Glyphosate, also known by the trade name Roundup, is a broad-spectrum herbicide widely used in the United States and elsewhere. It is moderately biodegradable, largely due to soil microorganisms. It is representative of a broad class of compounds, known as phosphonic acids, which contain a direct carbon-to-phosphorus (C-P) bond. Although the C-P bond is chemically very stable, many bacteria, even enteric bacteria such as Escherichia coli, have the ability to enzymatically cleave the bond to liberate inorganic phosphate.
In almost all studies of glyphosate metabolism, it was the sole source of phosphorous. However the organisms investigated were not capable of using it as a source of carbon or nitrogen. Because the pathway utilizing the intermediate aminomethylphosphonic acid (AMPA) (pathway shown on the right below) has been found in organisms archived prior to the introduction of glyphosate, it has been postulated that the ability to degrade glyphosate is naturally present in the environment (Kertesz et al, 1994). However, the prevalence of the sarcosine intermediate pathway (shown on the left below) in isolates from glyphosate enriched sources (Dick and Quinn, 1995) suggests that this pathway is selected for in these environments, possibly because the pathway is more favorable to the organisms.
Glyphosate kills plants and bacteria by inhibiting the bacterial and plant enzyme enolpyruvylshikimate-phosphate synthase (EPSPS). Monsanto has developed a way to introduce a bacterial gene for a glyphosate-resistant EPSPS into plants, so that glyphosate can be used for weed control on otherwise glyphosate-susceptible crops.
The following is a text-format glyphosate 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 (9k) format.
Glyphosate Glyphosate
Arthrobacter atrocyaneus Geobacillus caldoxylosilyticus T20
Enterobacter aerogenes Flavobacterium sp.
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| C-P lyase | glyphosate
| | dehydrogenase | |
v v
Sarcosine AMPA
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| |
| | C-P lyase
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| |
v v from the
Intermediary Methylamine <---- Carbofuran, Carbaryl,
Metabolism | and N-Oleoyl-N-methyltaurine
(KEGG) | pathways
| methylamine
| dehydrogenase
|
v
Formaldehyde
|
|
|
|
|
v
C1 Metabolic Cycle
Page Author(s): Robyn Wiersema, Michael A. Burns and Doug Hershberger
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