1,4-Dioxane is used as a stabilizer in chlorinated solvents. It is an emerging water contaminant known to cause respiratory tract and eye irritant. Furthermore, it is considered a possible human carcinogen, having been shown to be one in rats and guinea pigs. The main routes of human exposure are dermal contact, ingestion, and inhalation (DeRosa et al., 1996).
Both P. dioxanivorans CB1190 and P. benzenivorans B5 contain putative dioxane monooxygenases induced by 1,4-dioxane or THF. Other strains are capable of cometabolic degradation after growth on THF, propane, and toluene. Based on intermediates identified during degradation, 1,4-dioxane is likely hydroxylated at an ether-bond-associated carbon atom by monooxygenases, resulting in spontaneous oxidizion and ring cleavage to form 2-hydroxyethoxyacetate. A second monooxygenase attack at either the ortho or para position with respect to the carboxylic acid moiety yields a mixture of two dihydroxyethoxyacetates. Spontaneous protonation of the hemiacetal bond results in the progressive formation of various small organic molecules including ethylene gylcol, glyoxylate, glycoaldehyde, oxalate (not shown), and glycolate (Mahendra et al., 2007).
The fungus Cordyceps sinensis is able to use 1,4-Dioxane as a sole source of carbon. 1,4-Dioxane is converted to two molecules of ethylene glycol via the proposed formation of two hemiacetals at one side of the dioxane molecule by etherase-type reactions (Nakamiya et al., 2005). Ethylene glycol is degraded via intermediary metabolism. Extracellular fungal peroxygenases have also been shown to oxidatively cleave a diverse set of low molecular weight ethers including 1,4-dioxane (Kinne et al., 2009).
The following is a text-format 1,4-Dioxane pathway map. Organisms which can initiate the pathway are given. Follow the links for more information on compounds or reactions. This map is also available in graphic (8k) format.
1,4-Dioxane 1,4-Dioxane Pseudonocardia dioxanivorans CB1190 Cordyceps sinensis Pseudonocardia benzenivorans B5 | | | | v 1,4-dioxane | 1,4-dioxane | etherase | monooxygenase | | | v v Dioxanone Ethylene | Glycol | spontaneous | | A | | | | | v v 2-Hydroxyethoxyacetate Intermediary | Metabolism | (KEGG) +---------------+----------------+ | | | hydroxyethoxyacetate | hydroxyethoxyacetate | monooxygenase | monooxygenase | | v v o-Dihydroxyethoxy- p-Dihydroxyethoxy- acetate acetate | | | spontaneous | spontaneous | B | C | | | | v v Ethylene + Glyoxylate Glycolate + [Glycoaldehyde] Glycol | | | | | | | | | | | v v v v Intermediary Intermediary Intermediary Intermediary Metabolism Metabolism Metabolism Metabolism (KEGG) (KEGG) (KEGG) (KEGG)
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