Naphthalene is a fused ring bicyclic aromatic hydrocarbon and thus serves as a model for understanding the properties of a large class of environmentally prevalent polycylic aromatic hydrocarbons (PAHs). Naphthalene and its substituted derivatives are commonly found in crude oil and oil products. Certain PAHs are strong human carcinogens leading to widespread interest in the microbial metabolism of these compounds.
Several Pseudomonas species can degrade naphthalene starting wtih 1,2 dioxygenation, shown here in the middle branch (Eaton et al., 1992). Naphthalene dioxygenase, the enzyme which initiates this route of bacterial naphthalene metabolism, is used in a biotechnological process to synthesize the blue jean dye indigo. This versatile enzyme has many other catalytic abilities, which are documented in a table of the Reactions of Naphthalene 1,2-Dioxygenase.
Bacillus thermoleovorans Hamburg 2 initiates naphthalene degradation with dioxygenation at the 2,3 position (Annweiler et al., 2000), shown here in the left branch. The pathway also includes formation of naphthalene as part of the degradation of 1,2-dihydronaphthalene. This is a minor part of 1,2-dihydronaphthalene degradation; the major route is dioxygenation to 1,2-dihydroxy-1,2,3,4-tetrahydronaphthalene (Torok et al., 1995).
The following is a text-format naphthalene 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 (12k) format.
Naphthalene Naphthalene <--------------+ 1,2-Dihydronaphthalene Bacillus thermoleovorans Pseudomonas sp. NCIB 9816-4, G7 | Pseudomonas putida F39/D Hamburg 2 | | Pseudomonas sp. strain NCIB 9816/11 | | naphthalene | | | naphthalene | 1,2-dioxygenase | toluene | naphthalene | 2,3-dioxygenase | | 1,2-dioxygenase | 1,2-dioxygenase | v | | v cis-1,2-Dihydroxy- +--------------------------+ 2,3-Dihydroxy- 1,2-dihydro- naphthalene naphthalene | | | | 1,2-dihydroxy-1,2- | | dihydronaphthalene v | dehydrogenase to the | Anthracene v Pathway 1,2-Dihydroxy- <------ from the Phenanthrene Pathway naphthalene and Carbaryl Pathway | | 1,2-dihydroxy- | naphthalene | dioxygenase | v 2-Hydroxychromene- 2-carboxylate (HCCA) | | 2-hydroxychromene- | 2-carboxylate | isomerase | v trans-o-Hydroxy- benzylidenepyruvate (tHBPA) | | tHBPA | hydratase-aldolase | v Salicylaldehyde | | salicylaldehyde | dehydrogenase | v from the +---------------- Salicylate <---------- Dibenzofuran Pathway | | Fluorene Pathway | salicylate | salicylate 1-Naphthoic Acid Pathway | 5-hydroxylase | hydroxylase Anthracene Pathway | | v v Gentisate Catechol | | | | | | v v Intermediary to the Metabolism Nitrobenzene (KEGG) Pathway
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