Degradation of polychlorinated biphenyl (PCB) by a consortium obtained from a contaminated soil composed of Brevibacterium,Pandoraea and Ochrobactrum

An indigenous polychlorinated biphenyl (PCB)-degrading bacterial consortium was obtained from soils contaminated by transformer oil with a high content of PCBs. The PCB degrader strains were isolated and identified as Brevibacterium antarcticum, Pandoraea pnomenusa, and Ochrobactrum intermedium by 16S rRNA gene sequence phylogenetic analysis. The PCB-degrading ability of the consortium and of individual strains was determined by using GC/MS. The PCB-degrading capacities of the consortium were evaluated for three concentrations of transfomer oil ranging from 55 to 152 μM supplemented with 0.001% biphenyl and 0.1% of Tween 80 surfactant. PCB biodegradation by the consortium was favored in the presence of both additives and the greatest extent of biodegradation (67.5%) was obtained at a PCB concentration of 55 μM. Each bacterial species exhibited a particular pattern of degradation relating to specific PCB congeners. Isolated strains showed a moderate degradation capability towards tetra-, hepta-, and octa-chlorobiphenyls; although no effect on penta-, hexa-, and nona-chlorobiphenyls was observed. Recently, PCB degradation capacity was recognized in a Pandorea member; however, this is the first study that describes the ability of Brevibacterium and Ochrobactrum species to degrade PCBs.     

Degradation and dechlorination of low-chlorinated biphenyls by a three-membered bacterial co-culture

A Pseudomonas sp. strain, designated CPE1, was found to be capable of completely mineralizing 4-chlorobiphenyl via 4-chlorobenzoate and of partially dechlorinating 3,4-dichlorobiphenyl in the presence of biphenyl. A three-membered bacterial consortium, designated ECO3, prepared by combining CPE1 with two chlorobenzoate (CBA)-degrading strains, was capable of extensively degrading and dechlorinating all the monochlorinated biphenyls and several dichlorinated biphenyls in the presence of bipheny. Both CPE1 and ECO3 were capable of co-metabolizing several low-chlorinated biphenyl congeners of Fenclor 42 in the presence of biphenyl; however, only in ECO3 cultures were high degradation rates and chloride release observed. The higher rate of degradation and mineralization of some polychlorinated biphenyls (PCBs) of Fenclor 42 due to the concerted action of ECO3 members both on PCBs and CBAs suggested that the removal of CBAs from the culture medium may favour PCB degradation, and, therefore, that CBAs may be ivollved in the regulation of the degradation process of several chlorinated biphenyl congeners.Correspoeence to: F. Fava     

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.     

Aerobic degradation of highly chlorinated polychlorobiphenyls by a marine bacterium, Pseudomonas CH07

Hitherto, aerobic degradation of polychlorinated biphenyls (PCBs) has been reported to be limited to the less chlorinated biphenyls. We report here a marine mercury-resistant bacterium, Pseudomonas CH07 (NRRL B-30604) which was capable of degrading a variety of highly chlorinated congeners of PCBs from the technical mixture Clophen A-50. Of the two most toxic coplanar PCBs present in Clophen A-50, one coplanar pentachloro congener CB-126 and one toxic sterically hindered heptachloro congener CB-181 were found to be degraded completely and the other coplanar tetrachloro congener CB-77 was degraded by more than 40% within 40 h by this microorganism. The apparent absence of bphC in this bacterium leads to the proposal of a different mechanism for degradation of PCBs.     

Bacterial metabolism of polychlorinated biphenyls

Microbial metabolism is responsible for the removal of persistent organic pollutants including PCBs from the environment. Anaerobic dehalogenation of highly chlorinated congeners in aquatic sediments is an important process, and recent evidence has indicated that Dehalococcoides and related organisms are predominantly responsible for this process. Such anaerobic dehalogenation generates lower chlorinated congeners which are easily degraded aerobically by enzymes of the biphenyl upper pathway (bph). Initial biphenyl 2,3-dioxygenases are generally considered the key enzymes of this pathway which determine substrate range and extent of PCB degradation. These enzymes have been subject to different protein evolution strategies, and subsequent enzymes have been considered as crucial for metabolism. Significant advances have been made regarding the mechanistic understanding of these enzymes, which has also included elucidation of the function of BphK glutathione transferase. So far, the genomes of two important PCB-metabolizing organisms, namely Burkholderia xenovorans strain LB400 and Rhodococcus sp. strain RHA1, have been sequenced, with the rational to better understand their overall physiology and evolution. Genomic and proteomic analysis also allowed a better evaluation of PCB toxicity. Like all bph gene clusters which have been characterized in detail, particularly in strains LB400 and RHA1, these genes were localized on mobile genetic elements endowing single strains and microbial communities with a high flexibility and adaptability. However, studies show that our knowledge on enzymes and genes involved in PCB metabolism is still rather fragmentary and that the diversity of bacterial strategies is highly underestimated. Overall, metabolism of biphenyl and PCBs should not be regarded as a simple linear pathway, but as a complex interplay between different catabolic gene modules.     

