Complete dechlorination of tetrachloroethene to ethene in presence of methanogenesis and acetogenesis by an anaerobic sediment microcosm

An anaerobic consortium taken from brackish sediments, enriched byPCE/CH₃OH sequential feeding, was capable of completely dechlorinating tetrachloroethene(PCE) to ethene (ETH). In batch experiments, PCE (0.5 mM) was dechlorinated to ethene (ETH) in approximately 75 h with either CH₃OH or H₂ as the electron donor. When VC (0.5 mM) was added instead of PCE it was dechlorinated without any initial lag by the PCE/CH₃OHenriched consortium, although at a lower dechlorination rate. In batch tests H₂ could readilyreplace CH₃OH for supporting PCE dechlorination, with a similar PCE dechlorination rate andproduct distribution with respect to those observed with methanol. This indicates that H₂ productionduring CH₃OH fermentation was not the rate-limiting step of PCE or VC dechlorination.Acetogenesis was the predominant activity when methanol was present. A remarkable homoacetogenicactivity was also observed when hydrogen was supplied instead of methanol.     

Reductive dechlorination of high concentrations of tetrachloroethene to ethene by an anaerobic enrichment culture in the absence of methanogenesis.

Tetrachloroethene, also known as perchloroethylene (PCE), is a common groundwater contaminant throughout the United States. The incomplete reductive dechlorination of PCE--resulting in accumulations of trichloroethene, dichloroethene isomers, and/or vinyl chloride--has been observed by many investigators in a wide variety of methanogenic environments. Previous mixed-culture studies have demonstrated that complete dechlorination to ethene is possible, although the final dechlorination step from vinyl chloride to ethene is rate limiting, with significant levels of vinyl chloride typically persisting. In this study, anaerobic methanol-PCE enrichment cultures which proved capable of dechlorinating high concentrations PCE to ethene were developed. Added concentrations of PCE as high as 550 microM (91-mg/liter nominal concentration; approximately 55-mg/liter actual aqueous concentration) were routinely dechlorinated to 80% ethene and 20% vinyl chloride within 2 days at 35 degrees C. The methanol level used was approximately twice that needed for complete dechlorination of PCE to ethene. The observed transformations occurred in the absence of methanogenesis, which was apparently inhibited by the high concentrations of PCE. When incubation was allowed to proceed for as long as 4 days, virtually complete conversion of PCE to ethene resulted, with less than 1% persisting as vinyl chloride. An electron balance demonstrated that methanol consumption was completely accounted for by dechlorination (31%) and acetate production (69%). The high volumetric rates of PCE dechlorination (up to 275 mumol/liter/day) and the relatively large fraction (ca. one-third) of the supplied electron donor used for dechlorination suggest that reductive dechlorination could be exploited for bioremediation of PCE-contaminated sites.     

Reductive dechlorination of high concentrations of tetrachloroethene to ethene by an anaerobic enrichment culture in the absence of methanogenesis.

Tetrachloroethene, also known as perchloroethylene (PCE), is a common groundwater contaminant throughout the United States. The incomplete reductive dechlorination of PCE--resulting in accumulations of trichloroethene, dichloroethene isomers, and/or vinyl chloride--has been observed by many investigators in a wide variety of methanogenic environments. Previous mixed-culture studies have demonstrated that complete dechlorination to ethene is possible, although the final dechlorination step from vinyl chloride to ethene is rate limiting, with significant levels of vinyl chloride typically persisting. In this study, anaerobic methanol-PCE enrichment cultures which proved capable of dechlorinating high concentrations PCE to ethene were developed. Added concentrations of PCE as high as 550 microM (91-mg/liter nominal concentration; approximately 55-mg/liter actual aqueous concentration) were routinely dechlorinated to 80% ethene and 20% vinyl chloride within 2 days at 35 degrees C. The methanol level used was approximately twice that needed for complete dechlorination of PCE to ethene. The observed transformations occurred in the absence of methanogenesis, which was apparently inhibited by the high concentrations of PCE. When incubation was allowed to proceed for as long as 4 days, virtually complete conversion of PCE to ethene resulted, with less than 1% persisting as vinyl chloride. An electron balance demonstrated that methanol consumption was completely accounted for by dechlorination (31%) and acetate production (69%). The high volumetric rates of PCE dechlorination (up to 275 mumol/liter/day) and the relatively large fraction (ca. one-third) of the supplied electron donor used for dechlorination suggest that reductive dechlorination could be exploited for bioremediation of PCE-contaminated sites.     

