Temperature determines the pattern of anaerobic microbial dechlorination of Aroclor 1260 primed by 2,3,4,6-tetrachlorobiphenyl in Woods Pond sediment.

Reductive dechlorination of the Aroclor 1260 residue in Woods Pond (Lenox, Mass.) sediment samples was investigated for a year at incubation temperatures from 4 to 66 degrees C. Sediment slurries were incubated anaerobically with and without 2,3,4,6-tetrachlorobiphenyl (2346-CB; 350 microM) as a primer for dechlorination of the Aroclor 1260 residue. Dechlorination of the Aroclor residue occurred only in live samples primed with 2346-CB and only at 8 to 34 degrees C and 50 to 60 degrees C. The extent and pattern of polychlorinated biphenyl (PCB) dechlorination were temperature dependent. At 8 to 34 degrees C, the dechlorination resulted in 28 to 65% decreases of the hexathrough nonachlorobiphenyls and corresponding increases in the tri- and tetrachlorobiphenyls. At 12 to 30 degrees C, 30 to 40% of the hexa- through nonachlorobiphenyls were dechlorinated in just 3 months. The optimal temperature for overall chlorine removal was 20 to 27 degrees C. We observed four different microbial dechlorination processes with different but partially overlapping temperature ranges, i.e., Process N (flanked meta dechlorination) at 8 to 30 degrees C, Process P (flanked para dechlorination) at 12 to 34 degrees C, Process LP (unflanked para dechlorination) at 18 to 30 degrees C, and Process T (a very restricted meta dechlorination of specific hepta- and octachlorobiphenyls) at 50 to 60 degrees C. These temperature ranges should aid in the development of strategies for the enrichment and isolation of the microorganisms responsible for each dechlorination process. The incubation temperature determined the relative dominance of the four PCB dechlorination processes and the extent and products of dechlorination. Hence, understanding the effects of temperature on PCB dechlorination at contaminated sites should assist in predicting the environmental fate of PCBs or planning bioremediation strategies at those sites.     

Microbial Reductive Dechlorination of Aroclor 1260 in Anaerobic Slurries of Estuarine Sediments

Reductive dechlorination of Aroclor 1260 was investigated in anaerobic slurries of estuarine sediments from Baltimore Harbor (Baltimore, Md.). The sediment slurries were amended with 800 ppm Aroclor 1260 with and without the addition of 350 μM 2,3,4,5-tetrachlorobiphenyl (2,3,4,5-CB) or 2,3,5,6-tetrachlorobiphenyl (2,3,5,6-CB) and incubated in triplicate at 30°C under methanogenic conditions in an artificial estuarine medium. After 6 months, extensive meta dechlorination and moderate ortho dechlorination of Aroclor 1260 occurred in all incubated cultures except for sterilized controls. Overall, total chlorines per biphenyl decreased by up to 34%. meta chlorines per biphenyl decreased by 65, 55, and 45% and ortho chlorines declined by 18, 12, and 9%, respectively, when 2,3,4,5-CB, 2,3,5,6-CB, or no additional congener was supplied. This is the first confirmed report of microbial ortho dechlorination of a commercial polychlorinated biphenyl mixture. In addition, compared with incubated cultures supplied with Aroclor 1260 alone, the dechlorination of Aroclor 1260 plus 2,3,4,5-CB or 2,3,5,6-CB occurred with shorter lag times (31 to 60 days versus 90 days) and was more extensive, indicating that the addition of a single congener stimulated the dechlorination of Aroclor 1260.     