多氯联苯降解菌Burkholderia xenovorans LB400研究进展

Burkholderia xenovorans LB400是一株多氯联苯(polychlorinated biphenyls,PCBs)降解菌,可以氧化含有1?6个氯取代基的多氯联苯。近年来,由于其广泛的底物谱和优异的降解性能,菌株LB400已成为研究原核生物降解多氯联苯的生物化学和分子生物学方面的模式生物。目前关于PCBs的微生物降解研究已不再局限于对微生物资源的挖掘,而是更多地聚焦在LB400等降解菌的PCBs降解基因、降解酶的酶学特性以及酶的人工分子进化等方面。同时,LB400作为早期发现的降解菌,其对多氯联苯的降解途径、底物范围及相关机制也被广泛探讨;但是对于PCBs降解相关基因的调控研究较少。因此,本文以Burkholderia xenovorans LB400对多氯联苯降解为核心,通过综述其代谢途径、代谢相关基因和酶系以及降解应用等方面的研究进展,以期为深入探讨Burkholderia xenovorans LB400的应用以及进一步在遗传、分子和生化水平研究其他多氯联苯降解菌株提供借鉴。     

Chlorinated biphenyl mineralization by individual populations and consortia of freshwater bacteria.

Comparative studies were performed to investigate the contribution of microbial consortia, individual microbial populations, and specific plasmids to chlorinated biphenyl biodegradation among microbial communities from a polychlorinated biphenyl-contaminated freshwater environment. A bacterial consortium, designated LPS10, was shown to mineralize 4-chlorobiphenyl (4CB) and dehalogenate 4,4'-dichlorobiphenyl. The LPS10 consortium involved three isolates: Pseudomonas testosteroni (LPS10A), which mediated the breakdown of 4CB and 4,4'-dichlorobiphenyl to 4-chlorobenzoic acid; an isolate tentatively identified as an Arthrobacter sp. (LPS10B), which mediated 4-chlorobenzoic acid degradation; and Pseudomonas putida bv. A (LPS10C), whose role in the consortium has not been determined. None of these isolates contained detectable plasmids or sequences homologous to the 4CB-degradative plasmid pSS50. A freshwater isolate, designated LBS1C1, was found to harbor a 41-megadalton plasmid that was related to the 35-megadalton plasmid pSS50, and this isolate was shown to mineralize 4CB. In chemostat enrichments with biphenyl and 4CB as primary carbon sources, the LPS10 consortium was found to outcomplete bacterial populations harboring plasmids homologous to pSS50. These results demonstrate that an understanding of the biodegradative capacity of individual bacterial populations as well as interacting populations of bacteria must be considered in order to gain a better understanding of polychlorinated biphenyl biodegradation in the environment.     

Chlorinated biphenyl mineralization by individual populations and consortia of freshwater bacteria

Comparative studies were performed to investigate the contribution of microbial consortia, individual microbial populations, and specific plasmids to chlorinated biphenyl biodegradation among microbial communities from a polychlorinated biphenyl-contaminated freshwater environment. A bacterial consortium, designated LPS10, was shown to mineralize 4-chlorobiphenyl (4CB) and dehalogenate 4,4'-dichlorobiphenyl. The LPS10 consortium involved three isolates: Pseudomonas testosteroni (LPS10A), which mediated the breakdown of 4CB and 4,4'-dichlorobiphenyl to 4-chlorobenzoic acid; an isolate tentatively identified as an Arthrobacter sp. (LPS10B), which mediated 4-chlorobenzoic acid degradation; and Pseudomonas putida bv. A (LPS10C), whose role in the consortium has not been determined. None of these isolates contained detectable plasmids or sequences homologous to the 4CB-degradative plasmid pSS50. A freshwater isolate, designated LBS1C1, was found to harbor a 41-megadalton plasmid that was related to the 35-megadalton plasmid pSS50, and this isolate was shown to mineralize 4CB. In chemostat enrichments with biphenyl and 4CB as primary carbon sources, the LPS10 consortium was found to outcomplete bacterial populations harboring plasmids homologous to pSS50. These results demonstrate that an understanding of the biodegradative capacity of individual bacterial populations as well as interacting populations of bacteria must be considered in order to gain a better understanding of polychlorinated biphenyl biodegradation in the environment.     

