Reductive dehalogenation of chlorinated dioxins by an anaerobic bacterium

Abstract

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 humans. 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 dehalorespiration. 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.

Regulation of reductive dehalogenase gene transcription in Dehalococcoides mccartyi

“…The D. mccartyi strain CBDB1 is adapted to organohalide respiration with chlorinated aromatic compounds such as different chlorinated benzenes, phenols, biphenyls and even chlorinated dibenzo-p-dioxins [32][33][34][35]. Figure 1 shows three selected chloroaromatic compounds and the dechlorination route observed with strain CBDB1.…”

“…Figure 1 shows three selected chloroaromatic compounds and the dechlorination route observed with strain CBDB1. With regard to the dechlorination of polychlorinated dibenzo-p-dioxins, strain CBDB1 can even dechlorinate the most toxic congeners 1,2,3,7,8-penta-and 2,3,7,8-tetrachlorodibenzo-p-dioxin to 2,7-or 2,8-dichlorodibenzo-p-dioxin (DCDD), resulting in a strong reduction in the toxicity [33]. The transcriptional response of all 32 rdhA genes of strain CBDB1 during dechlorination of 1,2,3-and 1,2,4-trichlorobenzenes (TCBs) was investigated using a combined reverse transcription (RT)-PCR/terminal restriction fragment length polymorphism analysis (t-RFLP) approach [36].…”

Enrichment and isolation of anaerobic microorganisms concerned with reductive degradation of hexachlorobenzene from soils

“…1) Several bacterial groups, e.g., a sulfur-reducing bacterial group such as Desulfitobacterium sp., 2) and phylum Chloroflexi, such as Dehalococcoides sp., 3) were reported to have anaerobic dehalorespiration, which reductively dechlorinated tetrachloroethene, 2) chlorobenzenes, 4) or chlorophenols or dioxins. 5) Here we represent our results on the enrichment and isolation of anaerobic microorganisms, which could degrade various kinds of POPs under anaerobic conditions. 6,7) Materials and Methods 8) The medium used in this study was designated to enrich microorganisms which use halogenated compounds as electron acceptors.…”

Role of “Dehalococcoides” spp. in the Anaerobic Transformation of Hexachlorobenzene in European Rivers

“…A distant relative of Dehalococcoides spp., "Dehalobium chlorocoercia" DF-1, dechlorinates HCB only to 1,3,5-TCB (48). Besides HCB, strain CBDB1 can also degrade polychlorinated dibenzodioxins, ethenes, phenols, and benzenes (1,3,10), whereas strain 195 can also use chlorinated ethenes and ethanes as electron acceptors (14,31). Enzymes catalyzing the reductive dechlorination of HCB have not yet been identified.…”