A highly purified enrichment culture couples the reductive dechlorination of tetrachloroethene to growth.

A microscopically pure enrichment culture of a gram-negative anaerobic bacterium, in the present article referred to as PER-K23, was isolated from an anaerobic packed-bed column in which tetrachloroethene (PCE) was reductively transformed to ethane via trichloroethene (TCE), cis-1,2-dichloroethene (cis-1,2-DCE), chloroethene, and ethene. PER-K23 catalyzes the dechlorination of PCE via TCE to cis-1,2-DCE and couples this reductive dechlorination to growth. H2 and formate were the only electron donors that supported growth with PCE or TCE as an electron acceptor. The culture did not grow in the absence of PCE or TCE. Neither O2, NO3-, NO2-, SO4(2-), SO3(2-), S2O3(2-), S, nor CO2 could replace PCE or TCE as an electron acceptor with H2 as an electron donor. Also, organic electron acceptors such as acetoin, acetol, dimethyl sulfoxide, fumarate, and trimethylamine N-oxide and chlorinated ethanes, DCEs, and chloroethene were not utilized. PER-K23 was not able to grow fermentatively on any of the organic compounds tested. Transferring the culture to a rich medium revealed that a contaminant was still present. Dechlorination was optimal between pH 6.8 and 7.6 and a temperature of 25 to 35 degrees C. H2 consumption was paralleled by chloride production, PCE degradation, cis-1,2-DCE formation, and growth of PER-K23. Electron balances showed that all electrons derived from H2 or formate consumption were recovered in dechlorination products and biomass. Exponential growth could be achieved only in gently shaken cultures.(ABSTRACT TRUNCATED AT 250 WORDS)     

Reductive dechlorination of tetrachloroethene to cis-1, 2-dichloroethene by a thermophilic anaerobic enrichment culture.

Thermophilic anaerobic biodegradation of tetrachloroethene (PCE) was investigated with various inocula from geothermal and nongeothermal areas. Only polluted harbor sediment resulted in a stable enrichment culture that converted PCE via trichloroethene to cis-1, 2-dichloroethene at the optimum temperature of 60 to 65 degrees C. After several transfers, methanogens were eliminated from the culture. Dechlorination was supported by lactate, pyruvate, fructose, fumarate, and malate as electron donor but not by H2, formate, or acetate. Fumarate and L-malate led to the highest dechlorination rate. In the absence of PCE, fumarate was fermented to acetate, H2, CO2, and succinate. With PCE, less H2 was formed, suggesting that PCE competed for the reducing equivalents leading to H2. PCE dechlorination, apparently, was not outcompeted by fumarate as electron acceptor. At the optimum dissolved PCE concentration of approximately 60 microM, a high dechlorination rate of 1.1 micromol h-1 mg-1 (dry weight) was found, which indicates that the dechlorination is not a cometabolic activity. Microscopic analysis of the fumarate-grown culture showed the dominance of a long thin rod. Molecular analysis, however, indicated the presence of two dominant species, both belonging to the low-G+C gram positives. The highest similarity was found with the genus Dehalobacter (90%), represented by the halorespiring organism Dehalobacter restrictus, and with the genus Desulfotomaculum (86%).     

Complete reductive dechlorination and mineralization of pentachlorophenol by anaerobic microorganisms

Anaerobically digested municipal sewage sludge which had been acclimated to monochlorophenol degradation for more than 2 years was shown to degrade pentachlorophenol (PCP). Di-, tri-, and tetrachlorophenols accumulated when PCP was added to the individual acclimated sludges. When the 2-chlorophenol- (2-CP), 3-CP-, and 4-CP-acclimated sludges were mixed in equal volumes, PCP was completely dechlorinated. The same results were obtained in sludge acclimated to the three monochlorophenol isomers simultaneously. With repeated PCP additions, 3,4,5,-trichlorophenol, 3,5-dichlorophenol, and 3-CP accumulated in less than stoichiometric amounts. All chlorinated compounds disappeared after PCP additions were stopped. All chlorinated compounds disappeared after PCP additions were stopped. Incubations with [14C]PCP resulted in 66% of the added 14C being mineralized to 14CO2 and 14CH4. Technical-grade PCP was found to be degraded initially at a rate very similar to that of reagent-grade PCP, but after repeated additions, the technical PCP was degraded more slowly. Pentabromophenol was also rapidly degraded by the mixture of acclimated sludges. These results clearly show the complete reductive dechlorination of PCP by the combined activities of three chlorophenol-degrading populations.     