Isolation and Characterization of a Mixed Culture That Degrades Polychlorinated Biphenyls

A mixed culture composed of two Pseudomonas strains, designated as KKL101 and KKS102, was isolated from soil. This mixed culture had an enhanced ability to degrade various polychlorinated biphenyls (PCBs) which include highly chlorinated components. They did not grow individually on the mineral salts medium supplemented with a highly chlorinated PCB (PCB48, a mixture of mainly tetrachlorobiphenyl) and biphenyl. When the spent medium of KKL101 was added to the washed cell preparation of KKS102, however, the latter grew on these carbon sources, producing yellow compounds which were identified as metabolic intermediates of the carbon sources, biphenyl and PCBs. These results suggest that KKL101 produces a growth factor(s) essential for KKS102 to grow on PCBs and that the growth of KKL101 is supported by the metabolic intermediates produced by KKS102. It appears that these two bacterial strains have a symbiotic relationship. From the analysis of the degradation products of various PCB congeners, it was found that strain KKS102 degrades a wide range of PCBs which have been considered to be refractory to biological degradation.     

Geographic variation of PCB congeners in polar bears (Ursus maritimus) from Svalbard east to the Chukchi Sea

We present data on geographic variation in polychlorinated biphenyl (PCB) congeners in adult female polar bears (Ursus maritimus) from Svalbard eastward to the Chukchi Sea. Blood samples from 90 free-living polar bears were collected in 1987-1995. Six PCB congeners, penta to octa chlorinated (PCB-99, -118, -153, -156, -180, -194), were selected for this study. Differences between areas were found in PCB levels and congener patterns. Bears from Franz Josef Land (11,194 ng/g lipid weight) and the Kara Sea (9,412 ng/g lw) had similar DPCB levels and were higher than all other populations (Svalbard 5,043 ng/g lw, East Siberian Sea 3,564 ng/g lw, Chukchi Sea 2,465 ng/g lw). Svalbard PCB levels were higher than those from the Chukchi Sea. Our results, combined with earlier findings, indicate that polar bears from Franz Josef Land and the Kara Sea have the highest PCB levels in the Arctic. Decreasing trends were seen eastwards and westwards from this region. Of the congeners investigated in the present study, the lower chlorinated PCBs are increasing and the high chlorinated PCBs are decreasing from Svalbard eastward to the Chukchi Sea. Different pollution sources, compound transport patterns and regional prey differences could explain the variation in PCB congener levels and patterns between regions.     

Transformation of polychlorinated biphenyls by a novel BphA variant through the meta-cleavage pathway

The transformation of 20 polychlorinated biphenyls (PCBs) through the meta-cleavage pathway by recombinant Escherichia coli cells expressing the bphEFGBC locus from Burkholderia cepacia LB400 and the bphA genes from different sources was compared. The analysis of PCB congeners for which hydroxylation was observed but no formation of the corresponding yellow meta-cleavage product demonstrated that only lightly chlorinated congeners including one tetrachlorobiphenyl (2,2',4,4'-CB) were transformed into their corresponding yellow meta-cleavage products. Although many other tetrachlorobiphenyls (2, 2',5,5'-CB, 2,2',3,5'-CB, 2,4,4',5-CB, 2,3',4',5-CB, 2,3',4,4'-CB) and one pentachlorobiphenyl (2,2',4,5,5'-CB) tested were depleted from resting cell suspensions, no yellow meta-cleavage products were observed. For most of these congeners, dihydrodiol compounds accumulated as the endproducts, indicating that the bphB-encoded biphenyl-2,3-dihydrodiol-2,3-dehydrogenase is a key limiting step for further degradation of highly chlorinated congeners. These results suggest that engineering the biphenyl dioxygenase alone is insufficient for an improved removal of PCB. Rather, improved degradation of PCBs is more likely to be achieved with recombinant strains containing metabolic pathways not only specifically engineered for expanding the initial dioxygenation but also for the mineralization of PCBs.     

