Compound degraded:Pentachlorobenzene
General Description (About POP compound)
Pentachlorobenzene (PeCB) is a chlorinated aromatic hydrocarbon. It consists of a benzene ring substituted with five chlorine atoms. PeCB was once used industrially for a variety of uses such as an intermediate in the manufacture of pesticides, particularly the fungicide pentachloronitrobenzene, a component of a mixture of chlorobenzenes added to products containing polychlorinated biphenyls in order to reduce viscosity, and as a fire retardant.
Biodegradation pathway
Publications
| Abstract | Title | Authors | Article Link |
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| Hexachlorobenzene (HCB), pentachlorobenzene (QCB), all three isomers of tetrachlorobenzene (TeCB), 1,2,3-trichlorobenzene (1,2,3-TCB), and 1,2,4-TCB were reductively dechlorinated by enrichment cultures in the presence of lactate, glucose, ethanol, or isopropanol as the electron donor. The enrichment cultures originated from percolation columns filled with Rhine River sediment in which dechlorination of TCBs and dichlorobenzenes (DCBs) occurred. A stable consortium obtained by transfer on lactate as the energy and carbon source in the presence of 1,2,3-TCB dechlorinated this isomer stoichiometrically to 1,3-DCB. Dechlorinating activity could only be maintained when an electron donor was added. Lactate, ethanol, and hydrogen appeared to be the best substrates. Optimal temperature and pH for dechlorination were 30 degrees C and 7.2, respectively. The specificity of the enrichment on lactate and 1,2,3-TCB was tested after approximately 60 transfers (after 2.5 years). HCB and QCB were stoichiometrically dechlorinated to 1,3,5-TCB and minor amounts of 1,2,4-TCB. 1,3,5-TCB was the sole product formed from 1,2,3,5-TeCB, while 1,2,3,4-TeCB and 1,2,4,5-TeCB were converted to 1,2,4-TCB. 1,2,4-TCB, 1,3,5-TCB, and the three isomers of DCB were not dechlorinated during 4 weeks of incubation. For further enrichment of the 1,2,3-TCB-dechlorinating bacteria, a two-liquid-phase (hexadecane-water) system was used with hydrogen as the electron donor and 1,2,3-TCB or CO2 as the electron acceptor. Methanogens and acetogens were the major substrate-competing (H2-CO2) microorganisms in the two-liquid-phase system. Inhibition of methanogenesis by 2-bromoethanesulfonic acid did not influence dechlorination, and acetogens which were isolated from the enrichment culture did not have dechlorinating activity.(ABSTRACT TRUNCATED AT 250 WORDS) | Enrichment and properties of an anaerobic mixed culture reductively dechlorinating 1,2,3-trichlorobenzene to 1,3-dichlorobenzene. | Holliger et al., 1992 | Link |
| Halogenated aromatics are used widely in various industrial, agricultural and household applications. However, due to their stability, most of these compounds persist for a long time, leading to accumulation in the environment. Biological degradation of halogenated aromatics provides sustainable, low?cost and environmentally friendly technologies for removing these toxicants from the environment. This minireview discusses the molecular mechanisms of the enzymatic reactions for degrading halogenated aromatics which naturally occur in various microorganisms. In general, the biodegradation process (especially for aerobic degradation) can be divided into three main steps: upper, middle and lower metabolic pathways which successively convert the toxic halogenated aromatics to common metabolites in cells. The most difficult step in the degradation of halogenated aromatics is the dehalogenation step in the middle pathway. Although a variety of enzymes are involved in the degradation of halogenated aromatics, these various pathways all share the common feature of eventually generating metabolites for utilizing in the energy?producing metabolic pathways in cells. An in?depth understanding of how microbes employ various enzymes in biodegradation can lead to the development of new biotechnologies via enzyme/cell/metabolic engineering or synthetic biology for sustainable biodegradation processes. | Microbial degradation of halogenated aromatics: molecular mechanisms and enzymatic reactions | Pimviriyakul et al., 2020 | Link |
| Hexachlorobenzene was dechlorinated to tri- and dichlorobenzenes in anaerobic sewage sludge. The complete biotransformation of 190 microM hexachlorobenzene (approximately 50 ppm) occurred within 3 weeks. The calculated rate of hexachlorobenzene dechlorination was 13.6 mumol liter-1 day-1. Hexachlorobenzene was dechlorinated via two routes, both involving the sequential removal of chlorine from the aromatic ring. The major route was hexachlorobenzene----pentachlorobenzene----1,2,3,5-tetrachlorobenzene--- -1,3,5- trichlorobenzene. Greater than 90% of the added hexachlorobenzene was recovered as 1,3,5-trichlorobenzene, and there was no evidence for further dechlorination of 1,3,5-trichlorobenzene. The minor route was hexachlorobenzene----pentachlorobenzene----1,2,4,5-tetrachlorobenzene--- -1,2,4- trichlorobenzene----dichlorobenzenes. These results extend reductive dechlorination to poorly water soluble aromatic hydrocarbons which could potentially include other important environmental pollutants like polychlorinated biphenyls. | Reductive dechlorination of hexachlorobenzene to tri- and dichlorobenzenes in anaerobic sewage sludge. | Fathepure et al., 1988 | Link |
