Compound degraded:Polychlorinated biphenyls (PCB)

General Description (About POP compound)

Polychlorinated biphenyls (PCBs) are organic chemicals with characteristics similar to that of DDT. They were produced commercially by catalytic chlorination of biphenyls producing a complex mixture of multiple isomers with different degrees of chlorination yielding up to 209 products called congeners. PCB congeners with the same number of chlorine atoms are known as homologs, and the homologs with different chlorine positions are called isomers. PCB mixtures had been widely used in various industrial applications for many years due to their desirable physical and chemical properties. Now they are known to be ubiquitous and persistent contaminants of the environment.

Biodegradation pathway

Publications

Abstract Title Authors Article Link
Polychlorinated biphenyls (PCBs) are one of the persistent organic pollutants (POPs) used worldwide between the 1930 and 1980s. Many PCBs can still be found in the environment such as in soils and sediments, even though their use has been heavily restricted. This review summarizes the most frequent remediation solutions including, phytoremediation, microbial degradation, dehalogenation by chemical reagent, and PCBs removal by activated carbon. New insights that emerged from recent studies of PCBs remediation including supercritical water oxidation, ultrasonic radiation, bimetallic systems, nanoscale zero-valent iron based reductive dehalogenation and biofilm covered activated carbon, electrokinetic remediation, and nZVI particles in combination with a second metal are overviewed. Some of these methods are still in the initial development stage thereby requiring further research attention. In addition, the advantages and disadvantages of each general treatment strategy and promising technology for PCBs remediation are discussed and compared. There is no well-developed single technology, although various possible technologies have been suggested. Therefore, the possibility of using combined technologies for PCB remediation is also here investigated. It is hoped that this present paper can provide a basic framework and a more profound prospect to select successful PCB remediation strategies or combined technologies. Remediation of Polychlorinated Biphenyls (PCBs) in Contaminated Soils and Sediment: State of Knowledge and Perspectives Jing et al., 2018 Link
We investigated the PCB-degrading abilities of four bacterial strains isolated from long-term PCB-contaminated soil (Alcaligenes xylosoxidans and Pseudomonas stutzeri) and sediments (Ochrobactrum anthropi and Pseudomonas veronii) that were co-metabolically grown on glucose plus biphenyl which is an inducer of the PCB catabolic pathway. The aim of study was to determine the respective contribution of biomass increase and expression of degrading enzymes on the PCB degrading abilities of each isolate. Growth on 5 g l?1 glucose alone resulted in the highest stimulation of the growth of bacterial strains, whereas grown on 10 mg l?1, 100 mg l?1, 1 g l?1, or 5 g l?1 biphenyl did not effected the bacterial growth. None of the strains used in this study was able to grow on PCBs as the sole carbon source. Cells grown on glucose exhibited enhanced degradation ability due to an increased biomass. Addition of biphenyl at concentrations of 1 or 5 g l?1 did not increase total PCB degradation, but stimulated the degradation of highly chlorinated congeners for some of the strains. The degradation of di- and tri-chlorobiphenyls was significantly lower for cells grown on 5 g l?1 biphenyl independently on glucose addition. The highest degradation of the PCBs was obtained for A. xylosoxidans grown in the presence of glucose. Thus A. xylosoxidans appears to be the most promising among the four bacterial isolates for the purpose of bioremediation. Degradation of polychlorinated biphenyls (PCBs) by four bacterial isolates obtained from the PCB-contaminated soil and PCB-contaminated sediment Murínová et al., 2014 Link
Polychlorinated biphenyls (PCBs) included with the commercial mixture Delor 103 were degraded by immobilized cells of aerobic bacterial strain Pseudomonas sp. 2. The ability of the strain to metabolise selected tri- and tetrachlorobiphenyls, and the site of primary attack of the biphenyl skeleton were investigated. It was observed that the amount of residual PCBs was 1–48% of the original PCBs after three weeks of incubation. Identified metabolites indicate that the used bacterial strain attacks the biphenyl skeleton at the 2,3- and 3,4-positions, and it is also able to dehalogenate PCBs. Metabolic pathways of degradation of individual congeners were proposed. Transformation of 2,4- and 2,5-dichlorobenzoic acids by Pseudomonas sp. 2 was also observed. Metabolic pathways of polychlorinated biphenyls degradation by Pseudomonas sp. 2 Komancová et al., 2003 Link
This review summarizes our present knowledge concerning bacterial PCB oxidative catabolic pathways. Using, as an example, some of the results that were obtained mainly with Comamonas testosteroni B-356, some of the major features of PCB catabolic pathways will be depicted. Based on our present knowledge, some of the factors that should be considered in priority when looking for strategies to obtain new strains with enhanced capabilities to degrade those persistent pollutants will be discussed. The major features that will be discussed include the bioavailability of PCB as substrate, the use of co-substrate, the significance of the substrate reactivity pattern of the biphenyl oxygenase (the first enzyme of the pathway) and the importance of the stringent control of metabolite production. Biphenyl/Chlorobiphenyls catabolic pathway of Comamonas testosteroni B-356: Prospect for use in bioremediation Sylvestre. 1995 Link
