Anaerobic dechlorination of polychlorobiphenyls (Aroclor 1242) by pasteurized and ethanol-treated microorganisms from sediments

Levels of Polychlorinated Biphenyls in Plastic Resin Pellets from Six Beaches on the Accra-Tema Coastline, Ghana

BACKGROUND

Polychlorinated biphenyls (PCBs) are organic compounds, known to be carcinogenic and banned by the Stockholm Convention. PCBs are hydrophobic substances able to accumulate in organic materials, including plastic pellets. Plastic resin pellets are industrial raw materials that are remolded finished products for industrial and domestic use, commonly used for packaging. Plastic resin pellets were chosen as the medium for monitoring hydrophobic contaminants because they are able to adsorb PCB contaminants. Pellets can be unintentionally washed into the ocean where hydrophobic contaminants such as PCBs are also deposited.

OBJECTIVES

We aimed to identify PCB congeners and quantify PCB pollution levels in the marine environment using resin plastic pellets collected from six beaches along the Accra-Tema coastline in Ghana.

METHODS

Plastic resin pellets (5 g) were extracted with 200 mL of n-hexane for 16 hours by Soxhlet extraction. Concentrations of PCBs from the extracts were determined using gas chromatography with an electron capture detector.

RESULTS

The individual PCB congeners detected were PCB 28, 52, 101, 105, 138, 153, 156 and 180. PCB 28 was detected at all six beaches, with a total concentration of 43.5 ng/g pellet (mean/beach 7.25 +/- 2.47 ng/g pellet; CV = 34%), while PCB 138 was only detected on one beach (Castle Beach) at a total concentration of 0.8 ng/g pellet. The concentration of PCBs ranged from 7.4 ng/g (Sunset Beach) to 47.5 ng/g (Castle Beach) (mean 16.4±15.4 ng/g per beach; CV=94%).

DISCUSSION

PCB concentrations at Castle Beach have been studied previously, showing an increase from 39 ng/g to 47.5 ng/g, whereas levels decreased significantly from 28 ng/g to 14.2 ng/g in Sakumono Beach over the span of three years.

CONCLUSIONS

The concentrations of four detected PCB congeners (28, 52, 101 and 156) were significantly higher than the World Health Organization (WHO) allowable daily intake of 6 ng/g food per day for PCBs. A more efficient industrial and domestic waste disposal system is advocated for Ghana.

Indirect Evidence Link PCB Dehalogenation with Geobacteraceae in Anaerobic Sediment-Free Microcosms

Although polychlorinated biphenyls (PCBs) production was brought to a halt 30 years ago, recalcitrance to degradation makes them a major environmental pollutant at a global scale. Previous studies confirmed that organohalide-respiring bacteria (OHRB) were capable of utilizing chlorinated congeners as electron acceptor. OHRB belonging to the Phyla Chloroflexi and Firmicutes are nowadays considered as the main PCB-dechlorinating organisms. In this study, we aimed at exploring the involvement of other taxa in PCB dechlorination using sediment-free microcosms (SFMs) and the Delor PCB mixture. High rates of congener dehalogenation (up to 96%) were attained in long-term incubations of up to 692 days. Bacterial communities were dominated by Chloroflexi, Proteobacteria, and Firmicutes, among strictly simplified community structures composed of 12 major phyla only. In a first batch of SFMs, Dehalococcoides mccartyi closely affiliated with strains CG4 and CBDB1 was considered as the main actor associated with congener dehalogenation. Addition of 2-bromoethanesulfonate (BES), a known inhibitor of methanogenic activity in a second batch of SFMs had an adverse effect on the abundance of Dehalococcoides sp. Only two sequences affiliated to this Genus could be detected in two (out of six) BES-treated SFMs, contributing to a mere 0.04% of the communities. BES-treated SFMs showed very different community structures, especially in the contributions of organisms involved in fermentation and syntrophic activities. Indirect evidence provided by both statistical and phylogenetic analysis validated the implication of a new cluster of actors, distantly affiliated with the Family Geobacteraceae (Phylum δ-Proteobacteria), in the dehalogenation of low chlorinated PCB congeners. Members of this Family are known already for their dehalogenation capacity of chlorinated solvents. As a result, the present study widens the knowledge for the phylogenetic reservoir of indigenous PCB dechlorinating taxa.

Overview of in situ and ex situ remediation technologies for PCB-contaminated soils and sediments and obstacles for full-scale application

Polychlorinated biphenyls (PCB) are persistent organic pollutants used worldwide between the 1930s and 1980s. Although their use has been heavily restricted, PCB can be found in contaminated soils and sediments. The most frequent remediation solutions adopted are "dig and dump" and "dig and incinerate", but there are currently new methods that could be more sustainable alternatives. This paper takes a look into the remediation options available for PCB-contaminated soils and sediments, differentiating between biological, chemical, physical and thermal methods. The use of combined technologies was also reviewed. Most of them are still in an initial development stage and further research in different implementation issues is needed. There is no single technology that is the solution for PCB contamination problem. The successful remediation of a site will depend on proper selection, design and adjustment of the technology or combined technologies to the site characteristics.

