chlorobenzoate by the coryneform bacterium NTB-1 is inducible and coupled to the proton motive force (4). The uptake of 4-toluene sulfonate by Comamonas testosteroni T-2 is also inducible and shows substrate saturation kinetics (11). Transport of 4-toluene sulfonate is inhibited completely by uncouplers but only marginally by ATPase inhibitors, and the authors proposed that 4-toluene sulfonate is taken up by an inducible secondary proton symport system (11). The uptake of 4-hydroxybenzoate by Pseudomonas putida is driven by the proton motive force, and the gene that encodes a 4-hydroxybenzoate transporter was identified, cloned, and expressed in Escherichia coli. Furthermore, it was found that 4-hydroxybenzoate transport is an integral feature of the β-ketoadipate pathway in P. putida (5, 15, 16). The uptake of the herbicide 2,4-D (2,4-dichlorophenoxyacetic acid) by Ralstonia eutropha JMP134 is inducible, is sensitive to metabolic inhibitors, and shows substrate saturation kinetics (10). Moreover, the authors identified a gene, designated tfdK, whose translation product shows resemblance to transport proteins of the major facilitator superfamily, and they suggested that tfdK encodes the 2,4-D transporter of R. eutropha JMP134. Our results indicate that S. herbicidovorans MH has two distinct uptake systems for chiral phenoxypropionic acid herbicides, one for the (R) enantiomer and another one for the (S) enantiomer of dichlorprop and Mecoprop. Furthermore, evidence was obtained that 2,4-D was taken up by a third transport system.

  • changes in the enantiomeric ratio of r to s Mecoprop indicate in situ biodegradation of this chiral herbicide in a polluted aquifer
    Environmental Science & Technology, 1998
    Co-Authors: Christian Zipper, M Suter, Stefan B Haderlein, Michael Gruhl, Hanspeter E Kohler
    Abstract:

    Leachate samples from a waste disposal site in Switzerland and groundwater samples downstream of the landfill were analyzed for residues of (R)- and (S)-Mecoprop [(R)- and (S)-2-(4-chloro-2-methylphenoxy)propionic acid] by means of enantiomer-specific gas chromatography combined with mass spectrometry. (R)- And (S)-Mecoprop were found at equal concentrations (up to 124 μg/L) in the landfill leachate, indicating that a racemic mixture of Mecoprop leached to the receiving groundwater. Groundwater samples downstream of the landfill contained from <0.001 to 975 μg/L of Mecoprop and 16 out of 31 samples showed a significant excess of (R)-Mecoprop. Sorption of (R)- and (S)-Mecoprop to aquifer matrix and to various reference minerals was generally low and did not discriminate between the Mecoprop enantiomers. We conclude that enantioselective microbial degradation increased the enantiomeric ratio of (R)- to (S)-Mecoprop during groundwater passage of the landfill leachate. Most leachate-affected groundwaters are ...

  • complete microbial degradation of both enantiomers of the chiral herbicide Mecoprop rs 2 4 chloro 2 methylphenoxy propionic acid in an enantioselective manner by sphingomonas herbicidovorans sp nov
    Applied and Environmental Microbiology, 1996
    Co-Authors: Christian Zipper, Kathrin Nickel, W Angst, Hanspeter E Kohler
    Abstract:

    Sphingomonas herbicidovorans MH (previously designated Flavobacterium sp. strain MH) was able to utilize the chiral herbicide (RS)-2-(4-chloro-2-methylphenoxy)propionic acid (Mecoprop) as the sole carbon and energy source. When strain MH was offered racemic Mecoprop as the growth substrate, it could degrade both the (R) and the (S) enantiomer to completion, as shown by biomass formation, substrate consumption, and stoichiometric chloride release. However, the (S) enantiomer disappeared much faster from the culture medium than the (R) enantiomer. These results suggest the involvement of specific enzymes for the degradation of each enantiomer. This view was substantiated by the fact that resting cells of strain MH grown on (S)-Mecoprop were able to degrade the (S) but not the (R) enantiomer of Mecoprop. Accordingly, resting cells of strain MH grown on (R)-Mecoprop preferentially metabolized the (R) enantiomer. Nevertheless, such cells could transform (S)-Mecoprop at low rates. Oxygen uptake rates with resting cells confirmed the above view, as oxygen consumption was strongly dependent on the growth substrate. Cells grown on (R)-Mecoprop showed oxygen uptake rates more than two times higher upon incubation with the (R) than upon incubation with the (S) enantiomer and vice versa.

