The oxidative 4-dechlorination of polychlorinated phenols is catalyzed by extracellular fungal lignin peroxidases

Abstract

The extracellular lignin peroxidases (ligninases) of Phanerochaete chrysosporium catalyzed HzOz-dependent spectral changes in several environmentally significant polychlorinated phenols: 2,4-dichloro-, 2,4,5-trichloro-, 2,4,6-trichloro-, and pentachlorophenol. Gas chromatography/mass spectrometry of reduced and acetylated reaction products showed that, in each case, lignin peroxidase catalyzed a 4-dechlorination of the starting phenol to yield a p-benzoquinone. The oxidation of 2,4-dichlorophenol also yielded a dechlorinated coupling dimer, tentatively identified as 2-chloro-6-(2,4-dichlorophenoxy)-p-benzoquinone. Experiments on the stoichiometry of 2,4,6-trichlorophenol oxidation showed that this substrate was quantitatively dechlorinated to give the quinone and inorganic chloride. Hz'*O-labeling experiments on 2,4,6trichlorophenol oxidation demonstrated that water was the source of the new 4-OXO substituent in 2,6-dichloro-p-benzoquinone. Our results indicate a mechanism whereby lignin peroxidase oxidizes a 4-chlorinated phenol to an electrophilic intermediate, perhaps the 4-chlorocyclohexadienone cation. Nucleophilic attack by water and elimination of HCl then ensue at the 4-position, which produces the quinone. Lignin peroxidases have previously been implicated in the degradation by Phanerochaete of several nonphenolic aromatic pollutants [cf. Haemmerli, S. D., Leisola, M. S.

TiO2-soybean peroxidase composite materials as a new photocatalytic system

“…In the case of the SBP/H 2 O 2 system, any other intermediate was identified, but the reaction mixture initially turns from colourless to yellow, indicating the probable production of 2,6-dichloro-1,4-benzoquinone, in agreement with previous data reported for the reaction catalyzed by lignine peroxidase [30] and horseradish peroxidase [31].…”

Degradation of 2,4-dichlorophenol by the lignin-degrading fungus Phanerochaete chrysosporium

“…Both enzymes oxidized 2,4-dichlorophenol (I) to 2-chloro-1,4-benzoquinone (II). The LiP oxidation of 2,4-dichlorophenol (I) to this product has been previously reported (17). However, the results shown in Fig.…”

“…The irregular and recalcitrant nature of lignin and the fact that it contains substructures found in primary pollutants such as phenols, anisoles, biphenyls, and diarylethers led researchers to postulate that the nonspecific ligninolytic system produced by white rot fungi might be capable of oxidatively degrading persistent aromatic pollutants (2,3,16 nols (19,27). In addition, previous work (17,27) demonstrated that LiP could catalyze the first oxidative dechlorination step in the degradation of several chlorinated phenols. However, except for this initial step, fungal chlorophenol degradative pathways have not been previously elucidated.…”

“…However, for the most part, the degradative pathways utilized by P. chrysosporium have not been examined. For example, P. chrysosporium has been reported to mineralize pentachlorophenol (27), whereas only the initial oxidative 4-dechlorination to the corresponding p-quinone by lignin peroxidase (LiP), purified from the extracellular medium of P. chrysosporium, has been demonstrated (17,27). The pathway beyond this initial step has not been elucidated.…”

Role of Autochthonous Filamentous Fungi in Bioremediation of a Soil Historically Contaminated with Aromatic Hydrocarbons

“…strain DABAC 1, likely due to a partial dehalogenation of chlorinated contaminants. This was not surprising since both lignin peroxidase and laccase have been shown to be able to catalyze the oxidative dechlorination of both chlorophenols and chloroanilines (17,28).…”