Biotransformation of 2,7-Dichloro- and 1,2,3,4-Tetrachlorodibenzo- p -Dioxin by Sphingomonas wittichii RW1

Abstract

Aerobic biotransformation of the diaryl ethers 2,7-dichlorodibenzo-p-dioxin and 1,2,3,4-tetrachlorodibenzop-dioxin by the dibenzo-p-dioxin-utilizing strain Sphingomonas wittichii RW1, producing corresponding metabolites, was demonstrated for the first time. Our strain transformed 2,7-dichlorodibenzo-p-dioxin, yielding 4-chlorocatechol, and 1,2,3,4-tetrachlorodibenzo-p-dioxin, producing 3,4,5,6-tetrachlorocatechol and 2-methoxy-3,4,5,6-tetrachlorophenol; all of these compounds were unequivocally identified by mass spectrometry both before and after N,O-bis(trimethylsilyl)-trifluoroacetamide derivatization by comparison with authentic standards. Additional experiments showed that strain RW1 formed a second metabolite, 2-methoxy-3,4,5,6-tetrachlorophenol, from the original degradation product, 3,4,5,6-tetrachlorocatechol, by methylation of one of the two hydroxy substituents.Polychlorinated dibenzo-p-dioxins and dibenzofurans are compounds of considerable environmental concern due to their persistence and toxicity (2). These halogenated compounds have become ubiquitous pollutants because they can be accidentally released (10) after they are formed as unwanted by-products during synthesis of haloaromatic compounds, such as agricultural pesticides (3), or during incineration of industrial or domestic wastes (12,16). In addition to diaryl ethertransforming isolates belonging to genera such as Terrabacter (7, 11) and Pseudomonas (7), workers have isolated and characterized several strains belonging to the genus Sphingomonas which are able to use diaryl ethers, such as dibenzofurans and dibenzo-p-dioxins, as sole sources of carbon and energy (for reviews, see references 2 and 21). Some of these isolates are known to be effective biocatalysts, even catabolizing some diand trichlorinated dibenzo-p-dioxins and dibenzofurans (7,9,19). However, aerobic catabolism of 2,7-dichloro-and 1,2,3,4-tetrachlorodibenzo-p-dioxins, yielding the corresponding metabolites, has not been demonstrated previously.Previous studies showed that in Sphingomonas wittichii RW1 the catabolism of dibenzofurans and dibenzo-p-dioxins is initiated by a ring-hydroxylating dioxygenase (1,18,20), which introduces two hydroxy functions in the angular positions of the corresponding diaryl ethers, thereby producing unstable hemiacetals. The intermediate decays in the case of dibenzop-dioxins, spontaneously yielding the corresponding 2,2Ј,3-trihydroxydiphenyl ether, which is then subjected to meta cleavage and enzymatic hydrolysis, yielding catechol and the corresponding C 6 body 2-hydroxy-cis,cis-muconic acid (for reviews, see references 2 and 21 ). However, although recently reported transformation experiments monitoring the disappearance of selected mono-to tetrachlorinated congeners of dibenzofurans and dibenzo-p-dioxins indicated that even some of the tetrachlorodibenzo-p-dioxins are depleted by the metabolic activity of the bacteria employed (15), there is still a lack of information concerning aerobic bacterial catabolism of tetrachlorinated dibenzo-p-d...

Characterization of a C—C Bond Hydrolase fromSphingomonas wittichiiRW1 with Novel Specificities towards Polychlorinated Biphenyl Metabolites

“…Alternatively, it is possible that the physiological substrate of DxnB2 is substituted 8-OH HODPA. For example, it has been reported that S. wittichii RW1 metabolizes 4-chlorodibenzofuran and 2,7-dichlorodibenzo-p-dioxin to form 9-Cl-, 10-Cl-, or 11-Cl-substituted 8-OH HOPDA (1,17). Consistent with this possibility, DxnB2 possessed higher specificity for 9-Cl and 10-Cl HOPDAs than for unchlorinated HOPDA (Table 1).…”

Biodiversity of Dioxin-Degrading Microorganisms and Potential Utilization in Bioremediation.

“…In the case of 2,4,8-TrCDF, 6,8-dichloro-2-methyl-4H-chromen-4-one was produced as the metabolite. Hong et al 89) reported that Sphingomonas wittichii strain RW1 transformed 2,7-DCDD and 1,2,3,4-TCDD to 4-chlorocatechol and 3,4,5,6-tetrachlorocatechol, respectively. A second metabolite, 2-methoxy-3,4,5,6-tetrachlorophenol, was produced from the original degradation product, 3,4,5,6-tetrachlorocatechol, by methylation of one of the two hydroxy substituents.…”

Biotransformation of 1,2,3-Tri- and 1,2,3,4,7,8-Hexachlorodibenzo-p- Dioxin bySphingomonas wittichiiStrain RW1

“…Consequently, numerous studies have been carried out to elucidate the aerobic (7,9,19) bacterial degradation of PCDD/Fs, compounds produced by incineration processes and as unwanted by-products of the synthesis of pesticides and herbicides (4,17). However, naturally occurring microorganisms have evolved to degrade and mineralize many, but by no means all, of these compounds.…”

“…In addition to genera such as Terrabacter (6,14) and Pseudomonas (6), several strains belonging to the genus Sphingomonas were reported to use diaryl ethers such as dibenzofuran and dibenzo-p-dioxin as the sole source of carbon and energy (3). Some of these isolates are examples for effective biocatalysts that can even catabolize some di-, tri-, and tetrachlorinated dibenzo-p-dioxins and dibenzofurans (6,7,9,19). However, the aerobic catabolism of important environmental pollutants such as 1,2,3,7,8-penta-or 1,2,3,4,7,8-hexachlorodibenzo-p-dioxin, giving rise to the formation of corresponding metabolites, has not been demonstrated previously.…”