Reductive dechlorination of dichlorophenols by nonadapted and adapted microbial communities in pond sediments

Fresh and dichlorophenol (DCP)-adapted sediments from two ponds near Athens, Georgia exhibited distinctly different dechlorinating activities. These differences centered on the relative rates of reductive dehlorination in both fresh and adapted sediments and on the substrate specificity of the adapted sediments. Fresh Cherokee Trailer Park Pond sediment dechlorinated 2,3-, 2,4-, and 2,6-DCP to monochlorophenols at a faster rate and after a shorter lag period than fresh Bolton's Pond sediment. Lag periods were not observed in either Cherokee or Bolton's sediments that had been adapted to dechlorinate either 2,3-, 2,4-or 2,6-DCP. Adapted Cherokee sediments exhibited faster dechlorinating rates and a broader substrate specificity than the adapted Bolton's sediments. The broad substrate specificity of each of the adapted Cherokee sediments contrasted sharply with the narrow specificity of the 2,6-DCP-adapted Bolton's sediment. The preference for reductive dechlorination wasortho>meta orpara in sediments from both ponds.     

Reductive dechlorination of weathered Aroclor 1260 during anaerobic biotreatment of Arctic soils

We investigated the microbial reductive dechlorination of both weathered (aged) and nonweathered (freshly added) Aroclor 1260 in aerobic soil from Resolution Island, Nunavut, Canada. Initial polychlorinated biphenyl (PCB) concentrations were 106 and 100 ppm, respectively. The aerobic soil samples were inoculated with anaerobic sediment, incubated at 30 degrees C until methanogenic, inoculated with a dechlorinating enrichment culture, and incubated a further 8 weeks. The average number of chlorine substituents per biphenyl molecule was biologically reduced from 6.6 to 5.1 and from 6.2 to 4.5 for weathered and nonweathered Aroclor 1260, respectively. Removal of hexa- and heptachlorobiphenyls (CBs), the major homolog groups present, was significantly greater for nonweathered than for weathered Aroclor 1260. Formation of dechlorination products, primarily 2,2',4,4'- and 2,2',4,6'-tetraCBs, was also significantly greater for nonweathered than for weathered Aroclor 1260. We additionally compared the dechlorination at 21 degrees C of weathered Aroclor 1260 in soils from Resolution Island and Saglek, Labrador, Canada. The average number of chlorine substituents per biphenyl molecule was biologically reduced from 6.7 to 5.1 and from 6.5 to 4.6, respectively. This study demonstrated the potential for bioremediation of aerobic soil contaminated with Aroclor 1260 and showed that weathering may limit such treatment to an extent variable among different soils.     

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.     

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.     

Comparison of anaerobic microbial communities from Estuarine sediments amended with halogenated compounds to enhance dechlorination of 1,2,3,4-tetrachlorodibenzo-p-dioxin

A suite of experiments were conducted to ascertain whether dehalogenation of a model dioxin compound could be stimulated in marine sediments by supplementation with halogenated analogues to enrich for dehalogenating bacteria and if growth by members of the Chloroflexi-like group was associated with dioxin removal. Five halogenated compounds (tetrachlorobenzene, tetrachloroanisole, tetrachlorophenol, tetrachlorobenzoic acid and trichloroacetophenone) were added with 1,2,3,4-tetrachlorodibenzo-p-dioxin (TeCDD) to estuarine sediments from four sites in San Diego Bay and the coast of southern New Jersey to test for dioxin dehalogenation. Most of the halogenated additives were found to stimulate dechlorination of the model dioxin. Molecular analysis of the bacterial population using 16S rRNA and reductive dehalogenase genes indicated that distinct microbial populations were enriched with each halogenated co-amendment. Additionally, Chloroflexi-like ribosomal genes associated with dehalogenation were detected. For example, quantitative real-time PCR analysis of 16S rRNA and reductive dehalogenase gene copy number in the microcosms showed a positive correlation with 1,2,3,4-TeCDD reductive dechlorination in coastal sediments amended with different halogenated additives. These results suggest that specific Chloroflexi-like microorganisms related to Dehalococcoides are involved in 1,2,3,4-TeCDD reductive dechlorination.     