Dechlorination of polychlorinated biphenyl congeners by an anaerobic microbial consortium

  An anaerobic methanogenic microbial consortium, developed in a granular form, exhibited extensive dechlorination of defined polychlorinated biphenyl (PCB) congeners. A 2,3,4,5,6-pentachlorobiphenyl was dechlorinated to biphenyl via 2,3,4,6-tetrachlorobiphenyl, 2,4,6-trichlorobiphenyl, 2,4-dichlorobi-phenyl and 2-chlorobiphenyl (CB). Removal of chlorine atoms from all three positions of the biphenyl ring, i.e., ortho, meta and para, was observed during this reductive dechlorination process. Biphenyl was identified as one of the end-products of the reductive dechlorination by GC-MS. After 20 weeks, the concentrations of the dechlorination products 2,4,6-CB, 2,4-CB, 2-CB and biphenyl were 8.1, 41.2, 3.0 and 47.8 μM respectively, from an initial 105 μM 2,3,4,5,6-CB. The extent and pattern of the dechlorination were further confirmed by the dechlorination of lightly chlorinated congeners including 2-CB, 3-CB, 4-CB, 2,4-CB and 2,6-CB individually. This study indicates that the dechlorination of 2,3,4,5,6-CB to biphenyl is due to ortho, meta and para dechlorination by this anaerobic microbial consortium. Received: 30 April 1996 / Received revision: 26 July 1996 / Accepted: 5 August 1996     

Root exudates and plant secondary metabolites of different plants enhance polychlorinated biphenyl degradation by rhizobacteria

Polychlorinated biphenyls (PCBs) are toxic and persistent compounds that are difficult to break down and biodegrade. Plant secondary metabolites (PSMs) on root exudates can act as inducers of the biphenyl catabolic pathway, enhancing PCB biodegradation. In this study, the authors evaluated the effect of root exudates and PSMs obtained from Avena sativa, Brachiaria decumbens, Medicago sativa, and Brassica juncea on the biodegradation of PCB 44, PCB 66, PCB 118, PCB 138, PCB 153, PCB 170, and PCB 180 by a microbial consortium isolated from the rhizosphere of plants grown on soil contaminated with Aroclor 1260. Microorganisms were identified as Pseudomonas sp. and Stenotrophomonas sp. based on their 16S rRNA sequence. The plant root exudates increased the degradation percentage of PCB 44, PCB 66, and PCB 118, which were used as carbon source by the microorganisms. Flavanone, flavone, isoflavone, 7-hydroxyflavanone, 7-hydroxyflavone, and 6-hydroxyflavone were the PSMs identified in the root exudates, which increased the degradation percentage of all seven PCB congeners; they were also used as growth substrates by microbial consortium. These results showed the importance of the interaction between plants and microorganisms for achieving the removal of persistent pollutants such as PCBs from soil.     

Mineralization of biphenyl and PCBs by the white rot fungus Phanerochaete chrysosporium

The white rot fungus Phanerochaete chrysosporium is unique in its ability to totally degrade a wide variety of recalcitrant pollutants. We have investigated the degradation of biphenyl and two model chlorinated biphenyls, 2,2',4,4'-tetrachlorobiphenyl and 2-chlorobiphenyl by suspended cultures of P. chrysosporium grown under conditions that maximize the synthesis of lignin-oxidizing enzymes. Radiolabeled biphenyl and 2'-chlorobiphenyl added to cultures at concentrations in the range 260 nM to 8.8 muM were degraded extensively to CO(2) within 30 days. In addition, from 40% to 60% of the recovered radioactivity was found in water-soluble compounds. A correlation between the rate of degradation and the synthesis of ligninases or Mn-dependent peroxidases could not be observed, indicating that yet unknown enzymatic system may be resonsible for the initial oxidation of PCBs. The more heavily chlorinated PCB congener, 2,2',4,4'-tetrachlorobiphenyl was converted to CO(2) less readily; approximately 9% and 0.9% mineralization was observed in cultures incubated with 40 nM and 5.3 muM, respectively. Overall, our results indicate that P. chrysosporium is a promising organism for the treatment of wastes contaminatd with lightly and moderately chlorinated PCBs. (c) 1992 John Wiley & Sons, Inc.     

Involvement of mixed function oxidase systems in polychlorinated biphenyl metabolism by plant cells

Summary Nineteen different polychlorinated biphenyl (PCB) congeners ranging in chlorine content from 2 to 6 chlorine atoms were provided to nonphotosynthetic suspension cultures of rose (Rosa sp. cv. Paul's Scarlet). After a 96 h incubation period, 11 individual congeners had been metabolized by > 10%. Provision of mixed function oxidase inhibitors (10 mM metyrapone or 0.5 mM 7,8-benzoflavone) either stopped or severely reduced the metabolism of individual congeners; whereas (inhibitors of peroxidase) (1 mM benzoate or 1 mM n-propylgallate) had minimal influence on PCB metabolism. The metabolism of PCBs by rose cultures appears to be catalyzed by a cytochrome P-450-and/or P-448-dependent enzyme system.     