Brominated Biphenyls Prime Extensive Microbial Reductive Dehalogenation of Aroclor 1260 in Housatonic River Sediment

The upper Housatonic River and Woods Pond (Lenox, Mass.), a shallow impoundment on the river, are contaminated with polychlorinated biphenyls (PCBs), the residue of partially dechlorinated Aroclor 1260. Certain PCB congeners have the ability to activate or “prime” anaerobic microorganisms in Woods Pond sediment to reductively dehalogenate the Aroclor 1260 residue. We proposed that brominated biphenyls might have the same effect and tested the priming activities of 14 mono-, di-, and tribrominated biphenyls (350 μM) in anaerobic microcosms of sediment from Woods Pond. All of the brominated biphenyls were completely dehalogenated to biphenyl, and 13 of them primed PCB dechlorination. Measured in terms of chlorine removal and decrease in the proportion of hexa- through nonachlorobiphenyls, the microbial PCB dechlorination primed by several brominated biphenyls was nearly twice as effective as that primed by chlorinated biphenyls. Congeners containing a meta bromine primed Dechlorination Process N (flanked meta dechlorination), and congeners containing an unflanked para bromine primed Dechlorination Process P (flanked para dechlorination). Two ortho-substituted congeners, 2-bromobiphenyl and 2,6-dibromobiphenyl (2-BB and 26-BB), also primed Process N dechlorination. The most effective primers were 26-BB, 245-BB, 25-3-BB, and 25-4-BB. The microbial dechlorination primed by 26-BB converted ~75% of the hexa- through nonachlorobiphenyls to tri- and tetrachlorobiphenyls in 100 days and removed ~75% of the PCBs that are most persistent in humans. These results represent a major step toward identifying an effective method for accelerating PCB dechlorination in situ. The challenge now is to identify naturally occurring compounds that are safe and effective primers.     

Reductive dechlorination of PCB-contaminated raisin river sediments by anaerobic microbial granules

A polychlorinated biphenyl (PCB)-dechlorinating anaerobic microbial consortium, developed in a granular form, demonstrated extensive dechlorination of PCBs present in Raisin River sediments at room (20 degrees to 22 degrees C) and at a relatively low (12 degrees C) temperature. Highly chlorinated PCB congeners were dechlorinated and less chlorinated compounds were produced. The homolog comparison showed that tri-, tetra-, penta-, hexa-, and heptachlorobiphenyl compounds decreased significantly, and mono- and dichlorobiphenyl compounds increased. After 32 weeks of incubation at 12 degrees C, the predominant less chlorinated products included 2-, 4-, 2-2/26-, 24-, 2-4-, 24-2-, 26-2-, and 26-4-CB. Among these, 24- and 24-2-CB did not accumulate at room temperature, suggesting a further dechlorination of these congeners. Predominantly meta dechlorination (i.e., pattern M) was catalyzed by the microbial consortium in the granules. Dechlorination in the control studies without granules was not extensive. This study is the first demonstration of enhanced reductive dechlorination of sediment PCBs by an exogenous anaerobic microbial consortium. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 182-190, 1997.     

Reductive dechlorination of hexachlorobenzene to tri- and dichlorobenzenes in anaerobic sewage sludge

Hexachlorobenzene was dechlorinated to tri- and dichlorobenzenes in anaerobic sewage sludge. The complete biotransformation of 190 microM hexachlorobenzene (approximately 50 ppm) occurred within 3 weeks. The calculated rate of hexachlorobenzene dechlorination was 13.6 mumol liter-1 day-1. Hexachlorobenzene was dechlorinated via two routes, both involving the sequential removal of chlorine from the aromatic ring. The major route was hexachlorobenzene----pentachlorobenzene----1,2,3,5-tetrachlorobenzene--- -1,3,5- trichlorobenzene. Greater than 90% of the added hexachlorobenzene was recovered as 1,3,5-trichlorobenzene, and there was no evidence for further dechlorination of 1,3,5-trichlorobenzene. The minor route was hexachlorobenzene----pentachlorobenzene----1,2,4,5-tetrachlorobenzene--- -1,2,4- trichlorobenzene----dichlorobenzenes. These results extend reductive dechlorination to poorly water soluble aromatic hydrocarbons which could potentially include other important environmental pollutants like polychlorinated biphenyls.     

