“ Dehalococcoides ” sp. Strain CBDB1 Extensively Dechlorinates the Commercial Polychlorinated Biphenyl Mixture Aroclor 1260

Abstract

"Dehalococcoides" sp. strain CBDB1 in pure culture dechlorinates a wide range of PCB congeners with three to eight chlorine substituents. Congener-specific high-resolution gas chromatography revealed that CBDB1 extensively dechlorinated both Aroclor 1248 and Aroclor 1260 after four months of incubation. For example, 16 congeners comprising 67.3% of the total PCBs in Aroclor 1260 were decreased by 64%. We confirmed the dechlorination of 43 different PCB congeners. The most prominent dechlorination products were 2,3,5-chlorinated biphenyl (25-3-CB) and 24-3-CB from Aroclor 1248 and 235-25-CB, 25-25-CB, 24-25-CB, and 235-236-CB from Aroclor 1260. Strain CBDB1 removed flanked para chlorines from 3,4-, 2,4,5-, and 3,4,5-chlorophenyl rings, primarily para chlorines from 2,3,4,5-chlorophenyl rings, primarily meta chlorines from 2,3,4-and 2,3,4,6-chlorophenyl rings, and either meta or para chlorines from 2,3,4,5,6-chlorophenyl rings. The site of attack on the 2,3,4-chorophenyl ring was heavily influenced by the chlorine configuration on the opposite ring. This dechlorination pattern matches PCB Process H dechlorination, which was previously observed in situ both in the Acushnet Estuary (New Bedford, MA) and in parts of the Hudson River (New York). Accordingly, we propose that Dehalococcoides bacteria similar to CBDB1 are potential agents of Process H PCB dechlorination in the environment. This is the first time that a complex naturally occurring PCB dechlorination pattern has been reproduced in the laboratory using a single bacterial strain.

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.…”

PCB dechlorinases revealed at last

“…First, that each enzyme can catalyze the dechlorination of dozens of PCB congeners as well as PCE (1). It was previously established that single pure strains of D. mccartyi could replicate complex patterns of Aroclor 1260 dechlorination that occur in the environment (10,11). However, it was not known whether this dechlorination resulted from a single RDase enzyme or from multiple RDases.…”

“…So far only one other isolate, D. mccartyi GY50, which couples its growth to polybrominated diphenyl ether (or PBDE), shares this PCB RDase. And at least one more entirely distinct PCB RDase must also exist, because D. mccartyi CBDB1 can extensively dechlorinate Aroclor 1260 but it does not have any close relatives of PcbA1, PcbA4, or PcbA5 (10,13).…”

Quantifying Enhanced Microbial Dehalogenation Impacting the Fate and Transport of Organohalide Mixtures in Contaminated Sediments

“…Several studies suggest a role in the natural dechlorination of PCBs by Dehalococcoides spp. and closely related species (Cutter et al, 2001;Fagervold et al, 2005Fagervold et al, , 2007Watts et al, 2005;Bedard et al, 2006Bedard et al, , 2007Yan et al, 2006a, b;Bedard, 2008;Field and Sierra-Alvarez, 2008;Adrian et al, 2009). Two groups in the phylum Chloroflexi are known for their ability of respiratory dehalogenation; one is the o-17 (Cutter et al, 2001) and DF-1 strain clade (group III) and the other is the Dehalococcoides clade (group II) (Bedard, 2008).…”

“…Two groups in the phylum Chloroflexi are known for their ability of respiratory dehalogenation; one is the o-17 (Cutter et al, 2001) and DF-1 strain clade (group III) and the other is the Dehalococcoides clade (group II) (Bedard, 2008). Group II is further separated into three subgroups based on the variable regions 2 and 6 of their 16S rRNA genes; the so-called Cornell, Victoria, and Pinellas subgroups (Adrian et al, 2000(Adrian et al, , 2009Fennell et al, 2004;. Application of halogenated co-substrates as priming compounds ("haloprimers"), bioaugmentation with Dehalococcoides strains, and combined application of haloprimer plus bioaugmentation have been reported to stimulate rates of anaerobic dechlorination (Wu et al, 1997;Bedard et al, 1998Bedard et al, , 2005Bedard et al, , 2007Vargas et al, 2001;Ahn et al, 2005Ahn et al, , 2007Shiang Fu et al, 2005;Winchell and Novak, 2008).…”