This pathway was contributed by Michael Turnbull, University of Minnesota.
Malathion is an organophosphate pesticide commonly used in the United States for controlling mosquito populations. The toxicity of malathion is low but acute exposure in high doses may cause a variety of symptoms including nausea, dizziness, or confusion. Malaoxon is a potent cholinesterase inhibitor that can be formed from malathion under certain conditions. Exposure to malaoxon can lead to complications in the central nervous system (Edwards, 2006. US Environmental Protection Agency - Prevention, Pesticides and Toxic Substances EPA 738-R-06-030).
The predominant biodegradation pathway for malathion involves formation of mono- and diacid metabolites through carboxylesterase activity. Oxidative desulfurization and demethylation leads to complete mineralization. Other minor routes of metabolism include initial oxidation to remove sulfur and methyl groups (Laveglia and Dahm, 1977).
Pseudomonas aeruginosa AA112 is able to use malathion as a sole carbon source. Abo-Amer (2007) observed the formation of diethylsuccinate and succinate metabolites. The intermediate steps in this pathway have not been characterized. However, the reduction of -SH to -H (diethyl 2-mercaptosuccinate -> diethylsuccinate) may be abiotic (Hebting et al., 2003).
The following is a text-format malathion degradation pathway map. Organisms which can initiate the pathway are given, but other organisms may also carry out later steps. Follow the links for more information on compounds or reactions. This map is also available in graphic format.
Graphical Map (15k) | Graphical Map (11k)
Malathion Malathion Malathion Malathion
Rhizobium spp. Rhizobium spp. Rhizobium spp. Pseudomonas aeruginosa AA112
Arthrobacter sp. Trichoderma viride Trichoderma viride Aspergillus niger
Trichoderma viride Pseudomonas sp. Pseudomonas sp. Penicillium notatum
Pseudomonas sp. | | Rhizoctonia solani
| | | |
malathion | A v malathion | malathion |
esterase | | phosphodiesterase | oxidoreductase |
+----------------------+ | +------------+ |
| | | | | |
| v v | v v
| Malathion Diethyl malate | Desmethyl Malathion Malaoxon
| monocarboxylate | only Ps. aeruginosa
| | | |
| malathion | | |
| monocarboxylate | | malaoxon |
v esterase | | phosphodiesterase |
[Ethanol] <----------------+ | |
| | | |
| v | v
| Malathion | [S-(Diethylsuccinyl)-]
| dicarboxylate | [O-methylphosphorothioate]
v | | |
Intermediary malathion | | S-(diethylsuccinyl)- |
Metabolism dicarboxylate +----------------------+ | O-methylphosphorothioate |
(KEGG) oxidoreductase | | | phosphodiesterase |
| | | |
v v | v
Dimethyl- [Oxaloacetate] | [S-(Diethylsuccinyl)-]
dithiophosphate | | [phosphorothioate]
| | | |
dimethyl- | | | aryldialkyl- |
dithiophosphate | v | phosphatase |
oxidoreductase | Intermediary | |
| Metabolism | |
v (KEGG) | v
Dimethylthiophosphate | [Diethyl 2-mercapto-]
| | +----------------------+ [succinate]
| | | |
dimethylthiophosphate | +---------------------------------------+ dimethylthiophosphate |
phosphodiesterase | | | oxidoreductase B |
+------------------+ | | |
| | | | |
v | | v v
Methylthiophosphate | | Dimethylphosphate Diethylsuccinate
| | | | |
| v v | |
methylthiophosphate +-------------> [Methanol] <--------------+ dimethylphosphate diethylsuccinate |
phosphomonoesterase | | ^ | phosphodiesterase esterase |
| | | | |
v +--------+ | v v
Thiophosphate | | Methylphosphate [Ethylsuccinate]
| | | | |
| v | | |
thiophosphate | to the +-------------------+ methylphosphate ethylsuccinate |
oxidoreductase | C1 Cycle | phosphomonoesterase esterase |
+--------------------+--------------------+ |
| |
| |
v v
Phosphate Succinate
|
|
|
v
Intermediatry
Metabolism
(KEGG)
Page Author(s): Michael Turnbull
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