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.

A case study for microbial biodegradation: anaerobic bacterial reductive dechlorination of polychlorinated biphenyls-from sediment to defined medium

The history of anaerobic microbial polychlorinated biphenyl (PCB) dechlorination is traced over 20 years using a case study of PCB dechlorination in the Housatonic River (Massachusetts) as an example. The history progresses from the characterization of the PCBs in the sediment, to cultivation in sediment microcosms, to the identification of four distinct types of PCB dechlorination, to a successful field test, to the cultivation in defined medium of the organisms responsible for extensive dechlorination of Aroclor 1260, and finally to the identification of a Dehalococcoides population that links its growth to the dechlorination of Aroclor 1260. Other PCB dechlorinators have also been identified. Two bacterial strains, o-17 and DF-1, that link their growth to the dechlorination of several PCB congeners belong to a novel clade of putative dechlorinating bacteria within the phylum Chloroflexi. Dehalococcoides ethenogenes strain 195 also dechlorinates several PCB congeners when grown on chlorinated ethenes. Evidence is mounting that Dehalococcoides and other dechlorinating Chloroflexi may play a significant role in the dechlorination of commercial PCBs in situ.

Microbial transformation and degradation of polychlorinated biphenyls

This paper reviews the potential of microorganisms to transform polychlorinated biphenyls (PCBs). In anaerobic environments, higher chlorinated biphenyls can undergo reductive dehalogenation. Meta- and para-chlorines in PCB congeners are more susceptible to dechlorination than ortho-chlorines. Anaerobes catalyzing PCB dechlorination have not been isolated in pure culture but there is strong evidence from enrichment cultures that some Dehalococcoides spp. and other microorganisms within the Chloroflexi phylum can grow by linking the oxidation of H(2) to the reductive dechlorination of PCBs. Lower chlorinated biphenyls can be co-metabolized aerobically. Some aerobes can also grow by utilizing PCB congeners containing only one or two chlorines as sole carbon/energy source. An example is the growth of Burkholderia cepacia by transformation of 4-chlorobiphenyl to chlorobenzoates. The latter compounds are susceptible to aerobic mineralization. Higher chlorinated biphenyls therefore are potentially fully biodegradable in a sequence of reductive dechlorination followed by aerobic mineralization of the lower chlorinated products.

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.

Degradation of aroclor 1242 dechlorination products in sediments by Burkholderia xenovorans LB400(ohb) and Rhodococcus sp. strain RHA1(fcb)

Burkholderia xenovorans strain LB400, which possesses the biphenyl pathway, was engineered to contain the oxygenolytic ortho dehalogenation (ohb) operon, allowing it to grow on 2-chlorobenzoate and to completely mineralize 2-chlorobiphenyl. A two-stage anaerobic/aerobic biotreatment process for Aroclor 1242-contaminated sediment was simulated, and the degradation activities and genetic stabilities of LB400(ohb) and the previously constructed strain RHA1(fcb), capable of growth on 4-chlorobenzoate, were monitored during the aerobic phase. The population dynamics of both strains were also followed by selective plating and real-time PCR, with comparable results; populations of both recombinants increased in the contaminated sediment. Inoculation at different cell densities (10(4) or 10(6) cells g(-1) sediment) did not affect the extent of polychlorinated biphenyl (PCB) biodegradation. After 30 days, PCB removal rates for high and low inoculation densities were 57% and 54%, respectively, during the aerobic phase.

The reductive dechlorination of 2,3,4,5-tetrachlorobiphenyl in three different sediment cultures: evidence for the involvement of phylogenetically similar Dehalococcoides-like bacterial populations

Anaerobic cultures capable of reductively dechlorinating 2,3,4,5-tetrachlorobiphenyl (CB) were enriched from three different sediments, one estuarine, one marine and one riverine. Two different electron donors were used in enrichments with the estuarine sediment (elemental iron or a mixture of fatty acids). The removal of doubly flanked meta and para chlorines to form 2,3,5-CB and 2,4,5-CB was observed in all cultures. Bacterial community analysis of PCR-amplified 16S rRNA gene fragments revealed different communities in these cultures, with the exception of one common population that showed a high phylogentic relatedness to Dehalococcoides species. No Dehalococcoides-like populations were ever detected in control cultures to which no PCBs were added. In addition, the dynamics of this Dehalococcoides-like population were strongly correlated with dechlorination. Subcultures of the estuarine sediment culture demonstrated that the Dehalococcoides-like population disappeared when dechlorination was inhibited with 2-bromoethanesulfonate or when 2,3,4,5-CB had been consumed. These results provide evidence that Dehalococcoides-like populations were involved in the removal of doubly flanked chlorines from 2,3,4,5-CB. Furthermore, the successful enrichment of these populations from geographically distant and geochemically distinct environments indicates the widespread presence of these PCB-dechlorinating, Dehalococcoides-like organisms.

