1,4-Dioxane is classified as a probable human carcinogen. It is used as a stabilizer for chlorinated solvents, particularly, 1,1,1-trichloroethane (TCA), and it is formed as a by-product during the manufacture of polyester and various polyethoxylated compounds. Improper disposal of industrial waste and accidental solvent spills have resulted in the contamination of groundwater with 1,4-dioxane. Volatilization and sorption are not significant attenuation mechanisms due to 1,4-dioxane's complete miscibility with water. At present, advanced oxidation processes (AOPs) are the only proven technology for 1,4-dioxane treatment. 1,4-Dioxane was believed to be very resistant to both abiotic and biologically mediated degradation due to its heterocyclic structure with two ether linkages. However, recent studies have shown that 1,4-dioxane can be biodegraded as a sole carbon and energy source, and that cost-effective biological treatment processes can be developed. Future work should be oriented towards the developme...

Occurrence and Treatment of 1,4-Dioxane in Aqueous Environments

1,4-Dioxane is a probable human carcinogen, and an important emerging water contaminant. In this study, the biodegradation of dioxane by 20 bacterial isolates was evaluated, and 13 were found to be capable of transforming dioxane. Dioxane served as a growth substrate for Pseudonocardia dioxanivorans CB1190 and Pseudonocardia benzenivorans B5, with yields of 0.09 g protein g dioxane-1 and 0.03 g protein g dioxane-1, respectively. Cometabolic transformation of dioxane was observed for monooxygenase-expressing strains that were induced with methane, propane, tetrahydrofuran, or toluene including Methylosinus trichosporium OB3b, Mycobacterium vaccae JOB5, Pseudonocardia K1, Pseudomonas mendocina KR1, Ralstonia pickettii PKO1, Burkholderia cepacia G4, and Rhodococcus RR1. Product toxicity resulted in incomplete dioxane degradation for many of the cometabolic reactions. Brief exposure to acetylene, a known monooxygenase inhibitor, prevented oxidation of dioxane in all cases, supporting the hypothesis that monoo...

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Kinetics of 1,4-dioxane biodegradation by monooxygenase-expressing bacteria.

A bacterium designated Pseudonocardia sp. strain ENV478 was isolated by enrichment culturing on tetrahydrofuran (THF) and was screened to determine its ability to degrade a range of ether pollutants. After growth on THF, strain ENV478 degraded THF (63 mg/h/g total suspended solids [TSS]), 1,4-dioxane (21 mg/h/g TSS), 1,3-dioxolane (19 mg/h/g TSS), bis-2-chloroethylether (BCEE) (12 mg/h/g TSS), and methyl tert-butyl ether (MTBE) (9.1 mg/h/g TSS). Although the highest rates of 1,4-dioxane degradation occurred after growth on THF, strain ENV478 also degraded 1,4-dioxane after growth on sucrose, lactate, yeast extract, 2-propanol, and propane, indicating that there was some level of constitutive degradative activity. The BCEE degradation rates were about threefold higher after growth on propane (32 mg/h/g TSS) than after growth on THF, and MTBE degradation resulted in accumulation of tert-butyl alcohol. Degradation of 1,4-dioxane resulted in accumulation of 2-hydroxyethoxyacetic acid (2HEAA). Despite its inability to grow on 1,4-dioxane, strain ENV478 degraded this compound for >80 days in aquifer microcosms. Our results suggest that the inability of strain ENV478 and possibly other THF-degrading bacteria to grow on 1,4-dioxane is related to their inability to efficiently metabolize the 1,4-dioxane degradation product 2HEAA but that strain ENV478 may nonetheless be useful as a biocatalyst for remediating 1,4-dioxane-contaminated aquifers.

http://dzumenvis.nic.in/biodegradation/pdf/biodegradation of ether pollutants.pdf

