Dehalococcoides are perhaps the most important and versatile dechlorinators isolated to date.
Microbial Insights (MI) offers CENSUS® qPCR and QuantArray® quantification of Dehaloccoccoides and functional genes responsible for reductive dechlorination of TCE, DCE, and vinyl chloride.
Chlorinated Ethenes (PCE, TCE, DCE, VC)
Dehalococcoides were the first bacterial group isolated and proven to be capable of complete reductive dechlorination of PCE and TCE to ethene. Since then, the presence of Dehalococcoides spp. has been associated with complete reductive dechlorination to ethene at sites across North America and Europe (Hendrickson et al. 2002). In fact, Lu et al. (2006) have proposed using a Dehalococcoides concentration of 1.0E+04 cells/mL as a screening criterion to identify sites where biological reductive dechlorination will proceed at “generally useful” rates.
Functional genes (TCE, DCE, VC)
To confirm the potential for complete reductive dechlorination of PCE and TCE to ethene, MI offers qPCR and QuantArray quantification of the functional genes encoding TCE and vinyl chloride reductase genes (BVC and VCR). In environmental samples, the Dehalococcoides concentration is a great indicator of the potential for complete reductive dechlorination. Analysis of the Microbial Insights Database revealed that ethene production is observed in nearly 80% of samples where Dehalococcoides concentrations are at least 1.0E+04 cells/mL which is in good agreement with the threshold DHC concentration proposed by Lu et al. (2006). However, quantification of the BVC and VCR vinyl chloride reductase genes provides a critical supporting line of evidence in assessing reductive dechlorination and the potential for accumulation of vinyl chloride.
Moreover, quantification of both characterized vinyl chloride reductase genes BVC and VCR is important for assessing vinyl chloride biodegradation. In analysis of results from more than 12,000 groundwater samples in the Microbial Insights Database, the BVC detection frequency (34%) is only slightly lower than that of VCR (40%). Furthermore, median BVC and VCR concentrations are comparable and perhaps most importantly, BVC or VCR can be present at a high concentration in a sample where the other is not detected. In other words, quantification of only VCR or BVC and not both is only looking at half of the story.
While best known for reductive dechlorination of PCE and TCE to ethene, Dehalococcoides strains are also capable of biodegradation of a broad range of chlorinated compounds as described below.
Chlorinated Ethanes (TCA, DCA)
Dehalococcoides spp. are also capable of utilizing 1,2-DCA as a growth supporting electron acceptor producing ethene via dichloroelimination (Maymó-Gatell et al. 1999). However, perhaps the most important reason to perform CENSUS® quantification of Dehalococcoides when evaluating a site impacted by chlorinated ethanes is to assess the potential for the reductive dechlorination of vinyl chloride produced by dichloroelimination of 1,1,2-TCA.
Chlorinated Benzenes (HCB, PeCB, TeCB, TCB)
Although most research has focused on chlorinated ethenes, some strains of Dehalococcoides have been shown to be capable of utilizing a wide range of chlorinated aromatic compounds. Although biodegradation of individual compounds and specific isomers may vary by isolate, Dehalococcoides spp. have been identified which dechlorinate hexachlorobenzene (HCB), pentachlorobenzene (PeCB), all three isomers of tetrachlorobenzene (TeCB), 1,2,4-trichlorobenzene, and 1,2,3-trichlorobenzene to dichlorobenzenes or 1,3,5-trichlorobenzene (Adrian et al. 2000; Jayachandran et al. 2003).
Chlorinated Phenols (PCP, TeCP, TCP, DCP)
Dehalococcoides is a remarkable genus of bacteria which includes strains capable of reductively dechlorinating a broad range of compounds. For example, Dehalococcoides strain CBDB1 is capable of utilizing pentachlorophenol (PCP), all three tetrachlorphenol (TeCP) congeners, all six trichlorophenol (TCP) congeners, and 2,3-dichlorophenol (2,3-DCP). In addition, strain CBDB1 transformed 2,6-DCP and 2,4-DCP at low rates (Adrian et al. 2007). However, the range of compounds utilized as electron acceptors and transformed can be different between various strains of Dehalococcoides. In the same study, Adrian et al. (2007) demonstrated that Dehalococcoides ethenogenes strain 195 dechlorinated a more narrow spectrum of chlorophenols which included 2,3-DCP, 2,3,4-TCP, and 2,3,6-TCP but not other TCPs or PCP.
Adrian L, Hansen SK, Fung JM, Görisch H, Zinder SH (2007) Growth of Dehalococcoides Strains with Chlorophenols as Electron Acceptors. Environmental Science & Technology 41 (7):2318-2323. doi:10.1021/es062076m
Adrian L, Szewzyk U, Wecke J, Gorisch H (2000) Bacterial dehalorespiration with chlorinated benzenes. Nature 408 (6812):580-583
Hendrickson ER, Payne JA, Young RM, Starr MG, Perry MP, Fahnestock S, Ellis DE, Ebersole RC (2002) Molecular Analysis of Dehalococcoides 16S Ribosomal DNA from Chloroethene-Contaminated Sites throughout North America and Europe. Applied and Environmental Microbiology 68 (2):485-495. doi:10.1128/aem.68.2.485-495.2002
Jayachandran G, Görisch H, Adrian L (2003) Dehalorespiration with hexachlorobenzene and pentachlorobenzene by Dehalococcoides sp. strain CBDB1. Archives of Microbiology 180 (6):411-416. doi:10.1007/s00203-003-0607-7
Lu X, Wilson JT, Kampbell DH (2006) Relationship between Dehalococcoides DNA in ground water and rates of reductive dechlorination at field scale. Water Research 40 (16):3131-3140. doi:10.1016/j.watres.2006.05.030
Maymó-Gatell X, Anguish T, Zinder SH (1999) Reductive Dechlorination of Chlorinated Ethenes and 1,2-Dichloroethane by “Dehalococcoides ethenogenes” 195. Applied and Environmental Microbiology 65 (7):3108-3113