Accumulation of polychlorinated biphenyls in adipocytes: selective targeting to lipid droplets and role of caveolin-1

Background

Polychlorinated biphenyls (PCBs) are persistent environmental pollutants that preferentially accumulate in lipid-rich tissues of contaminated organisms. Although the adipose tissue constitutes a major intern reservoir of PCBs and recent epidemiological studies associate PCBs to the development of obesity and its related disorders, little is known about the mechanisms involved in their uptake by the adipose tissue and their intracellular localization in fat cells.

Methodology/Principal Findings

We have examined the intracellular distribution of PCBs in mouse cultured adipocytes and tested the potential involvement of caveolin-1, an abundant adipocyte membrane protein, in the uptake of these compounds by fat cells. We show that 2,4,4′-trichlorobiphenyl (PCB-28), 2,3′,4,4′,5-pentachlorobiphenyl (PCB-118) and 2,2′,4,4′,5,5′-hexachlorobiphenyl (PCB-153) congeners rapidly and extensively accumulate in 3T3-L1 or mouse embryonic fibroblast (MEF) derived cultured adipocytes. The dynamics of accumulation differed between the 3 congeners tested. By subcellular fractionation of primary adipocytes, we demonstrate that these pollutants were almost exclusively recovered within the lipid droplet fraction and practically not associated to cell membranes. The absence of caveolin-1 expression in primary adipocytes from cav-1 deficient mice did not modify lipid droplet selective targeting of PCBs. In cav-1 KO MEF differentiated adipocytes, PCB accumulation was decreased, which correlated with reduced cell triglyceride content. Conversely, adenoviral mediated cav-1 overexpressing in 3T3-L1 cells, which had no impact on total cell lipid content, did not change PCB accumulation.

Conclusion/Significance

Our data indicate that caveolin-1 per se is not required for selective PCB accumulation, but rather point out a primary dependence on adipocyte triglyceride content. If the crucial role of lipid droplets in energy homeostasis is considered, the almost exclusive accumulation of PCBs in these organelles warrants future attention as the impairment of their function could be linked to the worldwide obesity epidemic.     

Psychrotolerant Bacteria Isolated from Arctic Soil That Degrade Polychlorinated Biphenyls at Low Temperatures

Psychrotolerant polychlorinated biphenyl (PCB)-degrading bacteria were isolated at 7°C from PCB-contaminated Arctic soil by using biphenyl as the sole organic carbon source. These isolates were distinguished from each other by differences in substrates that supported growth and substrates that were oxidized. 16S ribosomal DNA sequences suggest that these isolates are most closely related to the genus Pseudomonas. Total removal of Aroclor 1242, and rates of removal of selected PCB congeners, by cell suspensions of Arctic soil isolates and the mesophile Burkholderia cepacia LB400 were determined at 7, 37, and 50°C. Total removal values of Aroclor 1242 at 7°C by LB400 and most Arctic soil isolates were similar (between 2 and 3.5 μg of PCBs per mg of cell protein). However the rates of removal of some individual PCB congeners by Arctic isolates were up to 10 times higher than corresponding rates of removal by LB400. Total removal of Aroclor 1242 and the rates of removal of individual congeners by the Arctic soil bacteria were higher at 37°C than at 7°C but as much as 90% lower at 50°C than at 37°C. In contrast, rates of PCB removal by LB400 were higher at 50°C than at 37°C. In all cases, temperature did not affect the congener specificity of the bacteria. These observations suggest that the PCB-degrading enzyme systems of the bacteria isolated from Arctic soil are cold adapted.     