Jens Aamand - One of the best experts on this subject based on the ideXlab platform.

  • effect of herbicide concentration and organic and inorganic nutrient amendment on the mineralization of Mecoprop 2 4 d and 2 4 5 t in soil and aquifer samples
    Environmental Pollution, 2007
    Co-Authors: Julia R De Lipthay, Sebastian R Sorensen, Jens Aamand
    Abstract:

    Abstract The impact of the herbicide concentration (0.10–10 000 μg kg−1) and addition of organic and inorganic nutrients on Mecoprop, 2,4-D and 2,4,5-T mineralization in aquifer and soil samples was studied in laboratory experiments. Generally, 2,4-D was most rapidly mineralized followed by Mecoprop and 2,4,5-T. A shift from non-growth to growth-linked mineralization kinetics was observed in aquifer sediment with 2,4-D concentrations >0.10 μg kg−1 and Mecoprop concentrations >10.0 μg kg−1. The shift was apparent at higher herbicide concentrations in soil coinciding with a lower bioavailable fraction and a higher herbicide sorption to soil. Herbicide addition did not affect the bacterial density, although 2,4-D and Mecoprop applied at 10 000 μg kg−1 stimulated growth of specific degraders. Generally, nutrient amendments did not stimulate mineralization at the lowest herbicide concentrations. In contrast, the mineralization rate of higher herbicide concentrations was significantly stimulated by the amendment of inorganic nutrients.

  • mineralization of aged atrazine terbuthylazine 2 4 d and Mecoprop in soil and aquifer sediment
    Environmental Toxicology and Chemistry, 2003
    Co-Authors: Helle Johannesen, Jens Aamand
    Abstract:

    The effect of aging of the herbicides atrazine, terbuthylazine, 2,4-D, and Mecoprop on their bioavailability to degrading microorganisms was studied in soil and aquifer sediment. 14 C-ring-labeled herbicide (2.5 mg/kg) was added to sterilized soil or aquifer sediment and stored at 10°C for up to 103 d before inoculation with either the atrazine and terbuthylazine-degrading Pseudomonas sp. strain ADP (atrazine-degrading Pseudomonas) or an enriched culture able to mineralize 2,4-D and Mecoprop. The initial mineralization rate and recovery of 14 CO 2 after 62 to 113 d of incubation were used as measures of the availability of the compounds to the microorganisms. Aging in soil reduced the initial mineralization of atrazine. Thus, only 17% of the added 14 C-atrazine had been mineralized after 21 h of incubation when aged for 88 d as compared with 33% when the atrazine had been aged for 1 d. 14 CO 2 recovery was only 58% after 88 d of aging as compared with 81% when aged for I d. A similar effect of aging was seen with terbuthylazine. With 2,4-D, the effect of aging in soil on mineralization by the enriched culture was much smaller. Aging had no effect on mineralization of Mecoprop in soil or on mineralization of any of the herbicides in aquifer sediment.