Regulation of anaerobic dehalorespiration by the transcriptional activator CprK

Desulfomonile, Desulfitobacterium, and Dehalobacter are anaerobic microbes that can derive energy from the reductive dehalogenation of chlorinated organic compounds, many of which are environmental pollutants. There is very little information about how anaerobic dehalorespiration is regulated. An open reading frame within the Desulfitobacterium dehalogenans chlorophenol reductase (cpr) gene cluster (cprK) was proposed to be a transcriptional regulatory protein (Smidt, H., van Leest, M., van der Oost, J., and deVos, W. M. (2000) J. Bacteriol. 182, 5683-5691). We have cloned, actively overexpressed in Escherichia coli, and purified to homogeneity the D. dehalogenans CprK. The results of electrophoretic mobility shift assays, DNA footprinting studies, and promoter-lac fusion experiments indicate that CprK is a transcriptional activator of the cpr gene cluster. CprK binds 3-chloro-4-hydroxyphenylacetate (CHPA) with high affinity (K(d) = 3.5 mum, determined by isothermal titration calorimetry), which promotes its specific interaction with a DNA sequence (TTAAT-N4-ACTAA) located upstream of the -35 and -10 promoter regions of several cpr genes and activates transcription of these genes. Binding to the upstream "box" sequence increases the affinity of CprK for CHPA by approximately 10-fold (K(d) = 0.4 mum, determined by electrophoretic mobility shift assays). Chlorophenylacetate, which lacks the ortho-hydroxy group, and hydroxyphenylacetate, lacking the chlorine group, do not activate transcription or promote DNA binding, even at millimolar concentrations, at least 1000-fold higher than the K(d) value for CHPA. Lacking metals, CprK is oxygen-sensitive. Oxidation by diamide, which converts thiols to the disulfide, inactivates CprK, and reduction of the oxidized protein by dithiothreitol fully restores DNA binding, indicating that CprK is redox-regulated and is active only when reduced. This is the first reported characterization of a transcriptional regulator of anaerobic dehalorespiration.

Potential for anaerobic conversion of xenobiotics

This review covers the latest research on the anaerobic biodegradation of aromatic xenobiotic compounds, with emphasis on surfactants, polycyclic aromatic hydrocarbons, phthalate esters, polychlorinated biphenyls, halogenated phenols, and pesticides. The versatility of anaerobic reactor systems regarding the treatment of xenobiotics is shown with the focus on the UASB reactor, but the applicability of other reactor designs for treatment of hazardous waste is also included. Bioaugmentation has proved to be a viable technique to enhance a specific activity in anaerobic reactors and recent research on reactor and in situ bioaugmentation is reported.

Identification of a novel PCB source through analysis of 209 PCB congeners by US EPA modified method 1668

PCDD/Fs and PCBs in surface waters and effluent waste streams flowing into New York/New Jersey Harbor were sampled by large volume filtration and solid phase extraction (XAD-2). Passive hexane samplers were employed in sewer trackdown. Extraction media were analyzed for 2,3,7,8 substituted PCDD/Fs and all 209 PCB congeners. The non-Aroclor PCB congener, 3,3'-DiCB, was ubiquitous in the harbor and was found to be associated with pigment manufacture. Knowledge of inadvertent synthesis of non-Aroclor PCBs is not new but its magnitude and the generation of congeners with dioxin-like properties from this process is novel.

Degradation of aroclor 1242 in a single-stage coupled anaerobic/aerobic bioreactor

Degradation of Aroclor 1242 was studied in granular biofilm reactors with limited aeration. An aerobic biphenyl degrader, Rhodococcus sp. M5, was used to supplement a natural bacterial population present in a "bioaugmented" reactor, while the "non-bioaugmented" reactor only contained natural granular sludge. The bioaugmentation, however appeared to have no effect on the reactor performance. Aroclor measurements showed its disappearance in both reactors with only 16-19% of Aroclor recovered from the reactor biomass and effluent. Simultaneously, a chlorine balance indicated that dechlorination occurred at a specific rate of 1.43 mg PCB (g volatile suspended solids)(-1) d(-1), which was comparable to the observed rate of Aroclor disappearance. Intermediates detected in both reactors were biphenyl, benzoic acid, and mono-hydroxybiphenyls. This suggests that a near-complete mineralization of Aroclor can be achieved in a single-stage anaerobic/aerobic system due to a combination of reductive and oxidative degradation mechanisms.