Congener Selectivity During Polychlorinated Biphenyls Degradation by Enterobacter sp. LY402

The relationship between the selectivity of a particular polychlorinated biphenyls (PCBs) congener and its biodegradability under the same concentration, especially by Enterobacter sp. LY402, is less well studied. To measure congener selectivity of Enterobacter sp. LY402, several influencing factors were studied. The results showed LY402 effectively degraded coplanar 3,4,3',4'-chlorobiphenyl (CB) at a concentration of 0.05 μM, but not 0.5 μM. The degradation rates of 2,4,5,2',3'-CB and 2,4,5,2',4',5'-CB were increased significantly when the sample constituents were changed from 12 to 5 congeners or to one congener. This indicated that bioremediation of individual congener was affected by other congeners present in the mixture. Moreover, for PCBs containing one chlorine on each phenyl ring, the reactivity preference of LY402 was 2,2'-CB ≥ 3,3'-CB ? 4,4'-CB. For two ortho chlorines congeners of PCBs, 2,2'-CB was degraded faster than 2,6-CB. Although 2,6-CB and 4,4'-CB were poorly degraded, the addition of one (i.e., 2,4,4'-CB and 2,6,3'-CB) or two more chlorines (i.e., 2,4,2',4'-CB) on the phenyl ring significantly increased their biodegradability. In addition, comparing the two congeners of ortho-meta-chlorinated biphenyl, 2,3,2',3'-CB with neighbor meta chlorines was degraded slower than 2,5,2',5'-CB with interval meta chlorines. All these indicated that the transformation rates of PCBs were not consistent with the number of chlorines, and PCBs containing the same numbers of chlorines but at different positions also resulted in different conversions. In principle, the extents of effect caused by the position of chlorine substituents on the degradation of PCBs by LY402 were ortho- > meta- > para-CB. In conclusion, the congener selectivity of LY402 was determined by many factors, including the composition of the congeners, their concentrations in the mixture and location and number of chlorine substituents on the phenyl rings.     

Bioaugmentation with Immobilized Microorganisms to Enhance Phytoremediation of PCB-Contaminated Soil

The aim of this study was evaluate the effect of bioaugmentation by free and immobilized strains of microbial consortium on the phytoremediation of polychlorinated biphenyl (PCB)-contaminated soil using the Avena sativa, Brachiaria decumbens, Brassica juncea, and Medicago sativa plants. Alginate and biochar were used as carrier materials and free cells were used as the control. PCBs 44, 66, 118, 138, 153, 170, and 180 were chosen as indicator PCB congeners. After 60 days of plant growth, the concentration of each congener and the survival of the microbial inoculum were evaluated. The removal of the PCB congener was greater in B. juncea planted treatments and using biochar as a carrier material. PCB 66 was the congener with the highest removal percentage in all using biochar and alginate-immobilized microorganisms and free microorganisms, while PCB 170 had the lowest removal percentage in all treatments. The largest removal percentage for all congeners was obtained using biochar as a carrier material (7.2–30.3%) and the lowest with planted treatments using free microorganisms (2.3–6.8%). Real-time polymerase chain reaction (PCR) showed that the microbial inoculum survived when it was immobilized using both alginate and biochar without any significant differences between treatments; however, PCB removal percentages were obtained with biochar, which demonstrated that this carrier material has a positive effect on microbial activity.     

Rapid assay for screening and characterizing microorganisms for the ability to degrade polychlorinated biphenyls

We designed a rapid assay that assesses the polychlorinated biphenyl (PCB)-degradative competence and congener specificity of aerobic microorganisms, identifies strains capable of degrading highly chlorinated biphenyls, and distinguishes among those that degrade PCBs by alternative pathways. Prior attempts to assay PCB-degradative competence by measuring disappearance of Aroclors (commercial PCB mixtures) have frequently produced false-positive findings because of volatilization, adsorption, or absorption losses. Furthermore, these assays have generally left the chemical nature of the competence obscure because of incomplete gas chromatographic resolution and uncertain identification of Aroclor peaks. We avoided these problems by using defined mixtures of PCB congeners and by adopting incubation and extraction methods that prevent physical loss of PCBs. Our assay mixtures include PCB congeners ranging from dichloro- to hexachlorobiphenyls and representing various structural classes, e.g., congeners chlorinated on a single ring (2,3-dichlorobiphenyl), blocked at 2,3 sites (2,5,2'5'-tetrachlorobiphenyl), blocked at 3,4 sites (4,4'-dichlorobiphenyl), and lacking adjacent unchlorinated sites (2,4,5,2',4',5'-hexachlorobiphenyl). The PCB-degrative ability of microorganisms is assessed by packed-column gas chromatographic analysis of these defined congener mixtures following 24-h incubation with resting cells. When tested with 25 environmental isolates, this assay revealed a broad range of PCB-degradative competence, highlighted differences in congener specificity and in the extent of degradation of individual congeners, predicted degradative competence on commercial PCBs, and (iv) identified strains with superior PCB-degradative ability.