Reductive dechlorination of tetrachloroethene to ethene by a two-component enzyme pathway

Two membrane-bound, reductive dehalogenases that constitute a novel pathway for complete dechlorination of tetrachloroethene (perchloroethylene [PCE]) to ethene were partially purified from an anaerobic microbial enrichment culture containing Dehalococcoides ethenogenes 195. When titanium (III) citrate and methyl viologen were used as reductants, PCE-reductive dehalogenase (PCE-RDase) (51 kDa) dechlorinated PCE to trichloroethene (TCE) at a rate of 20 micromol/min/mg of protein. TCE-reductive dehalogenase (TCE-RDase) (61 kDa) dechlorinated TCE to ethene. TCE, cis-1,2-dichloroethene, and 1,1-dichloroethene were dechlorinated at similar rates, 8 to 12 micromol/min/mg of protein. Vinyl chloride and trans-1,2-dichloroethene were degraded at rates which were approximately 2 orders of magnitude lower. The light-reversible inhibition of TCE-RDase by iodopropane and the light-reversible inhibition of PCE-RDase by iodoethane suggest that both of these dehalogenases contain Co(I) corrinoid cofactors. Isolation and characterization of these novel bacterial enzymes provided further insight into the catalytic mechanisms of biological reductive dehalogenation.     

Complete reductive dechlorination and mineralization of pentachlorophenol by anaerobic microorganisms.

Anaerobically digested municipal sewage sludge which had been acclimated to monochlorophenol degradation for more than 2 years was shown to degrade pentachlorophenol (PCP). Di-, tri-, and tetrachlorophenols accumulated when PCP was added to the individual acclimated sludges. When the 2-chlorophenol- (2-CP), 3-CP-, and 4-CP-acclimated sludges were mixed in equal volumes, PCP was completely dechlorinated. The same results were obtained in sludge acclimated to the three monochlorophenol isomers simultaneously. With repeated PCP additions, 3,4,5,-trichlorophenol, 3,5-dichlorophenol, and 3-CP accumulated in less than stoichiometric amounts. All chlorinated compounds disappeared after PCP additions were stopped. All chlorinated compounds disappeared after PCP additions were stopped. Incubations with [14C]PCP resulted in 66% of the added 14C being mineralized to 14CO2 and 14CH4. Technical-grade PCP was found to be degraded initially at a rate very similar to that of reagent-grade PCP, but after repeated additions, the technical PCP was degraded more slowly. Pentabromophenol was also rapidly degraded by the mixture of acclimated sludges. These results clearly show the complete reductive dechlorination of PCP by the combined activities of three chlorophenol-degrading populations.     

Complete degradation of tetrachloroethene by combining anaerobic dechlorinating and aerobic methanotrophic enrichment cultures

 Degradation of tetrachloroethene (perchloroethylene, PCE) was investigated by combining the metabolic abilities of anaerobic bacteria, capable of reductive dechlorination of PCE, with those of aerobic methanotrophic bacteria, capable of co-metabolic degradation of the less-chlorinated ethenes formed by reductive dechlorination of PCE. Anaerobic communities reductively dechlorinating PCE, trichloroethene (TCE) and dichloroethenes were enriched from various sources. The maximum rates of dechlorination observed for various chloroethenes in these batch enrichments were: PCE to TCE (341 μmol l^-1 day^-1), TCE to cis-dichloroethene (159 μmol l^-1 day^-1), cis-dichloroethene to chloroethene (99 μmol l^-1 day^-1) and trans-dichloroethene to chloroethene (22 μmol l^-1 day^-1). A mixture of these enrichments was inoculated into an anoxic fixed-bed upflow column. In this column PCE was converted mainly into cis-1, 2-dichloroethene, small amounts of TCE and chloroethene, and chloride. Enrichments of aerobic methanotrophic bacteria were grown in an oxic fixed-bed downflow column. Less-chlorinated ethenes, formed in the anoxic column, were further metabolized in this oxic methanotrophic column. On the basis of analysis of chloride production and the disappearance of chlorinated ethenes it was demonstrated that complete degradation of PCE was possible by combining these two columns. Operation of the two-column system under various process conditions indicated that the sensitivity of the methanotrophic bacteria to chlorinated intermediates represented the bottle-neck in the sequential anoxic/oxic degradation process of PCE. Received: 24 October 1994 / Received revision: 20 January 1995 / Accepted: 23 January 1995     

Complete biological reductive transformation of tetrachloroethene to ethane.