Reductive dechlorination of hexachlorobenzene to tri- and dichlorobenzenes in anaerobic sewage sludge.

Hexachlorobenzene was dechlorinated to tri- and dichlorobenzenes in anaerobic sewage sludge. The complete biotransformation of 190 microM hexachlorobenzene (approximately 50 ppm) occurred within 3 weeks. The calculated rate of hexachlorobenzene dechlorination was 13.6 mumol liter-1 day-1. Hexachlorobenzene was dechlorinated via two routes, both involving the sequential removal of chlorine from the aromatic ring. The major route was hexachlorobenzene----pentachlorobenzene----1,2,3,5-tetrachlorobenzene--- -1,3,5- trichlorobenzene. Greater than 90% of the added hexachlorobenzene was recovered as 1,3,5-trichlorobenzene, and there was no evidence for further dechlorination of 1,3,5-trichlorobenzene. The minor route was hexachlorobenzene----pentachlorobenzene----1,2,4,5-tetrachlorobenzene--- -1,2,4- trichlorobenzene----dichlorobenzenes. These results extend reductive dechlorination to poorly water soluble aromatic hydrocarbons which could potentially include other important environmental pollutants like polychlorinated biphenyls.     

Reductive dechlorination of hexachlorocyclohexane (HCH) isomers in soil under anaerobic conditions

The biological anaerobic reductive dechlorination of beta-hexachlorocyclohexane under methanogenic conditions was tested in a number of contaminated soil samples from two locations in the Netherlands. Soils from a heavily polluted location showed rapid dechlorination of beta-hexachlorocyclohexane to benzene and chlorobenzene with lactate as electron donor. Soils from an adjacent slightly polluted location did not show substantial dechlorination of beta-hexachlorocyclohexane within 4 months. A heavily polluted sample was selected to optimise the dechlorination. All tested hexachlorocyclohexane isomers (alpha-, beta-, gamma-, and delta-), either added separately or simultaneously, were dechlorinated in this soil sample. The most rapid dechlorination was observed at a temperature of 30 degrees C. Dechlorination of beta-hexachlorocyclohexane was observed with acetate, propionate, lactate, methanol, H2, yeast extract and landfill leachate as electron donors. In a soil percolation column, packed with a selected heavily polluted soil sample, the presence of 10 mM sulphate in the influent led to simultaneous dechlorination of beta-hexachlorocyclohexane and sulphate reduction. When the column was fed with 10 mM nitrate instead of sulphate, dechlorination ceased immediately. After omitting nitrate from the influent, dechlorination activity recovered in about 1 month. Also in a separate column, the addition of nitrate from the start of the experiment did not result in dechlorination of beta-HCH. The significance of these experiments for in situ bioremediation of polluted soils is discussed.     

Reductive dechlorination of chlorophenols in slurries of low-organic-carbon marine sediments and subsurface soils

The reductive dechlorination of 2,4- and 3,4-dichlorophenol (DCP) was studied in slurries of marine sediments and subsurface soils with dissolved organic carbon concentrations less than 1 ppm. Dechlorination was markedly greater in marine sediment slurries than in subsoil slurries, although similar products were observed in each case. From 25% to 98% of the 2,4- and 3,4-DCP (6.5 μm/l) added to most marine slurries was converted to 4- and 3-chlorophenol (CP) respectively, within 30 weeks. In contrast 2,4-DCP was dechlorinated to 4-CP (>90%) in only 1 of 24 replicate subsoil slurries after 32 weeks of incubation. Dechlorination was observed within 2 weeks when yeast extract was added to subsoil slurries; yeast extract additions also stimulated dechlorination in marine sediments but to a lesser extent. The intermediate monochlorophenol products did not persist in marine slurries but did persist in the subsoil slurries. It was concluded that the total organic carbon at a site is not always a good predictor of the site's ability to support dechlorination activity. Received: 3 December 1996 / Received revision: 28 February 1997 / Accepted: 7 March 1997     