| Aiming to comprehensively survey the potential pollution of an alpine cryoconite (Jamtalferner glacier, Austria), and its bacterial community structure along with its biodegrading potential, first chemical analyses of persistent organic pollutants, explicitly polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) as well as polycyclic aromatic hydrocarbons (PAHs), revealed a significant contamination. In total, 18 PCB congeners were detected by high resolution gas chromatography/mass spectrometry with a mean concentration of 0.8 ng/g dry weight; 16 PAHs with an average concentration of 1,400 ng/g; and 26 out of 29 OCPs with a mean concentration of 2.4 ng/g. Second, the microbial composition was studied using 16S amplicon sequencing. The analysis revealed high abundances of Proteobacteria (66%), the majority representing ?-Proteobacteria (87%); as well as Cyanobacteria (32%), however high diversity was due to 11 low abundant phyla comprising 75 genera. Biodegrading potential of cryoconite bacteria was further analyzed using enrichment cultures (microcosms) with PCB mixture Aroclor 1242. 16S rDNA analysis taxonomically classified 37 different biofilm-forming and PCB-degrading bacteria, represented by Pseudomonas, Shigella, Subtercola, Chitinophaga, and Janthinobacterium species. Overall, the combination of culture-dependent and culture-independent methods identified degrading bacteria that can be potential candidates to develop novel bioremediation strategies. | Polychlorinated Biphenyl (PCB)-Degrading Potential of Microbes Present in a Cryoconite of Jamtalferner Glacier | Weiland-Bräuer et al., 2017 | Link |
| Dechlorination patterns of three tetrachlorobenzene isomers, 1,2,3,4-, 1,2,3,5-, and 1,2,4,5-TeCB, were studied in anoxic microcosms derived from contaminated harbor sludge. The removal of doubly, singly, and un-flanked chlorine atoms was noted in 1,2,3,4- and 1,2,3,5-TeCB fed microcosms, whereas only singly flanked chlorine was removed in 1,2,4,5-TeCB microcosms. The thermodynamically more favorable reactions were selectively followed by the enriched cultures with di- and/or mono-chlorobenzene as the main end products of the reductive dechlorination of all three isomers. Based on quantitative PCR analysis targeting 16S rRNA genes of known organohalide-respiring bacteria, the growth of Dehalococcoides was found to be associated with the reductive dechlorination of all three isomers, while growth of Dehalobacter, another known TeCB dechlorinator, was only observed in one 1,2,3,5-TeCB enriched microcosm among biological triplicates. Numbers of Desulfitobacterium and Geobacter as facultative dechlorinators were rather stable suggesting that they were not (directly) involved in the observed TeCB dechlorination. Bacterial community profiling suggested bacteria belonging to the phylum Bacteroidetes and the order Clostridiales as well as sulfate-reducing members of the class Deltaproteobacteria as putative stimulating guilds that provide electron donor and/or organic cofactors to fastidious dechlorinators. Our results provide a better understanding of thermodynamically preferred TeCB dechlorinating pathways in harbor environments and microbial guilds enriched and active in anoxic TeCB dechlorinating microcosms. | Dechlorination of three tetrachlorobenzene isomers by contaminated harbor sludge-derived enrichment cultures follows thermodynamically favorable reactions | Lu et al., 2017 | Link |
| We sought to elucidate the mechanisms underlying the aerobic dechlorination of the persistent organic pollutants hexachlorobenzene (HCB) and pentachlorophenol (PCP). We performed genomic and heterologous expression analyses of dehalogenase genes in Nocardioides sp. PD653, the first bacterium found to be capable of mineralizing HCB via PCP under aerobic conditions. The hcbA1A2A3 and hcbB1B2B3 genes, which were involved in catalysing the aerobic dechlorination of HCB and PCP, respectively, were identified and characterized; they were classified as members of the two-component flavin-diffusible monooxygenase family. This was subsequently verified by biochemical analysis; aerobic dechlorination activity was successfully reconstituted in vitro in the presence of flavin, NADH, the flavin reductase HcbA3, and the HCB monooxygenase HcbA1. These findings will contribute to the implementation of in situ bioremediation of HCB- or PCP-contaminated sites, as well as to a better understanding of bacterial evolution apropos their ability to degrade heavily chlorinated anthropogenic compounds under aerobic conditions. | Mechanisms of aerobic dechlorination of hexachlorobenzene and pentachlorophenol by Nocardioides sp. PD653 | Ito. 2021 | Link |