Reductive dechlorination of tetrachloroethene (perchloroethylene; PCE) was observed at 20 degrees C in a fixed-bed column, filled with a mixture (3:1) of anaerobic sediment from the Rhine river and anaerobic granular sludge. In the presence of lactate (1 mM) as an electron donor, 9 microM PCE was dechlorinated to ethene. Ethene was further reduced to ethane. Mass balances demonstrated an almost complete conversion (95 to 98%), with no chlorinated compounds remaining (less than 0.5 micrograms/liter). When the temperature was lowered to 10 degrees C, an adaptation of 2 weeks was necessary to obtain the same performance as at 20 degrees C. Dechlorination by column material to ethene, followed by a slow ethane production, could also be achieved in batch cultures. Ethane was not formed in the presence of bromoethanesulfonic acid, an inhibitor of methanogenesis. The high dechlorination rate (3.7 mumol.l-1.h-1), even at low temperatures and considerable PCE concentrations, together with the absence of chlorinated end products, makes reductive dechlorination an attractive method for removal of PCE in bioremediation processes.     

Hydrogen as an electron donor for dechlorination of tetrachloroethene by an anaerobic mixed culture.

Hydrogen served as an electron donor in the reductive dechlorination of tetrachloroethene to vinyl chloride and ethene over periods of 14 to 40 days in anaerobic enrichment cultures; however, sustained dechlorination for more extended periods required the addition of filtered supernatant from a methanol-fed culture. This result suggests a nutritional dependency of hydrogen-utilizing dechlorinators on the metabolic products of other organisms in the more diverse, methanol-fed system. Vancomycin, an inhibitor of cell wall synthesis in eubacteria, was found to inhibit acetogenesis when added at 100 mg/liter to both methanol-fed and hydrogen-fed cultures. The effect of vancomycin on dechlorination was more complex. Methanol could not sustain dechlorination when vancomycin inhibited acetogenesis, while hydrogen could. These results are consistent with a model in which hydrogen is the electron donor directly used for dechlorination by organisms resistant to vancomycin and with the hypothesis that the role of acetogens in methanol-fed cultures is to metabolize a portion of the methanol to hydrogen. Methanol and other substrates shown to support dechlorination in pure and mixed cultures may merely serve as precursors for the formation of an intermediate hydrogen pool. This hypothesis suggests that, for bioremediation of high levels of tetrachloroethene, electron donors that cause the production of a large hydrogen pool should be selected or methods that directly use H2 should be devised.     

Complete biological reductive transformation of tetrachloroethene to ethane.

Reductive dechlorination of tetrachloroethene (perchloroethylene; PCE) was observed at 20 degrees C in a fixed-bed column, filled with a mixture (3:1) of anaerobic sediment from the Rhine river and anaerobic granular sludge. In the presence of lactate (1 mM) as an electron donor, 9 microM PCE was dechlorinated to ethene. Ethene was further reduced to ethane. Mass balances demonstrated an almost complete conversion (95 to 98%), with no chlorinated compounds remaining (less than 0.5 micrograms/liter). When the temperature was lowered to 10 degrees C, an adaptation of 2 weeks was necessary to obtain the same performance as at 20 degrees C. Dechlorination by column material to ethene, followed by a slow ethane production, could also be achieved in batch cultures. Ethane was not formed in the presence of bromoethanesulfonic acid, an inhibitor of methanogenesis. The high dechlorination rate (3.7 mumol.l-1.h-1), even at low temperatures and considerable PCE concentrations, together with the absence of chlorinated end products, makes reductive dechlorination an attractive method for removal of PCE in bioremediation processes.     

