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At least 19 recordsLinked to original sources

PubMed2005

3-chloro-, 2,3- and 3,5-dichlorobenzoate co-metabolism in a 2-chlorobenzoate-degrading consortium: role of 3,5-dichlorobenzoate as antagonist of 2-chlorobenzoate degradation. Metabolism and co-metabolism of chlorobenzoates.

A study was made of the metabolic and co-metabolic intermediates of 2- and 3-chlorobenzoate, 2,3- and 3,5-dichlorobenzoate to elucidate the mechanism(s) involved in the negative effects observed on the growth of a chlorobenzoate-degrading microbial consortium in the presence of mixed chlorobenzoates. 2-Chloromuconate accumulated as the end-product in the cultural broths of the microbial consortium during growth on 2-chlorobenzoate; the same 2-chloromuconate was identified in the reaction mixtures of resting cells pregrown on 2-chlorobenzoate and exposed to 3-chloro- and 2,3-dichlorobenzoate, while in similar experiments 1,2-dihydroxy-3,5-dichloro-cyclohexa-3,5-dienoate was detected as dead-end product of 3,5-dichlorobenzoate co-metabolism. These results suggest an initial degradative attack by 2-chlorobenzoate induced dioxygenase(s). The role of 3,5-dichlorobenzoate as an antagonist of 2-chlorobenzoate degradation was also studied: in the presence of mixed 2-chloro- and 3,5-dichlorobenzoate, the 3,5-dichlorobenzoate preferential uptake by the resting cells of the chlorobenzoate-degrading consortium was observed. 2-Chlorobenzoate entered the cells only after the complete removal of the co-substrate. In growing cells experiments, the addition of 1,2-dihydroxy-3,5-dichloro-cyclohexa-3,5-dienoate, the 3,5-dichlorobenzoate co-metabolite, to 2-chlorobenzoate exerted the same antagonistic effect of the parent compound, inhibiting both the microbial growth and the degradative process. These data are discussed, allowing us to attribute the inhibitory effects observed to a substrate/co-substrate competition, though other additional causes may not be totally excluded.

Bacteria↗

PubMed1991

Dehalogenation of 4-chlorobenzoate by 4-chlorobenzoate dehalogenase from pseudomonas sp. CBS3: an ATP/coenzyme A dependent reaction.

Pseudomonas sp. CBS3 was grown with 4-chlorobenzoate as sole source of carbon and energy. Freshly prepared cell-free extracts converted 4-chlorobenzoate to 4-hydroxybenzoate. After storage for 16 hours at 25 degrees C only about 50% of the initial activity was left. Treatment at 55 degrees C for 10 minutes, dialysis or desalting of the extracts by gel filtration caused a total loss of the activity of the 4-chlorobenzoate dehalogenase. The activity could be restored by the addition of ATP, coenzyme A and Mg2+. If one of these cofactors was missing, no dehalogenating activity was detectable. The amount of 4-hydroxybenzoate formed was proportional to the amount of ATP available in the test system whereas CoA served as a real coenzyme. A novel ATP/coenzyme A dependent reaction mechanism for the dehalogenation of 4-chlorobenzoate by 4-chlorobenzoate dehalogenase from Pseudomonas sp. CBS3 is proposed.

Adenosine Triphosphate↗

PubMed2001

The chlorobenzoate dioxygenase genes of Burkholderia sp. strain NK8 involved in the catabolism of chlorobenzoates.

