2,4,6-Trinitrotoluene is a yellow, odorless solid that does not occur naturally in the environment. It is commonly known as TNT and is an explosive used in military shells, bombs, and grenades, in industrial uses, and in underwater blasting. TNT production in the United State occurs solely at military arsenals. Accidental release of TNT has contaminated groundwater and soil at numerous munition manufacturing sites. The U.S. EPA has listed TNT as a priority pollutant and has recommended its removal from contaminated sites. TNT is toxic to algae and invertebrates and chronic exposure to TNT by humans causes harmful health effects, including anemia and abnormal liver function, cataract development, and skin irritation. The EPA has determined that TNT is a possible human carcinogen, based on animal studies. This page shows only its anaerobic pathway. The aerobic degradation of trinitrotoluene is documented elsewhere in the EAWAG-BBD.
Few enzymes have been isolated which catalyze the reactions in these pathways. Indeed, most of the reactions are catalyzed by "non-specific" NAD(P)H dependent nitroreductases and are uncharacterized. The last reduction steps to produce triaminotoluene occur only under anaerobic conditions and enzymes which can catalyze these reactions have been found in Desufovibrio sp., Clostridium pasteurianum, and Moorella thermoacetica. Many of these nitro group reductions are also catalyzed by purified xenobiotic reductase enzyme (Blehert et al., 1999). A disulfite reductase capable of catalyzing the final reduction to triaminotoluene has only been found in Desulfovibrio sp. There are very few example of TNT mineralization or transformation to a compound in intermediate metabolism by a pure bacterial culture. Generally mineralization is only detected with bacterial consortia. Many of the products of TNT biodegradation are highly reactive and covalently bind to cellular components and any solid supports (such as soil) present in the culture. The latter prevents or prolongs the mineralization process, but also hinders a further spread of TNT contaminants. Several authors have noted the formation of, as yet, unidentified compounds from TNT biodegradation. These have not been included in either the aerobic or anaerobic pathway maps. Prof R. Crawford and co-workers have also identified an adduct formed from methyl glyoxyl and triaminotoluene, however they suggest this product is not a main stream pathway intermediate, but a product produced by a side reaction related to clostridial fermentation.
The following is a text-format trinitrotoluene degradation pathway. Organisms which can initiate each pathway are given, however they do not all carry out every pathway reaction. When this is the case, the organisms which can carry out a particular reaction are noted. If no organisms are listed for a reaction, the organism(s) listed for the preceding reaction(s) also carry it out. Follow the links for more information on compounds or reactions.
|--------------------------------------Graphical Map (28K)----------------------------------------|
Trinitrotoluene Trinitrotoluene Trinitrotoluene Trinitrotoluene
C. pasteurianum anaerobic consortia P. savastanoi gram+ strain TNT-32
anaerobic consortia M. thermoacetica Desulfovibrio sp. gram- strain TNT-8
| Desulfovibrio sp. | P. fluorescens
| C. sordellii ATCC 9714 | |
| C. bifermentans KMR-1 | |
| C. bifermentans ATCC 638 | |
| C. sporogenes ATCC 11437 | |
| L. acidophilus | |
| L. casei | |
| L. delbrueckii subsp. lactis | |
| E. coli | |
| S. choleraesuis | |
| | | |
| nitrobenzene | non-specific | non-specific | non-specific
| nitroreductase | NAD(P)H | NAD(P)H | NAD(P)H
| | nitroreductase | nitroreductase | nitroreductase
| | | |
v | | v
4-Hydroxylamino- | | 2-Hydroxylamino-
2,6-dinitrotoluene | | 4,6-dinitrotoluene
| \ | | /
| C. aceto \ | | /
| butylicum \ non-specific | | / non-specific
| \ NAD(P)H | | / NAD(P)H
| nitrobenzene \ nitro- | | / nitroreductase
| nitroreductase \ reductase | | /
| \ | | /
v \ v v /
2,4-Dihydroxyl- 4-Amino-2,6-dinitro- <-- from the --> 2-Amino-4,6-dinitro-
amino-6-nitro- toluene Aerobic TNT Pathway toluene
toluene \ /
| \ /
| non-specific \ / non-specific
v A NAD(P)H \ / NAD(P)H
| nitroreductase \ / nitroreductase
| \ /
v \ /
2-Amino-5-hydroxyl- 2,4-Diamino-
4-hydroxylamino-6- 6-nitrotoluene
nitrotoluene | \
| \ hydrogenase or
| \ carbon monoxide dehydrogenase
B | \
| \
C. sordelli ATCC 9714 | \
C. bifermentans KMR-1 v 2,4-Diamino-6-hydroxyl-
C. bifermentans ATCC 638 | aminotoluene
C. sporogenes ATCC 11437 | /
| /
| / dissimilatory
| / sulfite reductase
| /
v /
2,4,6-Triamino-
toluene
|
| anaerobic consortia
v
| C
|
v
2,4,6-Trihydroxytoluene
|
|
v D
|
|
v
4-Hydroxytoluene
|
|
|
|
|
v
to the
Toluene
Pathway
Page Author(s): Sara McFarlan and Guang Yao
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