  • mineralization of 2 4 d Mecoprop isoproturon and terbuthylazine in a chalk aquifer
    Pest Management Science, 2001
    Co-Authors: Gitte Boggild Kristensen, Sebastian R Sorensen, Jens Aamand
    Abstract:

    The potential to mineralize 2,4-dichlorophenoxyacetic acid (2,4-D), Mecoprop, isoproturon and terbuthylazine was studied in soil and aquifer chalk sampled at an agricultural field near Aalborg, Denmark. Laboratory microcosms were incubated for 258 days under aerobic conditions at 10 °C with soil and chalk from 0.15–4.45 m below the surface. The [ring-U-14C]-labeled herbicides were added to obtain a concentration of 6 µg kg−1 and mineralization was measured as evolved [14C]carbon dioxide. The herbicides were readily mineralized in soil from the plough layer, except for terbuthylazine, which was mineralized only to a limited extent. In the chalk, lag periods of at least 40 days were observed, and a maximum of 51%, 33% and 6% of the added 2,4-D, Mecoprop and isoproturon, respectively, were recovered as [14C]carbon dioxide. Large variations in both rate and extent of mineralization were observed within replicates in chalk. No mineralization of terbuthylazine in chalk was observed. As a measure of the general metabolic activity towards aromatic compounds, [ring-U-14C]-benzoic acid was included. It was readily mineralized at all depths. © 2000 Society of Chemical Industry

  • Mecoprop isoproturon and atrazine in and above a sandy aquifer vertical distribution of mineralization potential
    Environmental Science & Technology, 2000
    Co-Authors: Lise Larsen, Sebastian R Sorensen, Jens Aamand
    Abstract:

    The vertical distribution of the potential to mineralize [ring-U-14C]herbicides was investigated in samples from a sandy aquifer. Mecoprop, isoproturon, or atrazine were added to sediments from 0.0...

Vanessa A. Tett - One of the best experts on this subject based on the ideXlab platform.

  • biodegradation of the chlorophenoxy herbicide r Mecoprop by alcaligenes denitrificans
    Biodegradation, 1997
    Co-Authors: Vanessa A. Tett, Andrew Willetts, Hilary M Lappinscott
    Abstract:

    An Alcaligenes denitrificans strain capable of utilizing theherbicide (R)-(+)-2(2-methyl-4-chlorophenoxy)propionicacid (Mecoprop) as a sole carbon source was isolated fromsoil and cultured in liquid medium. Crude cell extracts of thebacterium were utilized in spectrophotometric assays toelucidate a biochemical pathway for degradation ofMecoprop. Results indicated a reaction sequence analogousto the degradation of 2,4-dichlorophenoxyacetic acid (2,4-D).GC-MS analysis provided direct evidence for thebiotransformation of Mecoprop to the transient metabolite4-chloro-2-methylphenol (MCP). No NADPH-dependentactivity was observed during this reaction. Pyruvate wasverified as the second product derived from the aliphatic sidechain of Mecoprop. MCP was subsequently transformed to asubstituted catechol by an NADPH-dependentmonooxygenase. When grown on Mecoprop, A.denitrificans was adapted to oxidize catechol and its 4- and3-methylated derivatives indicating the broad substratespecificity of catechol dioxygenase. The microorganism wasdemonstrated to adopt the ortho mechanism of aromaticcleavage which resulted in the formation of2-methyl-4-carboxymethylene but-2-en-4-olide, a reactionintermediate of the β-ketoadipate pathway.

  • enantioselective degradation of the herbicide Mecoprop 2 2 methyl 4 chlorophenoxy propionic acid by mixed and pure bacterial cultures
    FEMS Microbiology Ecology, 1994
    Co-Authors: Vanessa A. Tett, Andrew Willetts, Hilary M Lappinscott
    Abstract:

    A consortium of three bacteria was isolated from top soil through their capacity to utilise the chlorinated, aromatic herbicide Mecoprop as a single growth substrate. The consortium constituted a tight association of Alcaligenes denitrificans, Pseudomonas glycinea and Pseudomonas marginalis. The culture exclusively degraded the (R)-(+)-isomer of the herbicide while the (S)-(−)-enantiomer remained unaffected. The Mecoprop-degrading community could also degrade 2,4-dichlorophenoxyacetic acid, 2-methyl-4-chlorophenoxyacetic acid and racemic 2-phenoxypropionic acid. Initially, no single member of the consortium was able to degrade Mecoprop as a pure culture but after prolonged incubation, A. denitrificans was able to grow on the herbicide as the sole source of carbon and energy.