Regiospecific dechlorination of spiked tetra- and trichlorodibenzo-p-dioxins by anaerobic bacteria from PCDD/F-contaminated Spittelwasser sediments

Samples were taken from sediment of the River Spittelwasser (district Bitterfeld, Germany), which is highly polluted with PCDD/Fs and other chloroorganic compounds. The sediment cores were separated into 10-20 cm thick layers, spiked with 50 microM of 1,2,3,4-tetrachlorodibenzo-p-dioxin and incubated for 8 months under anaerobic conditions in the presence of cosubstrates. Reductive dechlorination of the tetrachlorinated congener and formation of tri- and dichlorinated products were observed in all biologically active incubations. Analysis of subcultures spiked with 1,2,3- and 1,2,4-trichlorodibenzo-p-dioxin, respectively, revealed two different dechlorination pathways within the sediment cores. Pathway M was characterized by the simultaneous dechlorination of peri- and lateralchlorine atoms, whereas sequence SP was restricted to the dechlorination at positions flanked by chlorine atoms on both sides.

Microbial growth on dichlorobiphenyls chlorinated on both rings as a sole carbon and energy source

We have isolated bacterial strains capable of aerobic growth on ortho-substituted dichlorobiphenyls as sole carbon and energy sources. During growth on 2,2'-dichlorobiphenyl and 2,4'-dichlorobiphenyl strain SK-4 produced stoichiometric amounts of 2-chlorobenzoate and 4-chlorobenzoate, respectively. Chlorobenzoates were not produced when strain SK-3 was grown on 2,4'-dichlorobiphenyl.

Microbial reductive dehalogenation of polychlorinated biphenyls

Under anaerobic conditions, microbial reductive dechlorination of polychlorinated biphenyls (PCBs) occurs in soils and aquatic sediments. In contrast to dechlorination of supplemented single congeners for which frequently ortho dechlorination has been observed, reductive dechlorination mainly attacks meta and/or para chlorines of PCB mixtures in contaminated sediments, although in a few instances ortho dechlorination of PCBs has been observed. Different microorganisms appear to be responsible for different dechlorination activities and the occurrence of various dehalogenation routes. No axenic cultures of an anaerobic microorganism have been obtained so far. Most probable number determinations indicate that the addition of PCB congeners, as potential electron acceptors, stimulates the growth of PCB-dechlorinating microorganisms. A few PCB-dechlorinating enrichment cultures have been obtained and partially characterized. Temperature, pH, availability of naturally occurring or of supplemented carbon sources, and the presence or absence of H(2) or other electron donors and competing electron acceptors influence the dechlorination rate, extent and route of PCB dechlorination. We conclude from the sum of the experimental data that these factors influence apparently the composition of the active microbial community and thus the routes, the rates and the extent of the dehalogenation. The observed effects are due to the specificity of the dehalogenating bacteria which become active as well as changing interactions between the dehalogenating and non-dehalogenating bacteria. Important interactions include the induced changes in the formation and utilization of H(2) by non-dechlorinating and dechlorinating bacteria, competition for substrates and other electron donors and acceptors, and changes in the formation of acidic fermentation products by heterotrophic and autotrophic acidogenic bacteria leading to changes in the pH of the sediments.

Establishment of a polychlorinated biphenyl-dechlorinating microbial consortium, specific for doubly flanked chlorines, in a defined, sediment-free medium

Estuarine sediment from Charleston Harbor, South Carolina, was used as inoculum for the development of an anaerobic enrichment culture that specifically dechlorinates doubly flanked chlorines (i.e., chlorines bound to carbon that are flanked on both sides by other chlorine-carbon bonds) of polychlorinated biphenyls (PCBs). Dechlorination was restricted to the para chlorine in cultures enriched with 10 mM fumarate, 50 ppm (173 microM) 2,3,4, 5-tetrachlorobiphenyl, and no sediment. Initially the rate of dechlorination decreased upon the removal of sediment from the medium. However, the dechlorinating activity was sustainable, and following sequential transfer in a defined, sediment-free estuarine medium, the activity increased to levels near that observed with sediment. The culture was nonmethanogenic, and molybdate, ampicillin, chloramphenicol, neomycin, and streptomycin inhibited dechlorination activity; bromoethanesulfonate and vancomycin did not. Addition of 17 PCB congeners indicated that the culture specifically removes double flanked chlorines, preferably in the para position, and does not attack ortho chlorines. This is the first microbial consortium shown to para or meta dechlorinate a PCB congener in a defined sediment-free medium. It is the second PCB-dechlorinating enrichment culture to be sustained in the absence of sediment, but its dechlorinating capabilities are entirely different from those of the other sediment-free PCB-dechlorinating culture, an ortho-dechlorinating consortium, and do not match any previously published Aroclor-dechlorinating patterns.