| Anaerobic microbial dechlorination is an important step in the detoxification and elimination of polychlorinated biphenyls (PCBs), but a microorganism capable of coupling its growth to PCB dechlorination has not been isolated. Here we describe the isolation from sediment of an ultramicrobacterium, strain DF-1, which is capable of dechlorinating PCBs containing double-flanked chlorines added as single congeners or as Aroclor 1260 in contaminated soil. The isolate requires Desulfovibrio spp. in coculture or cell extract for growth on hydrogen and PCB in mineral medium. This is the first microorganism in pure culture demonstrated to grow by dehalorespiration with PCBs and the first isolate shown to dechlorinate weathered commercial mixtures of PCBs in historically contaminated sediments. The ability of this isolate to grow on PCBs in contaminated sediments represents a significant breakthrough for the development of in situ treatment strategies for this class of persistent organic pollutants. | Dehalorespiration with Polychlorinated Biphenyls by an Anaerobic Ultramicrobacterium? | May et al., 2008 | Link |
| Dehalobacter sp. strain TeCB1 was isolated from groundwater near Sydney, Australia, that is polluted with a range of organochlorines. The isolated strain is able to grow by reductive dechlorination of 1,2,4,5-tetrachlorobenzene to 1,3- and 1,4-dichlorobenzene with 1,2,4-trichlorobenzene being the intermediate daughter product. Transient production of 1,2-dichlorobenzene was detected with subsequent conversion to monochlorobenzene. The dehalogenation capability of strain TeCB1 to respire 23 alternative organochlorines was examined and shown to be limited to the use of 1,2,4,5-tetrachlorobenzene and 1,2,4-trichlorobenzene. Growth on 1,2,4-trichlorobenzene resulted in the production of predominantly 1,3- and 1,4-dichlorobenzene. The inability of strain TeCB1 to grow on 1,2-dichlorobenzene indicated that the production of monochlorobenzene during growth on 1,2,4,5-tetarchlorobezene was cometabolic. The annotated genome of strain TeCB1 contained only one detectable 16S rRNA gene copy and genes for 23 full-length and one truncated Reductive Dehalogenase (RDase) homologs, five unique to strain TeCB1. Identification and functional characterization of the 1,2,4,5-tetrachlorobenzene and 1,2,4-trichlorobenzene RDase (TcbA) was achieved using native-PAGE coupled with liquid chromatography tandem mass spectrometry. Interestingly, TcbA showed higher amino acid identity with tetrachloroethene reductases PceA (95% identity) from Dehalobacter restrictus PER-K23 and Desulfitobacterium hafniense Y51 than with the only other chlorinated benzene reductase [i.e., CbrA (30% identity)] functionally characterized to date. | Isolation and Characterization of Dehalobacter sp. Strain TeCB1 Including Identification of TcbA: A Novel Tetra- and Trichlorobenzene Reductive Dehalogenase | Alfán-Guzmán et al., 2017 | Link |
| Two Pseudomonas sp. strains, capable of growth on chlorinated benzenes as the sole source of carbon and energy, were isolated by selective enrichment from soil samples of an industrial waste deposit. Strain PS12 grew on monochlorobenzene, all three isomeric dichlorobenzenes, and 1,2,4-trichlorobenzene (1,2,4-TCB). Strain PS14 additionally used 1,2,4,5-tetrachlorobenzene (1,2,4,5-TeCB). During growth on these compounds both strains released stoichiometric amounts of chloride ions. The first steps of the catabolism of 1,2,4-TCB and 1,2,4,5-TeCB proceeded via dioxygenation of the aromatic nuclei and furnished 3,4,6-trichlorocatechol. The intermediary cis-3,4,6-trichloro-1,2-dihydroxycyclohexa-3,5-diene (TCB dihydrodiol) formed from 1,2,4-TCB was rearomatized by an NAD+-dependent dihydrodiol dehydrogenase activity, while in the case of 1,2,4,5-TeCB oxidation the catechol was obviously produced by spontaneous elimination of hydrogen chloride from the initially formed 1,3,4,6-tetrachloro-1,2-dihydroxycyclohexa-3,5-diene. Subsequent ortho cleavage was catalyzed by a type II catechol 1,2-dioxygenase producing the corresponding 2,3,5-trichloromuconate which was channeled into the tricarboxylic acid pathway via an ordinary degradation sequence, which in the present case included 2-chloro-3-oxoadipate. From the structure-related compound 2,4,5-trichloronitrobenzene the nitro group was released as nitrite, leaving the above metabolite as 3,4,6-trichlorocatechol. Enzyme activities for the oxidation of chlorobenzenes and halogenated metabolites were induced by both strains during growth on these haloaromatics and, to a considerable extent, during growth of strain PS12 on acetate. | Degradation of 1,2,4-Trichloro- and 1,2,4,5-Tetrachlorobenzene by Pseudomonas Strains | Sander et al., 1991 | Link |