Aerobic and anaerobic microbial activity in deep subsurface sediments from the savannah river plant

Methanogenesis, sulfate reduction, and rates of carbon mineralization were determined for samples derived at different depths from four cores drilled at the Savannah River Plant, Aiken South Carolina. Three‐gram subsamples of the sediments were dispensed to 10‐mL serum bottles under 5% H₂/95% N₂ and amended with 0.5 mL degassed distilled water with or without the following solutes: formate plus acetate, bicarbonate, lactate, and radiolabeled sulfate, glucose, and Índole. After incubating 1 to 5 days, the sediments were assayed for methane, H₂, ³⁵S, and ^I4CO₂. No methanogenesis was detected at any depth in any core and sulfate was rarely reduced. Evolution of ¹⁴CO₂ from glucose and indole was detected in sediments as deep as 262 and 259 m, respectively. At some depths the ¹⁴CO₂ evolution rate was comparable to that of surface soils; however, at other depths no ¹⁴CO₂ evolution could be detected. Injection of sterile air into anaerobic incubations increased rates of carbon mineralization at all depths that had demonstrated anaerobic activity and stimulated mineralization activity in sediments that were inactive anaerobically, suggesting a predominance of aerobic metabolism. Increasing the concentration of added glucose and indole often increased the resulting rates of ¹⁴CO₂ evolved from these substrates. Our data indicate that both aerobic and anaerobic microorganisms are present and metabolically active in samples from deep subsurface environments.     

Kinetics of the sequential dechlorination of 2,4,6-trichlorophenol by an anaerobic microbial population

Summary A mathematical model was developed to describe the sequential dechlorination of 2,4,6-trichlorophenol to 2,4-dichlorophenol, 4-chlorophenol and phenol. Each compound was assumed to be degraded according a Michaelis-Menten expression. Experimental data were used to obtain the model kinetic constants and to test its validity. Good agreement between the model predictions and the experimental data was obtained.     

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 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.     

Enhanced dechlorination of 2,4,6-trichlorophenol by anaerobic microbial populations in the presence of ethanol

Summary A consortium of anaerobic microorganisms was grown on acetate, ethanol, glucose or methanol and dechlorinated 50 umol 2,4,6-trichlorophenol, through 2,4-dichlorophenol, to 4-chlorophenol. The highest rate of dechlorination of 2,4,6-trichlorophenol was observed when ethanol was used as a growth substrate.     

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。     

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 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.     

Presence of anaerobic bacteroides in aerobically grown microbial granules

Microbial granules were grown in a column-type sequential aerobic sludge blanket reactor inoculated with activated sludge flocs taken from a wastewater treatment plant and containing a medium with glucose as the main carbon source. The reactor selected for granules that could settle rapidly by employing a short settling time of 2 min. Matured granules with diameters between 2 and 3 mm were examined for anaerobic bacteria as their presence can signal the onset of diffusion limitation problems that can potentially diminish granule stability due to the bacterial production of fermentation gases and organic acids under anaerobic conditions. To detect the anaerobes in the granules, clones were constructed from 16S rRNA PCR amplicons. Two sequence types associated with a strict anaerobe Bacteroides spp. were identified from these clones. Fluorescence in situ hybridization (FISH) followed by confocal laser scanning microscopy (CLSM) demonstrated that cells of Bacteroides spp. were concentrated at a depth of approximately 800 mm below the surface of the granule. Cell enumeration using flow cytometry showed that the percentage of labeled cells of Bacteroides spp. compared to total bacterial cells in the granules was 0.56%. This is the first study to use a suite of culture-independent techniques to report the presence of a defined species of anaerobic bacteria in aerobically grown microbial granules.     

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.