Total reductive dechlorination of chlorobenzenes to benzene by a methanogenic mixed culture enriched from Saale river sediment

 A methanogenic mixed culture enriched from Saale river sediment was able to transform all chlorobenzenes by reductive dechlorination via monochlorobenzene to unsubstituted benzene after a short lag phase of only 1 week. The formation of benzene was confirmed by GC/MS in pentane extracts of the sludge samples, as well as in the headspace gas of the batch cultures. The spectra of substrate utilization of the adapted cultures depended mainly on the substrates used for adaptation. Sediment microbes that had been adapted with a mixture of the three isomers of trichlorobenzene offered the widest spectrum for the utilization of chlorobenzenes in all chlorine stages. Reductive dechlorination was stimulated when the mixed cultures were supplemented with pyruvate and methanol. Received: 17 July 1995/Received revision: 11 December 1995/Accepted: 18 December 1995     

Hydrogen as an electron donor for dechlorination of tetrachloroethene by an anaerobic mixed culture.

Hydrogen served as an electron donor in the reductive dechlorination of tetrachloroethene to vinyl chloride and ethene over periods of 14 to 40 days in anaerobic enrichment cultures; however, sustained dechlorination for more extended periods required the addition of filtered supernatant from a methanol-fed culture. This result suggests a nutritional dependency of hydrogen-utilizing dechlorinators on the metabolic products of other organisms in the more diverse, methanol-fed system. Vancomycin, an inhibitor of cell wall synthesis in eubacteria, was found to inhibit acetogenesis when added at 100 mg/liter to both methanol-fed and hydrogen-fed cultures. The effect of vancomycin on dechlorination was more complex. Methanol could not sustain dechlorination when vancomycin inhibited acetogenesis, while hydrogen could. These results are consistent with a model in which hydrogen is the electron donor directly used for dechlorination by organisms resistant to vancomycin and with the hypothesis that the role of acetogens in methanol-fed cultures is to metabolize a portion of the methanol to hydrogen. Methanol and other substrates shown to support dechlorination in pure and mixed cultures may merely serve as precursors for the formation of an intermediate hydrogen pool. This hypothesis suggests that, for bioremediation of high levels of tetrachloroethene, electron donors that cause the production of a large hydrogen pool should be selected or methods that directly use H2 should be devised.     

Specific removal of chlorine from the ortho-position of halogenated benzoic acids by reductive dechlorination in anaerobic enrichment cultures

Anaerobic enrichment cultures catalysing the reductive dechlorination of chlorinated benzoic acids were obtained from three fresh-water sediments collected from seven different locations. Sub-cultures from these enrichments specifically removed ortho-substituted chlorine from 2,3,6-, 2,3,5- and 2,4,6-trichlorobenzoic acid, yielding chloride and 2,5-, 3,5-, and 2,4-dichlorobenzoic acids, respectively. These reductive dehalogenations were stimulated by the addition of benzoate and/or volatile organic acids. In one of these enrichments dehalogenation of ortho- and/or para-chlorine substituents was also observed from 2,3-, 2,4-, 2,5-, and 3,4-dichlorobenzoic acid, yielding 3- and 4-chlorobenzoate. Removal of meta-chlorines was not observed in any of the enrichments.     

Comparative studies on tetrachloroethene reductive dechlorination mediated by Desulfitobacterium sp. strain PCE-S

Tetrachloroethene reductive dechlorination was studied with cell extracts of a newly isolated, tetrachloroethene-utilizing bacterium, Desulfitobacterium sp. strain PCE-S. Tetrachloroethene dehalogenase mediated the reductive dechlorination of tetrachloroethene and trichloroethene to cis-1,2-dichloroethene with artificial electron donors such as methyl viologen. The chlorinated aromatic compounds tested so far were not reduced. A low-potential electron donor (E ₀′ < –0.4 V) was required for tetrachloroethene reduction. The enzyme in its reduced state was inactivated by propyl iodide and reactivated by light, indicating the involvement of a corrinoid in reductive tetrachloroethene dechlorination. Received: 28 April 1997 / Accepted: 11 July 1997     

Desulfitobacterium sp. strain PCE1, an anaerobic bacterium that can grow by reductive dechlorination of tetrachloroethene or ortho-chlorinated phenols