Reductive dechlorination of Tri- and tetrachloroethylenes depends on transition from aerobic to anaerobic conditions

Aerobic enrichment cultures from contaminated groundwaters dechlorinated trichloroethylene (TCE) (14.6 mg/liter; 111 mumol/liter) and tetrachloroethylene (PCE) (16.2 mg/liter; 98 mumol/liter) reductively within 4 days after the transition from aerobic to anaerobic conditions. The transformation products were equimolar amounts of cis-1,2-dichloroethylene and traces of 1,1-dichloroethylene. No other chlorinated product and no methane were detected. The change was accompanied by the release of sulfide, which caused a decrease in the redox potential from 0 to -150 mV. In sterile control experiments, sulfide led to the abiotic formation of traces of 1,1-dichloroethylene without cis-1,2-dichloroethylene production. The reductive dechlorination of PCE via TCE depended on these specific transition conditions after consumption of the electron acceptor oxygen or nitrate. Repeated feeding of TCE or PCE to cultures after the change to anaerobic conditions yielded no further dechlorination. Only aerobic subcultures with an air/liquid ratio of 1:4 maintained dechlorination activities; anaerobic subcultures showed no transformation. Bacteria from noncontaminated sites showed no reduction under the same conditions.     

Microbial Reductive Dechlorination of Aroclor 1260 in Baltimore Harbor Sediment Microcosms Is Catalyzed by Three Phylotypes within the Phylum Chloroflexi

The specific dechlorination pathways for Aroclor 1260 were determined in Baltimore Harbor sediment microcosms developed with the 11 most predominant congeners from this commercial mixture and their resulting dechlorination intermediates. Most of the polychlorinated biphenyl (PCB) congeners were dechlorinated in the meta position, and the major products were tetrachlorobiphenyls with unflanked chlorines. Using PCR primers specific for the 16S rRNA genes of known PCB-dehalogenating bacteria, we detected three phylotypes within the microbial community that had the capability to dechlorinate PCB congeners present in Aroclor 1260 and identified their selective activities. Phylotype DEH10, which has a high level of sequence identity to Dehalococcoides spp., removed the double-flanked chlorine in 234-substituted congeners and exhibited a preference for para-flanked meta-chlorines when no double-flanked chlorines were available. Phylotype SF1 had similarity to the o-17/DF-1 group of PCB-dechlorinating bacteria. Phylotype SF1 dechlorinated all of the 2345-substituted congeners, mostly in the double-flanked meta position and 2356-, 236-, and 235-substituted congeners in the ortho-flanked meta position, with a few exceptions. A phylotype with 100% sequence identity to PCB-dechlorinating bacterium o-17 was responsible for an ortho and a double-flanked meta dechlorination reaction. Most of the dechlorination pathways supported the growth of all three phylotypes based on competitive PCR enumeration assays, which indicates that PCB-impacted environments have the potential to sustain populations of these PCB-dechlorinating microorganisms. The results demonstrate that the variation in dechlorination patterns of congener mixtures typically observed at different PCB impacted sites can potentially be mediated by the synergistic activities of relatively few dechlorinating species.     

Reductive dechlorination of Tri- and tetrachloroethylenes depends on transition from aerobic to anaerobic conditions.