In situ treatment of PCB contaminated sediments via microbial dechlorination is a promising alternative to dredging, which may be reserved for only the most contaminated areas. Reductive dechlorination of low levels of weathered PCB mixtures typical of urban environments may occur at slow rates. Here, we report that biostimulation and bioaugmentation enhanced dechlorination of low concentration (2.1 mg PCBs/kg dry weight) historical PCBs in microcosms prepared with Anacostia River, Washington, DC, sediment. Treatments included electron donors butyrate, lactate, propionate and acetate (1 mM each); alternate halogenated electron acceptors (haloprimers) tetrachlorobenzene (TeCB, 25 ?M), pentachloronitrobenzene (PCNB, 25 ?M), or 2,3,4,5,6-PCB (PCB116, 2.0 ?M); and/or bioaugmentation with a culture containing Dehalococcoides ethenogenes strain 195 (3 × 106 cells/mL). Dechlorination rates were enhanced in microcosms receiving bioaugmentation, PCNB and PCNB plus bioaugmentation, compared to other treatments. Microcosm subcultures generated after 415 days and spiked with PCB116 showed sustained capacity for dechlorination of PCB116 in PCNB, PCNB plus bioaugmentation, and TeCB treatments, relative to other treatments. Analysis of Chloroflexi 16S rRNA genes showed that TeCB and PCNB increased native Dehalococcoides spp. from the Pinellas subgroup; however this increase was correlated to enhanced dechlorination of low concentration weathered PCBs only in PCNB-amended microcosms. D. ethenogenes strain 195 was detected only in bioaugmented microcosms and decreased over 281 days. Bioaugmentation with D. ethenogenes strain 195 increased PCB dechlorination rates initially, but enhanced capacity for dechlorination of a model congener, PCB116, after 415 days occurred only in microcosms with enhanced native Dehalococcoides spp. PCB dechlorination enhancement in Anacostia River sediment microcosms Krumins et al., 2009 Link
Polychlorinated biphenyls (PCBs) are stable organic molecules that were widely used during 1930s and 1940s. Because of their widespread use, PCBs have entered the environment through both legal and illegal use and disposal and are persistent in the environment contaminating various environmental matrices worldwide. The environmental persistence of PCBs results primarily from the inability of natural aquatic and soil biota to metabolize the compound at a considerable rate. Several studies have been conducted on PCBs biodegradation to determine how the degradation rate can be improved. This paper is a review of literature and studies on the biodegradation of PCBs. Studies show that there are two biologically mediated PCBs degradation processes: anaerobic and aerobic. The anaerobic process removes chlorine atoms of highly chlorinated PCBs, which are then mineralized under aerobic condition. The degradation route is dependent on the complexity of the PCB congener coupled with the type of microorganism employed and the interaction among the microorganisms. Polychlorinated biphenyls and their biodegradation Borja et al., 2005 Link
Aerobic mineralization of PCBs, which are toxic and persistent organic pollutants, involves the upper (biphenyl, BP) and lower (benzoate, BZ) degradation pathways. The activity of different members of the soil microbial community in performing one or both pathways and their synergistic interactions during PCB biodegradation, are not well understood. This study investigates BP and BZ biodegradation and subsequent carbon flow through the microbial community in PCB-contaminated soil. DNA stable isotope probing (SIP) was used to identify the bacterial guilds involved in utilizing 13C-biphenyl (unchlorinated analogue of PCBs) and/or 13C-benzoate (product/intermediate of BP degradation and analogue of chlorobenzoates). By performing SIP with two substrates in parallel, we reveal microbes performing the upper (BP) and/or lower (BZ) degradation pathways and heterotrophic bacteria involved indirectly in processing carbon derived from these substrates (i.e. through crossfeeding). Substrate mineralization rates and shifts in relative abundance of labeled taxa suggest that BP and BZ biotransformations were performed by microorganisms with different growth strategies: BZ-associated bacteria were fast growing, potentially copiotrophic organisms, while microbes that transform BP were oligotrophic, slower growing, organisms. Our findings provide novel insight into the functional interactions of soil bacteria active in processing biphenyl and related aromatic compounds in soil, revealing how carbon flows through a bacterial community. Synergistic Processing of Biphenyl and Benzoate: Carbon Flow Through the Bacterial Community in Polychlorinated-Biphenyl-Contaminated Soil Leewis et al., 2016 Link
Polychlorinated biphenyls (PCBs) are typical lasting organic pollutants. Persistence and recalcitrance to biodegradation of PCBs have hampered the transformation of PCB congeners from the environment. Biological transformation of polychlorinated biphenyls could take place through anaerobic dechlorination, aerobic microbial degradation, and a combination of transformation of anaerobic dechlorination and aerobic degradation. Under anaerobic conditions, microbial dechlorination is an important degradation mode for PCBs, especially high-chlorinated congeners. The low-chlorinated compounds formed after reductive dechlorination could be further aerobically degraded and completely mineralized. This paper reviews the recent advances in biological degradation of PCBs, introduces the functional bacteria and enzymes involved in the anaerobic and aerobic degradation of PCBs, and discusses the synergistic action of anaerobic reduction and aerobic degradation. In addition, the different ways to the microbial remediation of PCBs-contaminated environments are discussed. This review provides a theoretical foundation and practical basis to use PCBs-degrading microorganisms for bioremediation. Recent advances in the biodegradation of polychlorinated biphenyls Xiang et al., 2020 Link