Microbial dechlorination of polychlorinated biphenyls in anaerobic sewage sludge

The potential of a chlorophenol (CP)-adapted consortium to dechlorinate polychlorinated biphenyls (PCBs) in sewage sludge was investigated. Results show that dechlorination rates differed significantly depending on sludge source and PCB congener. Higher total solid concentrations in sewage sludge and higher concentrations of chlorine in PCB resulted in slower dechlorination rates. No significant difference was found for 2,3,4,5-CB dechlorination from pH 6.0 to pH 8.0; however, dechlorination did not occur at pH 9.0 during a 41-day incubation period. Results show that at concentrations of 1 to 10 mg/L, the higher the PCB concentration, the faster the dechlorination rate. In addition, dechlorination rates were in the following order: methanogenic conditions > sulfate-reducing conditions > denitrifying conditions. The addition of acetate, lactate, pyruvate, and ferric chloride decreased lag times and enhanced dechlorination; however, the addition of manganese dioxide had an inhibitory effect. Dechlorination rates were also enhanced by the addition of PCB congeners, including 2,3,4-CB, 2,3,4,5-CB and 2,3,4,5,6-CB in mixture. Overall results show that the CP-adapted consortium has the potential to enhance PCB dechlorination. The optimal dechlorination conditions presented in this paper may be used as a reference for feasibility studies of PCB removal from sludge.

2-Bromoethanesulfonate, sulfate, molybdate, and ethanesulfonate inhibit anaerobic dechlorination of polychlorobiphenyls by pasteurized microorganisms

Dechlorination of Aroclor 1242 by pasteurized microorganisms was inhibited by 2-bromoethanesulfonate (BES), sulfate, molybdate, and ethanesulfonate. Consumption of these anions and production of sulfide from BES were detected. The inhibition could not be relieved by hydrogen. Taken together these results suggest that pattern M dechlorination is mediated by spore-forming sulfidogenic bacteria. These results also suggest that BES may inhibit anaerobic dechlorination by nonmethanogens by more than one mechanism.

Characterization of a defined 2,3,5, 6-tetrachlorobiphenyl-ortho-dechlorinating microbial community by comparative sequence analysis of genes coding for 16S rRNA

Defined microbial communities were developed by combining selective enrichment with molecular monitoring of total community genes coding for 16S rRNAs (16S rDNAs) to identify potential polychlorinated biphenyl (PCB)-dechlorinating anaerobes that ortho dechlorinate 2,3, 5,6-tetrachlorobiphenyl. In enrichment cultures that contained a defined estuarine medium, three fatty acids, and sterile sediment, a Clostridium sp. was predominant in the absence of added PCB, but undescribed species in the delta subgroup of the class Proteobacteria, the low-G+C gram-positive subgroup, the Thermotogales subgroup, and a single species with sequence similarity to the deeply branching species Dehalococcoides ethenogenes were more predominant during active dechlorination of the PCB. Species with high sequence similarities to Methanomicrobiales and Methanosarcinales archaeal subgroups were predominant in both dechlorinating and nondechlorinating enrichment cultures. Deletion of sediment from PCB-dechlorinating enrichment cultures reduced the rate of dechlorination and the diversity of the community. Substitution of sodium acetate for the mixture of three fatty acids increased the rate of dechlorination, further reduced the community diversity, and caused a shift in the predominant species that included restriction fragment length polymorphism patterns not previously detected. Although PCB-dechlorinating cultures were methanogenic, inhibition of methanogenesis and elimination of the archaeal community by addition of bromoethanesulfonic acid only slightly inhibited dechlorination, indicating that the archaea were not required for ortho dechlorination of the congener. Deletion of Clostridium spp. from the community profile by addition of vancomycin only slightly reduced dechlorination. However, addition of sodium molybdate, an inhibitor of sulfate reduction, inhibited dechlorination and deleted selected species from the community profiles of the class Bacteria. With the exception of one 16S rDNA sequence that had the highest sequence similarity to the obligate perchloroethylene-dechlorinating Dehalococcoides, the 16S rDNA sequences associated with PCB ortho dechlorination had high sequence similarities to the delta, low-G+C gram-positive, and Thermotogales subgroups, which all include sulfur-, sulfate-, and/or iron(III)-respiring bacterial species.

Two anaerobic polychlorinated biphenyl-dehalogenating enrichments that exhibit different para-dechlorination specificities

Two anaerobic polychlorinated biphenyl (PCB)-dechlorinating enrichments with distinct substrate specificities were obtained: a 2,3,4,6-tetrachlorobiphenyl (2346-CB) para-dechlorinating enrichment derived from Aroclor 1260-contaminated Woods Pond (Lenox, Mass.) sediment and a 2,4,6-trichlorobiphenyl (246-CB) unflanked para-dechlorinating enrichment derived from PCB-free Sandy Creek Nature Center (Athens, Ga.) sediment. The enrichments have been successfully transferred to autoclaved soil slurries over 20 times by using 300 to 350 microM 2346-CB or 246-CB. Both enrichments required soil for successful transfer of dechlorination activity. The 2346-CB enrichment para dehalogenated, in the absence or presence of 2346-CB, only 4 of 25 tested para halogen-containing congeners: 234-CB, 2345-CB, 2346-CB, and 2,4,6-tribromobiphenyl (246-BrB). In the presence of 246-CB, the 246-CB enrichment para dehalogenated 23 of the 25 tested congeners. However, only three congeners (34-CB, 2346-CB, and 246-BrB) were dehalogenated in the absence of 246-CB, indicating that these specific congeners initiate dehalogenation in this enrichment culture. The addition of the 2346-CB (para)-dechlorinating enrichment did not further stimulate the 2346-CB-primed dechlorination of the Aroclor 1260 residue in Woods Pond sediment samples. Compared to the addition of the primer 246-CB or the 246-CB unflanked para-dechlorinating enrichment alone, the addition of both 246-CB (300 microM) and the 246-CB enrichment stimulated the unflanked para dechlorination of the Aroclor 1260 residue in Woods Pond sediments. These results indicate that the two enrichments contain different PCB-dechlorinating organisms, each with high substrate specificities. Furthermore, bioaugmentation with the enrichment alone did not stimulate the desired dechlorination in PCB-contaminated Woods Pond sediment.

