anaerobic dehalogenation of halogenated organic compounds

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Mole % 510 Max M. Häggblom et al. rdh61 rdh63 Dehalococcoides ethenogenes (Tce A) Dehalococcoides sp. VS Desulfitobacterium hafniense (CprA) Paleta creek2 Paleta creek1 85 65 Desulfitobacterium dehalogenans (CprA ) 63 79 35 Sulfurospirillum multivorans (PceA) 73 33 97 SpongeE47 Desulfitobacterium sp. Y51 (Pce A) 100 100 0.1 rdh81A E36 E32 E411 Sponge group 2 E42 E34 E41 E310 E29 E37 E45 Sponge group 1 Figure 2. Phylogenetic tree of deduced partial amino acid sequences of reductive dehalogenases. Reference bar indicates 10 amino acid exchanges per 100 amino acids. sulfate inhibits reductive dechlorination of PCDDs (Vargas et al., 2001) and PCBs (Alder et al., 1993; Zwiernik et al., 1998). It is at the same time interesting to note that some of the dehalogenating organisms that have been characterized are themselves sulfate reducers (DeWeerd et al., 1991; Boyle et al., 1999c; Ahn et al., unpublished). 100 90 80 70 60 50 40 30 20 10 0 1,2,3,4-TeCDD 1,2,4-TriCDD 1,3-DCDD 2-MCDD (+) 2BP (-) 2BP (+) Sulfate (+)2BP (+) Sulfate (-)2BP Figure 3. Mole % 1,2,3,4-TeCDD and its dechlorination daughter products in Paleta Creek sediment under methanogenic and sulfidogenic conditions with and without the addition of 2-bromophenol (from Ahn et al., 2005).
Anaerobic Dehalogenation of Halogenated Organic Compounds 511 3. DEHALOCOCCOIDES ETHENOGENES DECHLORINATES DIVERSE CHLORINATED AROMATIC POLLUTANTS Dehalococcoides ethenogenes strain 195 dechlorinates tetrachloroethene to vinyl chloride and ethene and its genome has been found to contain up to 17 dehalogenase gene homologues (Seshadri et al., 2005) suggesting diverse dehalogenation potential. Detection of multiple dehalogenase homologs in other strains (Hölsher et al., 2004) provides further evidence for the metabolic versatility of this phylogenetic group. Within the Chloroflexi, which includes both Dehalococcoides spp. and other yet to be described genera, there appears to be several strains with the ability to reductively dechlorinate PCBs and other halogenated compounds as electron acceptors (Wu et al., 2002a; Bunge et al., 2003; Watts et al., 2001; Miller et al., 2005). We have demonstrated that D. ethenogenes strain 195 has the potential to dechlorinate many different types of chlorinated aromatic compounds, in addition to its known chloroethene respiratory electron acceptors (Fennell et al., 2004b). D. ethenogenes strain 195 dechlorinated 1,2,3,4- tetrachlorodibenzo-p-dioxin to a mixture of 1,2,4-trichlorodibenzo-p-dioxin and 1,3- dichlorodibenzo-p-dioxin (Figure 4). 2,3,4,5,6-Pentachlorobiphenyl was dechlorinated to 2,3,4,6- and/or 2,3,5,6-tetrachlorobiphenyl and 2,4,6- trichlorobiphenyl. 1,2,3,4-Tetrachloronaphthalene was dechlorinated primarily to an unidentified dichloronaphthalene congener. Results obtained after re-amendment of cultures with PCE suggest that the dehalogenation observed was not necessarily dependent on on-going PCE dehalorespiration since no concomitant increase in the rate of chloroaromatic dechlorination was observed. The ability of D. ethenogenes strain 195 to dehalogenate such a diverse array of organohalides is significant given the prevalence of Dehalococcoides-like organisms in the environment. Bunge et al. (2003) have shown that Dehalococcoides sp. strain CBDB1, which was originally cultivated on trichlorobenzene (Adrian et al., 2000), dehalogenates and sustains growth on chlorinated dioxins. Highly enriched cultures containing strains DF-1 and o-17, bacteria distantly related to Dehalococcoides, are able to dehalogenate chlorinated biphenyls (Wu et al., 2002a; Cutter et al., 2001) and DF-1 also dechlorinates the chlorinated benzenes (Wu et al., 2002b). Aside from these reports, little is known about the anaerobic microorganisms that mediate reductive dechlorination of PCDD/Fs, which is required to initiate complete degradation of highly chlorinated congeners (Toussaint et al., 1998; Gruden et al., 2003), or how to enhance the growth of these organisms under field conditions. Microbial reductive
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anaerobic dehalogenation of halogenated organic compounds

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