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Reductive dehalogenation of chlorinated dioxins by an anaerobic bacterium


Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDDs and PCDFs) are among the most notorious environmental pollutants. Some congeners, particularly those with lateral chlorine substitutions at positions 2, 3, 7 and 8, are extremely toxic and carcinogenic to humans1. One particularly promising mechanism for the detoxification of PCDDs and PCDFs is microbial reductive dechlorination. So far only a limited number of phylogenetically diverse anaerobic bacteria have been found that couple the reductive dehalogenation of chlorinated compounds—the substitution of a chlorine for a hydrogen atom—to energy conservation and growth in a process called dehalorespiration2. Microbial dechlorination of PCDDs occurs in sediments and anaerobic mixed cultures from sediments, but the responsible organisms have not yet been identified or isolated. Here we show the presence of a Dehalococcoides species in four dioxin-dechlorinating enrichment cultures from a freshwater sediment highly contaminated with PCDDs and PCDFs. We also show that the previously described chlorobenzene-dehalorespiring bacterium Dehalococcoides sp. strain CBDB1 (ref. 3) is able to reductively dechlorinate selected dioxin congeners. Reductive dechlorination of 1,2,3,7,8-pentachlorodibenzo-p-dioxin (PeCDD) demonstrates that environmentally significant dioxins are attacked by this bacterium.

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We thank R. Weber for providing standards for 1,2-, 1,3- and 1,4-DiCDD; M. M. Häggblom and R. U. Halden for comments on the manuscript; and H. Ballerstedt for helpful discussion and support. This work was supported by grants of the Land Sachsen-Anhalt and the Deutsche Forschungsgemeinschaft to U.L. and M.B., of the Technische Universität Berlin to L.A. and of the Fonds der Chemischen Industrie to J.R.A.

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Correspondence to Michael Bunge.

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Figure 1: Time course of reductive dechlorination of 25 µM 1,2,3-TrCDD (a), 60 µM 1,2,4-TrCDD (b) and 46 µM 1,2,3,4-TeCDD (c) by Dehalococcoides sp. strain CBDB1.
Figure 2: Formation of dechlorination products from 1,2,3,7,8-PeCDD.
Figure 3: Proposed pathways of reductive dechlorination of spiked 1,2,3,4-TeCDD (a) and 1,2,3,7,8-PeCDD (b) by a pure culture of Dehalococcoides sp. strain CBDB1.


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