Effect of Incubation Temperature on the Route of Microbial Reductive Dechlorination of 2,3,4,6-Tetrachlorobiphenyl in Polychlorinated Biphenyl (PCB)-Contaminated and PCB-Free Freshwater Sediments

We studied the influence of temperature (4 to 66(deg)C) on the microbial dechlorination of 2,3,4,6-tetrachlorobiphenyl (2,3,4,6-CB) incubated for 1 year in anaerobic sediments from Woods Pond in Lenox, Mass., and Sandy Creek Nature Center Pond (SCNC) in Athens, Ga. Seven discrete dechlorination reactions were observed, four of which occurred in both sediments. These were 2,3,4,6-CB (symbl) 2,4,6-CB, 2,3,4,6-CB (symbl) 2,3,6-CB, 2,4,6-CB (symbl) 2,6-CB, and 2,3,6-CB (symbl) 2,6-CB. Three additional reactions occurred only in Woods Pond sediment. These were 2,4,6-CB (symbl) 2,4-CB, 2,4-CB (symbl) 2-CB, and 2,4-CB (symbl) 4-CB. The dechlorination reactions exhibited at least four different temperature dependencies in SCNC sediment and at least six in Woods Pond sediment. We attribute the discrete dechlorination reactions to different polychlorinated biphenyl (PCB)-dechlorinating microorganisms with distinct specificities. Temperature influenced the timing and the relative predominance of parallel pathways of dechlorination, i.e., meta versus para dechlorination of 2,3,4,6-CB and ortho versus para dechlorination of 2,4,6-CB and 2,4-CB. meta dechlorination of 2,3,4,6-CB to 2,4,6-CB dominated at all tested temperatures except at 18 and 34(deg)C, where para dechlorination to 2,3,6-CB dominated in some replicates. The dechlorination of 2,4,6-CB was restricted to (symbl)15 to 30(deg)C in both sediments. Temperature affected the lag time preceding the dechlorination of 2,4,6-CB in both sediments and affected the preferred route of its dechlorination in Woods Pond sediment. para dechlorination dominated at 20(deg)C, and ortho dechlorination dominated at 15(deg)C, but at 18 and 22 to 30(deg)C the relative dominance of ortho versus para dechlorination of 2,4,6-CB varied. These data indicate that field temperatures play a significant role in controlling the nature and the extent of the PCB dechlorination that occurs at a given site.

Microbial dechlorination of historically present and freshly spiked chlorinated dioxins and diversity of dioxin-dechlorinating populations

The ability of a microbial consortium eluted from dioxin-contaminated Passaic River sediments to dechlorinate polychlorinated dibenzo-p-dioxins (PCDDs) was investigated under methanogenic conditions. Aged 2,3,7,8-tetraCDD, which had partitioned into the microbial consortium from sediments, was stoichiometrically converted to tri- and monoCDD congeners. During dechlorination, dominant microbial activity within the consortium shifted from methanogenic to nonmethanogenic activity. Freshly spiked octaCDD was converted to hepta-, hexa-, penta-, tetra-, tri-, di-, and monochlorinated isomers, but the reaction stoichiometry was not determined. No methanogenic activity was observed, and the maximum yield of protein coincided with the production of less-chlorinated DD congeners. Two distinct pathways of dechlorination were observed: the peri-dechlorination pathway of 2,3,7,8-substituted hepta- to pentaCDDs, resulting in the production of 2,3,7,8-tetraCDD, and the peri-lateral dechlorination pathway of non-2,3,7,8-substituted congeners. Direct evidence of further lateral dechlorination of 2,3,7,8-tetraCDD was obtained from the historically contaminated incubations; no isomer-specific identification of triCDDs in spiked incubations was determined. Pasteurized cells exhibited no peri-dechlorination pathway, and triCDDs were the least-chlorinated congeners produced in these treatments. These results demonstrate that (i) both freshly spiked and aged PCDDs are available to microbial reductive dechlorination, (ii) the peri and triCDD dechlorinations are attributed to activities of nonmethanogenic, non-spore-forming microbial subpopulations, and (iii) the 2,3,7,8-residue patterns in historically contaminated sediments are likely affected by microbial activity.