Aerobic enrichment cultures from contaminated groundwaters dechlorinated trichloroethylene (TCE) (14.6 mg/liter; 111 mumol/liter) and tetrachloroethylene (PCE) (16.2 mg/liter; 98 mumol/liter) reductively within 4 days after the transition from aerobic to anaerobic conditions. The transformation products were equimolar amounts of cis-1,2-dichloroethylene and traces of 1,1-dichloroethylene. No other chlorinated product and no methane were detected. The change was accompanied by the release of sulfide, which caused a decrease in the redox potential from 0 to -150 mV. In sterile control experiments, sulfide led to the abiotic formation of traces of 1,1-dichloroethylene without cis-1,2-dichloroethylene production. The reductive dechlorination of PCE via TCE depended on these specific transition conditions after consumption of the electron acceptor oxygen or nitrate. Repeated feeding of TCE or PCE to cultures after the change to anaerobic conditions yielded no further dechlorination. Only aerobic subcultures with an air/liquid ratio of 1:4 maintained dechlorination activities; anaerobic subcultures showed no transformation. Bacteria from noncontaminated sites showed no reduction under the same conditions.     

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%).     

Reductive dechlorination of DDT by haem proteins.

DDT1 is converted to DDD by reduced myoglobin (rapidly), cytochrome c oxidase, and a haem-containing undecapeptide derived from cytochrome c. Cytochrome c itself is inactive. This demonstrates that an accessible haem site is necessary for the reaction. Spectrophotometric evidence is presented for an interaction between DDT and the undecapeptide. These results cast light on one of the biological pathways for the breakdown of DDT.     

Reductive dechlorination of all trichloro- and dichlorobenzene isomers

Abstract All three isomers of trichlorobenzene were reductively dechlorinated to monochlorobenzene via dichlorobenzenes in anaerobic sediment columns. The dechlorination was specific: 1,2,3- and 1,3,5-trichlorobenzene were solely transformed to 1,3-dichlorobenzene, while 1,4-dichlorobenzene was the only product of 1,2,4-trichlorobenzene transformation. Microorganisms were responsible for the observed transformations. Since monochlorobenzene and dichlorobenzene are mineralized by bacteria in the presence of oxygen, the process of reductive dechlorination may be an important initial step to obtain complete mineralization of otherwise recalcitrant trichlorobenzenes. This is especially true for the 1,3,5-isomer, which seems to resist biodegradation in oxic environments.     

零价金属降解多氯联苯(PCBs)

多氯联苯(polychlorinated biphenyls,简称PCBs)是一类对环境有不利影响的有毒有机物,它在环境中广泛而大量分布。许多科学家都在致力于有效处理PCBs污染介质(包括水、油、沉积物和土壤)的修复技术的研究。本文综述了国内外在零价金属还原脱氯降解PCBs领域的研究状况。在高温等特殊条件下或有钯、铂、镍和铜等催化剂存在的条件下,零价金属能有效促进PCBs还原脱氯。讨论了零价铁还原脱氯的3个可能的途径:金属直接反应,将零价铁表面的电子转移到有机氯化物使之脱氯;铁腐蚀的直接产物Fe2 具有还原能力,它可使得一部分氯代烃脱氯;铁反应产生的氢气可使有机氯化物还原。评述了零价金属还原脱氯PCBs具有有效、廉价和易得的特点。展望了零价金属还原脱氯降解PCBs研究领域的发展前景。     

Phylogenetically Distinct Bacteria Involve Extensive Dechlorination of Aroclor 1260 in Sediment-Free Cultures