Biodegradation of ether pollutants by Pseudonocardia sp. strain ENV478

In this study, evidence for two novel metabolic processes catalyzed by a filamentous fungus, Graphium sp. strain ATCC 58400, is presented. First, our results indicate that this Graphium sp. can utilize the widely used solvent diethyl ether (DEE) as the sole source of carbon and energy for growth. The kinetics of biomass accumulation and DEE consumption closely followed each other, and the molar growth yield on DEE was indistinguishable from that with n-butane. n-Butane-grown mycelia also immediately oxidized DEE without the extracellular accumulation of organic oxidation products. This suggests a common pathway for the oxidation of both compounds. Acetylene, ethylene, and other unsaturated gaseous hydrocarbons completely inhibited the growth of this Graphium sp. on DEE and DEE oxidation by n-butane-grown mycelia. Second, our results indicate that gaseous n-alkane-grown Graphium mycelia can cometabolically degrade the gasoline oxygenate methyl tert-butyl ether (MTBE). The degradation of MTBE was also completely inhibited by acetylene, ethylene, and other unsaturated hydrocarbons and was strongly influenced by n-butane. Two products of MTBE degradation, tert-butyl formate (TBF) and tert-butyl alcohol (TBA), were detected. The kinetics of product formation suggest that TBF production temporally precedes TBA accumulation and that TBF is hydrolyzed both biotically and abiotically to yield TBA. Extracellular accumulation of TBA accounted for only a maximum of 25% of the total MTBE consumed. Our results suggest that both DEE oxidation and MTBE oxidation are initiated by cytochrome P-450-catalyzed reactions which lead to scission of the ether bonds in these compounds. Our findings also suggest a potential role for gaseous n-alkane-oxidizing fungi in the remediation of MTBE contamination.

Metabolism of Diethyl Ether and Cometabolism of Methyl tert-Butyl Ether by a Filamentous Fungus, a Graphium sp.

An actinomycete strain (CB1190(T)) was previously isolated from industrial sludge contaminated with 1,4-dioxane. The cells of this culture are Gram-positive and exhibit branching aerial and vegetative mycelium. Analysis of the 16S rRNA gene sequence indicates that the strain belongs to the genus Pseudonocardia, closely related to Pseudonocardia hydrocarbonoxydans, P. sulfidoxydans and P. halophobica. Physiological and biochemical characteristics of CB1190(T) are different from those of other known Pseudonocardia species. The novel organism described here is distinguished by its ability to grow on 1,4-dioxane, which is a probable human carcinogen. This culture can also grow on tetrahydrofuran, gasoline aromatics and several other toxic environmental contaminants. Strain CB1190(T) is capable of fixing dinitrogen. The predominant fatty acids are 16 : 0 iso, 16 : 1 iso cis9 and 17 : 1 iso cis9. The major phospholipid fatty acids are 16 : 0 iso, 16 : 0 10-Me and 17 : 0 10-Me. The peptidoglycan belongs to type A1gamma, meso-diaminopimelic acid. The major menaquinone is MK-8 (H(4)). Mycolic acids are absent. The G+C content is 74 mol%. Based on morphological, physiological, chemotaxonomic and phylogenetic evidence, it is proposed that strain CB1190(T) (=ATCC 55486(T)=DSM 44775(T)) be classified as the type strain of a novel species, Pseudonocardia dioxanivorans sp. nov. Further studies with this organism will provide insights into metabolic pathways, responsible enzymes, kinetics and the fate of 1,4-dioxane in the environment.

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Pseudonocardia dioxanivorans sp. nov., a novel actinomycete that grows on 1,4-dioxane.

An actinomycete capable of sustained aerobic growth on 1,4-dioxane was isolated from a dioxane-contaminated sludge samples. The actinomycete, CB1190, grows on 1,4-dioxane as the sole carbon and energy source with a generation time of approximately 30 h. CB1190 degrades 1,4-dioxane at a rate of 0.33 mg of dioxane min-1 mg of protein-1 and mineralizes 59.5% of the dioxane to CO2. CB1190 also grows with other cyclic and linear ethers as the sole carbon and energy sources, including 1,3-dioxane, 2-methyl-1,3-dioxolane, tetrahydrofuran, tetrahydropyran, diethyl ether, and butyl methyl ether. CB1190 is capable of aerobic autotrophic growth on H2 and CO2.

R E Parales

Papers

Degradation of 1,4-dioxane by an actinomycete in pure culture.