Toluene is one of the most water soluble aromatic hydrocarbons. Anaerobic toluene mineralization under denitrifying conditions was demonstrated for pure bacterial cultures. This page shows only its anaerobic pathway. The aerobic degradation of toluene is documented elsewhere in the EAWAG-BBD. Anaerobic toluene mineralization is assumed to proceed via benzoate (benzoyl-CoA) as intermediate. The following tentative pathway for anaerobic toluene oxidation to benzoate (benzoyl-CoA) was compiled from Beller and Spormann 1997, J. Bacteriol. 179 (3): 670-676 and Biegert et al. 1996, Eur. J. Biochem. 238 (3):661-668. In vitro studies were conducted using Azoarcus sp. strain T and Thauera aromatica, respectively.
In these studies, benzylsuccinate, E-phenylitaconate, and benzoyl-CoA (benzoate) were identified as intermediates in anaerobic toluene metabolism. Oxidation of benzylsuccinate to E-phenylitaconate is dependent on CoA (succinyl-CoA), suggesting that the true metabolic intermediates may be benzylsuccinyl-CoA and E-phenylitaconyl-CoA. Compounds in brackets were not identified yet but were postulated based on other experiments. Reversibility of individual reactions involved has not been addressed. Activity of E-phenylitaconyl-CoA hydratase was not demonstrated directly.
The following is a text-format toluene degradation (anaerobic) 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.
Toluene
Azoarcus sp. strain T
Thauera aromatica
|
----------->Fumarate--->|
| | benzylsuccinate
| | synthase
| |
| |
| V
| Benzylsuccinate
| |
| | succinyl-CoA:
| | benzylsuccinate
| | CoA-transferase
| |
| V
| Benzylsuccinyl-CoA
| |
| | benzylsuccinyl-CoA
| | dehydrogenase
| |
| V
| E-phenylitaconyl-CoA
| |
| | E-phenylitaconyl-CoA
| | hydratase
| |
| V
| [(Hydroxymethylphenyl)succinyl-CoA]
| |
| |
| V
| |
| | E
| V
| |
^ /|
| / |
| / |
| V |
-------[Succinyl-CoA] |
|
V
Benzoyl-CoA
|
|
|
v
to the
Anaerobic Benzoate
Pathway
Page Author(s): Alfred Spormann and Eva Young
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