Alachlor is an aniline herbicide used to control annual grasses and broadleaf weeds in field corn, soybeans, and peanuts. It is a selective systemic herbicide, absorbed by germinating shoots and roots. It works by interfering with the plant's ability to produce protein and elongate roots. When directly applied to soil, it may leach into groundwater and thereby pose a potential health hazard to humans and animals (Sette et al., 2004).
Alachlor is degraded by many soil microorganisms, although no pure or mixed cultures able to extensively degrade or mineralize alachlor have been reported. Bacteria and fungi can degrade alachlor through co-metabolism. Sette et al., (2004) used six highly tolerant streptomycete strains in their studies and identified the main biodegradation products as dechlorinated indole compounds, a quinoline derivative compound and a chlorinated indole derivative. Of all the strains reported to degrade alachlor, strain LS182 did not generate the carcinogenic product 2,6-diethylaniline. Hence, LS182 strain may be the best strain to use in bioremediation of alachlor.
Reactions A-C, below, all occur spontaneously, in water without microbial inocula. These abiotic reactions are predominently hydrolyses, including dehalogenation and amide hydrolysis, but include more complex reactions as well. The alachlor hydrolase reaction is enzyme-mediated, but also occurs at a slower rate abiotically (Sette et al., 2004).
Alachlor can be detoxified by displacement of the chlorine group with a thiol (e.g. glutathione, coenzyme A, cysteine) to produce an alachlor-thiol conjugate. These reactions occur both abiotically and enzymatically via glutathione-S-transferase (GST). Soil microorganisms with GST activity have been shown to product alachlor-cysteine and alachlor-cysteine-glycine conjugates (Zablotowicz et al., 1995). Further enzymatic oxidation of these conjugates produce alachlor-ESA (ethyl sulfonic acid) (Stamper et al., 1998). Possible metabolites of alachlor-ESA found in soil and groundwater include alachlor-OA (oxanilic acid) (Postle et al., 2004) and N-(2,6-Diethylphenyl)-ESA (Thurman et al., 2002).
Tiedje et al., (1975) studied the degradation of alachlor by the soil fungus, Chaetomium globosum, and identified four metabolites: 2-Chloro-2',6'-diethylacetanilide, 2,6-Diethyl-N-(methoxymethyl)aniline, 2,6-Diethylaniline and 1-Chloroacetyl-2,3-dihydro-7-ethylindole.
The following is a text-format Alachlor pathway map. An organism which can initiate the pathway is given, but other organisms may also carry out later steps. Follow the links for more information on compounds or reactions.
Graphical Map(9K) | Graphical Map(7K) | Graphical Map(11K)
Alachlor Alachlor Alachlor
Streptomyces sp. Streptomyces sp. Streptomyces sp.
LS166, LS177, LS182 LS166, LS177 LS166, LS177, LS182
Chaetomium globosum | Chaetomium globosum
| | |
| alachlor | B | alachlor
| hydrolase | (spontaneous) | amidohydrolase
| | |
v v v
2-Chloro- not LS182 2-Hydroxy-2',6'-diethyl- not LS182 2,6-Diethyl-
2',6'-diethylacetanilide ---------+ N-acetanilide +--------- N-(methoxymethyl)aniline
| | | | not C.globosum
| | | | |
| | | 2-hydroxy-2',6'- | |
| 2-chloro-2',6'- | | diethyl-N-acetanilide | |
| diethylacetanilide | | hydrolase | |
| dehydrogenase | | | +-------------+-------------+
| | | | | |
v | v | | 2,6-diethyl- |
1-Chloroacetyl-2,3-dihydro- | [N-(2,6-Diethylphenyl)- | | N-(methoxymethyl) v C
7-ethylindole | 2-hydroxyacetamide] | | aniline dehydrogenase | (spontaneous)
| | | | | |
| 1-chloroacetyl- | | | v v
| 2,3 dihydro- | | N-(2,6-diethylphenyl)- | 7-Ethyl-3- N-(2,6-Diethylphenyl)-
| 7-ethylindole | | 2-hydroxyacetamide | methyl-2-methoxy- methyleneamine
| amidohydrolase | | hydrolase | 2,3-dihydroindole |
| | | | | N-(2,6-diethylphenyl)-
v | v | | methyleneamine
7-Ethylindole +-------------> 2,6-Diethylaniline <----------------+ | dehydrogenase
A 2,6-diethyl- |
(spontaneous) N-(methoxymethyl)aniline v
hydrolase [2-Ethenyl-6-ethyl-
N-methylideneaniline]
|
|
|
+----------------+----------------+
| |
| 2-ethenyl-6-ethyl- |
| N-methylideneaniline v D
| dehydrogenase |
| |
v v
8-Ethylquinoline 7-Ethyl-N-methylindole
Page Author(s): Sujana Mittapalli and Michael Turnbull
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