Effect of oxygen and storage conditions on the metabolic activities of polychlorinated biphenyls dechlorinating microbial granules

The effect of oxygen and storage conditions on the metabolic activities, measured by volatile fatty acid (VFA) degradation and methane production, and by the dechlorinating activity of methanogenic polychlorinated biphenyl (PCB) granules, were studied. Incubation of the granules in air for different periods did not result in significant inhibition in volatile fatty acid degradation and methane production activities. The inhibitory effect of oxygen increased with increased length of exposure. The overall methanogenic activities, however, recovered after a 10-day incubation period in the absence of oxygen. Oxygen exposure did not cause any significant effect on the dechlorinating activity of the granules tested with a PCB mixture, Aroclor 1254. In 6 months, approximately 80% [based on the concentration (microM) of chlorine removed] of the Aroclor 1254 was dechlorinated even by granules exposed to oxygen for 168 h. Granules stored at room temperature (20 degrees C) appeared to be more active compared to the granules stored at 4 degrees C or -20 degrees C. Similarly, granules stored with a nutrient mixture, containing methanol, glucose and yeast extract showed higher metabolic activities. Our results demonstrate that the effect of oxygen exposure was not significant and was reversible. PCB granules could be stored at room temperature with an auxiliary carbon source in the presence of PCB without significant loss of activity. These properties make methanogenic PCB granules suitable candidates for practical use in PCB dechlorination and biodetoxification.

Evidence for para dechlorination of polychlorobiphenyls by methanogenic bacteria

When microorganisms eluted from upper Hudson River sediment were cultured without any substrate except polychlorobiphenyl (PCB)-free Hudson River sediment, methane formation was the terminal step of the anaerobic food chain. In sediments containing Aroclor 1242, addition of eubacterium-inhibiting antibiotics, which should have directly inhibited fermentative bacteria and thereby should have indirectly inhibited methanogens, resulted in no dechlorination activity or methane production. However, when substrates for methanogenic bacteria were provided along with the antibiotics (to free the methanogens from dependence on eubacteria), concomitant methane production and dechlorination of PCBs were observed. The dechlorination of Aroclor 1242 was from the para positions, a pattern distinctly different from, and more limited than, the pattern observed with untreated or pasteurized inocula. Both methane production and dechlorination in cultures amended with antibiotics plus methanogenic substrates were inhibited by 2-bromoethanesulfonic acid. These results suggest that the methanogenic bacteria are among the physiological groups capable of anaerobic dechlorination of PCBs, but that the dechlorination observed with methanogenic bacteria is less extensive than the dechlorination observed with more complex anaerobic consortia.

Biotransformations of Aroclor 1242 in Hudson River test tube microcosms

A microcosm system to physically model the fate of Aroclor 1242 in Hudson River sediment was developed. In the dark at 22 to 25 degrees C with no amendments (nutrients, organisms, or mixing) and with overlying water being the only source of oxygen, the microcosms developed visibly distinct aerobic and anaerobic compartments in 2 to 4 weeks. Extensive polychlorinated biphenyl (PCB) biodegradation was observed in 140 days. Autoclaved controls were unchanged throughout the experiments. In the surface sediments of these microcosms, the PCBs were biologically altered by both aerobic biodegrading and reductive dechlorinating microorganisms, decreasing the total concentration from 64.8 to 18.0 micromol/kg of sediment in 1140 days. This is the first laboratory demonstration of meta dechlorination plus aerobic biodegradation in stationary sediments. In contrast, the primary mechanism of microbiological attack on PCBs in aerobic subsurface sediments was reductive dechlorination. The concentration of PCBs remained constant at 64.8 micromol/kg of sediment, but the average number of chlorines per biphenyl decreased from 3.11 to 1.84 in 140 days. The selectivities of microorganisms in these sediments were characterized by meta and para dechlorination. Our results provide persuasive evidence that naturally occurring microorganisms in the Hudson River have the potential to attack the PCBs from Aroclor 1242 releases both aerobically and anaerobically at rapid rates. These unamended microcosms represent a unique method for determining the fate of released PCBs in river sediments.

Screening and Separation of Microorganisms Degrading PCBs

We performed an assay to assess the polychlorinated biphenyl (PCB) degradative capability and congener specificity of aerobic microorganisms. Microbial strains were isolated and separated from different types of soils in the Czech Republic, and their PCB-degrading abilities were compared. An industrial mixture of PCB congeners ranging from dichloro- to hexachlorobiphenyl and representing various chlorination patterns was used throughout. The PCB degradative ability of microorganisms was determined by gas chromatography after 7 days of incubation. The degree of degradation was found to depend on the number of chlorine substituents.