A strictly anaerobic bacterium, strain PCE1, was isolated from a tetrachloroethene-dechlorinating enrichment culture. Cells of the bacterium were motile curved rods, with approximately four lateral flagella. They possessed a gram-positive type of cell wall and contained cytochrome c. Optimum growth occurred at pH 7.2–7.8 and 34–38° C. The organism grew with l-lactate, pyruvate, butyrate, formate, succinate, or ethanol as electron donors, using either tetrachloroethene, 2-chlorophenol, 2,4,6-trichlorophenol, 3-chloro-4-hydroxy-phenylacetate, sulfite, thiosulfate, or fumarate as electron acceptors. Strain PCE1 also grew fermentatively with pyruvate as the sole substrate. l-Lactate and pyruvate were oxidized to acetate. Tetrachloroethene was reductively dechlorinated to trichloroethene and small amounts (< 5%) of cis-1,2-dichloroethene and trans-1,2-dichloroethene. Chlorinated phenolic compounds were dechlorinated specifically at the ortho-position. On the basis of 16S rRNA sequence analysis, the organism was identified as a species within the genus Desulfitobacterium, which until now only contained the chlorophenol-dechlorinating bacterium, Desulfitobacterium dehalogenans. Received: 31 August 1995 / Accepted: 14 November 1995     

Reductive dechlorination of chlorinated ethene DNAPLs by a culture enriched from contaminated groundwater

A microbial culture enriched from a trichloroethene-contaminated groundwater aquifer reductively dechlorinated trichloroethene (TCE) and tetrachloroethene (PCE) to ethene. Initial PCE dechlorination rate studies indicated a first-order dependence with respect to substrate at low PCE concentrations, and a zero-order dependence at high concentrations. Studies of TCE and vinyl chloride (VC) dechlorination indicated a first-order dependence at all substrate concentrations. VC had little or no effect on the initial rate of TCE dechlorination. With subsaturating concentrations of chlorinated ethenes, nearly stoichiometric amounts of the toxic intermediate vinyl chloride accumulated prior to its dechlorination to ethene. In contrast, under saturating conditions, in which a dense, nonaqueous-phase liquid existed in equilibrium with the aqueous phase, the chlorinated ethene was dechlorinated to ethene, at a rapid rate, with the accumulation of relatively small amounts of chlorinated intermediates.     

Continuous dechlorination of tetrachloroethene in an upflow anaerobic sludge blanket reactor

Influences of hydraulic retention time (HRT) on dechlorination of tetrachloroethene (PCE) were investigated in an upflow anaerobic sludge blanket (UASB) reactor inoculated with anaerobic granular sludge non-pre-exposed to chlorinated compounds. PCE was introduced into the reactor at a loading rate of 3 mg/l d. PCE removal increased from 51 +/- 5% to 87 +/- 3% when HRT increased from 1 to 4 d, corresponding to an increase in the PCE biotransformation rate from 10.5 +/- 2.3 to 21.3 +/- 3.7 mumol/d. A higher ethene production rate, 0.9 +/- 0.2 mumol/d, was attained without accumulation of dichloroethenes at the HRT of 4 d. Dehalococcoides-like species were detected in sludge granules by fluorescence in situ hybridization, with signal strength in proportion to the extent of PCE dechlorination.     

Structure analysis and performance of a microbial community from a contaminated aquifer involved in the complete reductive dechlorination of 1,1,2,2-tetrachloroethane to ethene

An anaerobic microcosm set up with aquifer material from a 1,1,2,2-tetrachloroethane (TeCA) contaminated site and amended with butyrate showed a complete TeCA dechlorination to ethene. A structure analysis of the microbial community was performed by fluorescence in situ hybridization (FISH) with already available and on purpose designed probes from sequences retrieved through 16S rDNA clone library construction. FISH was chosen as identification tool to evaluate in situ whether the retrieved sequences belong to primary bacteria responsible for the biodegradative reactions. FISH probes identified up to 80% of total bacteria and revealed the absence or the marginal presence of known TeCA degraders and the abundance of two well-known H(2)-utilizing halorespiring bacteria, Sulfurospirillum (32.4 +/- 8.6% of total bacteria) and Dehalococcoides spp. (14.8 +/- 2.8), thereby providing a strong indication of their involvement in the dechlorination processes. These results were supported by the kinetic and thermodynamic analysis which provided indications that hydrogen was the actual electron donor for TeCA dechlorination. The specific probes, developed in this study, for known dechlorinators (i.e., Geobacter, Dehalobacter, and Sulfurospirillum species) represent a valuable tool for any future in situ bioremediation study as well as a quick and specific investigation tool for tracking their distribution in the field.