Microbial reductive dechlorination of the persistent polychlorinated biphenyls (PCBs) is attracting much attention in cleanup of the contaminated environment. Nevertheless, most PCB dechlorinating cultures require presence of sediment or sediment substitutes to maintain their dechlorination activities which hinders subsequent bacterial enrichment and isolation processes. The information on enriching sediment-free PCB dechlorinating cultures is still limited. In this study, 18 microcosms established with soils and sediments were screened for their dechlorination activities on a PCB mixture – Aroclor 1260. After one year of incubation, 10 out of 18 microcosms showed significant PCB dechlorination with distinct dechlorination patterns (e.g., Process H, N and T classified based on profiles of PCB congeners loss and new congeners formation). Through serial transfers in defined medium, six sediment-free PCB dechlorinating cultures (i.e., CW-4, CG-1, CG-3, CG-4, CG-5 and SG-1) were obtained without amending any sediment or sediment-substitutes. PCB dechlorination Process H was the most frequently observed dechlorination pattern, which was found in four sediment-free cultures (CW-4, CG-3, CG-4 and SG-1). Sediment-free culture CG-5 showed the most extensive PCB dechlorination among the six cultures, which was mediated by Process N, resulting in the accumulation of penta- (e.g., 236-24-CB) and tetra-chlorobiphenyls (tetra-CBs) (e.g., 24-24-CB, 24-25-CB, 24-26-CB and 25-26-CB) via dechlorinating 30.44% hepta-CBs and 59.12% hexa-CBs after three months of incubation. For culture CG-1, dechlorinators mainly attacked double flanked meta-chlorines and partially ortho-chlorines, which might represent a novel dechlorination pattern. Phylogenetic analysis showed distinct affiliation of PCB dechlorinators in the microcosms, including Dehalogenimonas and Dehalococcoides species. This study broadens our knowledge in microbial reductive dechlorination of PCBs, and provides essential information for culturing and stimulating PCB dechlorinators for in situ bioremediation applications.     

Changes in the microbial community during repeated anaerobic microbial dechlorination of pentachlorophenol

Pentachlorophenol (PCP) has been widely used as a pesticide in paddy fields and has imposed negative ecological effect on agricultural soil systems, which are in typically anaerobic conditions. In this study, we investigated the effect of repeated additions of PCP to paddy soil on the microbial communities under anoxic conditions. Acetate was added as the carbon source to induce and accelerate cycles of the PCP degradation. A maximum degradation rate occurred at the 11th cycle, which completely transformed 32.3 μM (8.6 mg L^?1) PCP in 5 days. Illumina high throughput sequencing of 16S rRNA gene was used to profile the diversity and abundance of microbial communities at each interval and the results showed that the phyla of Bacteroidates, Firmicutes, Proteobacteria, and Euryarchaeota had a dominant presence in the PCP-dechlorinating cultures. Methanosarcina, Syntrophobotulus, Anaeromusa, Zoogloea, Treponema, W22 (family of Cloacamonaceae), and unclassified Cloacamonales were found to be the dominant genera during PCP dechlorination with acetate. The microbial community structure became relatively stable as cycles increased. Treponema, W22, and unclassified Cloacamonales were firstly observed to be associated with PCP dechlorination in the present study. Methanosarcina that have been isolated or identified in PCP dechlorination cultures previously was apparently enriched in the PCP dechlorination cultures. Additionally, the iron-cycling bacteria Syntrophobotulus, Anaeromusa, and Zoogloea were enriched in the PCP dechlorination cultures indicated they were likely to play an important role in PCP dechlorination. These findings increase our understanding for the microbial and geochemical interactions inherent in the transformation of organic contaminants from iron rich soil, and further extend our knowledge of the PCP-transforming microbial communities in anaerobic soil conditions.     

Reductive dechlorination of halogenated phenols by a sulfate-reducing consortium

A sulfidogenic consortium enriched from an estuarine sediment utilized 4-chlorophenol as a sole source of carbon and energy. Reductive dechlorination as the initial step in chlorophenol degradation by the sulfate-reducing consortium was confirmed with the use of chloro-fluorophenols. Both 4-chloro-2-fluorophenol and 4-chloro-3-fluorophenol were dechlorinated, resulting in stoichiometric accumulation of 2-fluorophenol and 3-fluorophenol, respectively. The fluorophenols were not degraded further. Furthermore, phenol was detected as a transient intermediate during degradation of 4-chlorophenol in the presence of 3-fluorophenol. Reductive dechlorination was inhibited by molybdate and did not occur in the absence of sulfate. These results indicate that 4-chlorophenol is reductively dechlorinated to phenol under sulfate-reducing conditions and mineralization of the phenol ring to CO₂ is coupled to sulfate reduction.