Effects of Polychlorinated Biphenyl Congener Concentration and Sediment Supplementation on Rates of Methanogenesis and 2,3,6-Trichlorobiphenyl Dechlorination in an Anaerobic Enrichment

We have employed a method of enrichment that allows us to significantly increase the rate of reductive polychlorinated biphenyl (PCB) dechlorination. This method shortens the time required to investigate the effects that culture conditions have on dechlorination and provides an estimate of the potential activity of the PCB-dechlorinating anaerobes. The periodic supplementation of sterile sediment and PCB produced an enhanced, measurable, and sustained rate of dechlorination. We observed volumetric rates of the dechlorination of 2,3,6-trichlorobiphenyl (2,3,6-CB) to 2,6-dichlorobiphenyl (2,6-CB) of more than 300 μmol liter -1 day -1 when the cultures were supplemented daily. A calculation of this activity that is based on an estimate of the number of dechlorinating anaerobes present indicates that 1.13 pmol of 2,3,6-CB was dechlorinated to 2,6-CB day -1 bacterial cell -1 . This rate is similar to that of the reductive dechlorination of 3-chlorobenzoate by Desulfomonile tiedjei. Methanogenesis declined from 585.3 to 125.9 μmol of CH 4 liter -1 day -1 , while dechlorination increased from 8.2 to 346.0 μmol of 2,3,6-CB dechlorinated to 2,6-CB liter -1 day -1 .

Degradation of Aroclor 1221 in soil by a hybrid pseudomonad

The hybrid Pseudomonas cepacia strain JHR22 was tested for its ability to degrade Aroclor 1221 in soil. The influence of supplements--mineral salts and trace elements--on the degradation was investigated. Disappearance of Aroclor 1221 congeners, occurrence of metabolites, and release of chloride were measured under different conditions. After 45 days the hybrid organism, strain JHR22, was still present at high numbers in soil, independently of whether the soil had been sterilized prior to inoculation or not. There was only a minor difference in degradation efficiency between sterilized and untreated soil with about 70% release of chloride when 10(7) cells/g soil were inoculated. The whole hybrid pathway, originating from three different strains, was found to be stable under the conditions tested. Mineral salts did not significantly affect the degradation rate or survival of the hybrid strain.

Subculturing of a polychlorinated biphenyl-dechlorinating anaerobic enrichment on solid media

An anaerobic culture capable of dechlorinating polychlorinated biphenyls was subcultured under strict anaerobic conditions on solid media containing sterilized river sediment. The dechlorination activity was transferred as a bacterial colony on a solid medium three times. After two transfers on solid medium, the culture was no longer methanogenic but still dechlorinated a mixture of tri- and tetrachlorobiphenyls. This demonstrates that anaerobic bacteria are responsible for the polychlorinated biphenyl dechlorination and can be grown without polychlorinated biphenyl on solid media.

Isolation and characterization of an anaerobic chlorophenol-transforming bacterium

An obligately anaerobic bacterium which transforms several chlorinated phenols was isolated. Dechlorination of the substituents ortho to the phenolic OH group was preferred, while removal of a meta-substituted chlorine was observed only with 3,5-dichlorophenol. The bacterium was a gram-positive, endospore-forming, motile, slightly curved rod. Sulfate was not reduced. Nitrate was reduced via nitrite to ammonium. The bacterium is related to the genus Clostridium. The highest growth rate was obtained in a medium containing pyruvate and yeast extract. Pyruvate supported growth as the sole source of carbon, and the fermentation of pyruvate produced almost equimolar amounts of acetate.

Establishment of polychlorinated biphenyl-degrading enrichment culture with predominantly meta dechlorination

Enrichment of polychlorinated biphenyl (PCB)-dechlorinating microorganisms from PCB-contaminated sediments from the Upper Hudson River, N.Y., was attempted. The enrichment strategy was to use pyruvate as the electron donor and dechlorination of Aroclor 1242 as the electron acceptor. The enrichment medium also contained non-PCB-contaminated Hudson River sediments, which were required for the PCB-dechlorinating activity. An enrichment culture (that had stable PCBT-dechlorinating activity over nine serial transfers during 1 year) was established under these conditions; however, the rate of dechlorination did not increase after the second serial transfer. Dechlorination occurred primarily from the meta positions of the biphenyl molecule. Hydrogen could be substituted for pyruvate as the electron donor with equal activity, but when acetate was used as the electron donor a delay in dechlorination was observed. Sulfate and bromethane sulfonate inhibited dechlorination activity. The pyruvate-Aroclor 1242 enrichment also dechlorinated Aroclors 1248, 1254, and 1260; the extent of chlorine removed was the greatest for Aroclor 1254. For comparison, nonautoclaved non-PCB-contaminated Hudson River sediments used in the assay also dechlorinated Aroclors, but only after 12 to 16 weeks of incubation. This suggests that PCB-dechlorinating organisms were also present in these sediments but in numbers lower than those in the enrichment culture.