Burkholderia sp. NK8 grows abundantly on 3-chlorobenzoate (3CB),4-chlorobenzoate (4CB) and benzoate. The genes encoding the oxidation of (chloro)benzoates (cbeABCD) and catechol (catA, catBC), the LysR-type regulatory gene cbeR and the gene cbeE with unknown function, all of which form a single cluster in NK8, were cloned and analysed. The protein sequence of chlorobenzoate 1,2-dioxygenase (CbeABC) is 50-65% identical to the benzoate dioxygenase (BenABC) of Acinetobacter sp. ADP1, toluate dioxygenase (XylXYZ) of the TOL plasmid pWW0 and 2-halobenzoate dioxygenase (CbdABC) of Burkholderia cepacia 2CBS. Disruption of the cbeA gene resulted in the simultaneous loss of the ability to grow on benzoate and monochlorobenzoates, indicating the involvement of the cbeABCD genes in the degradation of these aromatics. The cbeABCD genes are preceded by catA, the gene for catechol dioxygenase. lacZ transcriptional fusion studies in Pseudomonas putida showed that catA and cbeA are co-expressed under the positive control of cbeR, a LysR-type transcriptional regulatory gene. The cbeA::lacZ transcriptional fusion studies showed that the inducers of the genes are 3CB, 4CB, benzoate and probably cis,cis-muconate. On the other hand, 2-chlorobenzoate (2CB) did not activate the expression of the genes. The chlorobenzoate dioxygenase was able to transform 2CB, 3CB, 4CB and benzoate at considerable rates. 2CB yielded both catechol and 3-chlorocatechol (3CC), and 3CB gave rise to 4-chlorocatechol and 3CC as the major and minor intermediate products, respectively, indicating that the NK8 dioxygenase lacks absolute regiospecificity. The absence of growth of NK8 on 2CB, despite its considerable degradation activity against 2CB, is apparently due to the inability of CbeR to recognize 2CB as an inducer of the expression of the cbe genes.

Bacterial Proteins↗

PubMed2001

The chlorocatechol degradative genes, tfdT-CDEF, of Burkholderia sp. strain NK8 are involved in chlorobenzoate degradation and induced by chlorobenzoates and chlorocatechols.

The modified-ortho pathway genes responsible for the degradation of chlorocatechols produced from 3- and 4-chlorobenzoate in Burkholderia sp. NK8 were cloned and analyzed. The five genes predicted to encode a LysR-type transcriptional regulator, chlorocatechol 1,2-dioxygenase, chloromuconate cycloisomerase, dienelactone hydrolase, and maleylacetate reductase were designated tfdT, tfdC, tfdD, tfdE, and tfdF, respectively since they show the highest similarity to the corresponding genes of the chlorocatechol degradation gene cluster (tfdT-CDEF) of 2,4-dichlorophenoxyacetic acid degrading plasmid pJP4 from Ralstonia eutropha JMP134 (79-88% amino acid identity). TfdC of NK8 showed the highest activity against 3,5-dichlorocatechol in all kinds of chlorocatechols tested, which is a characteristic of TfdC of pJP4. By reporter gene (lacZ) analysis, tfdT of NK8 was shown to activate the transcription from the tfdC promoter. Unlike the regulators of other chlorocatechol degradation genes so far reported, 2-chlorobenzoate, 3-chlorobenzoate, 3-chlorocatechol and 4-chlorocatechol, were shown to act as effectors of TfdT.

Amino Acid Sequence↗

PubMed1996

Influence of chlorobenzoates on the utilisation of chlorobiphenyls and chlorobenzoate mixtures by chlorobiphenyl/chlorobenzoate-mineralising hybrid bacterial strains.

Chlorobenzoates (CBA) arise as intermediates during the degradation of polychlorinated biphenyls (PCBs) and some chlorinated herbicides. Since PCBs were produced as complex mixtures, a range of mono-, di-, and possibly trichloro-substituted benzoates would be formed. Chlorobenzoate degradation has been proposed to be one of the rate-limiting steps in the overall PCB-degradation process. Three hybrid bacteria constructed to have the ability to completely mineralise 2-, 3-, or 4-monochlorobiphenyl respectively, have been studied to establish the range of mono- and diCBAs that can be utilised. The three strains were able to mineralise one or more of the following CBAs: 2-, 3-, and 4-monochlorobenzoate and 3,5-dichlorobenzoate. No utilisation of 2,3-, 2,5-, 2,6-, or 3,4-diCBA was observed, and only a low concentration (0.11 mM) of 2,4-diCBA was mineralised. When the strain with the widest substrate range (Burkholderia cepacia JHR22) was simultaneously supplied with two CBAs, one that it could utilise plus one that it was unable to utilise, inhibitory effects were observed. The utilisation of 2-CBA (2.5 mM) by this strain was inhibited by 2,3-CBA (200 microM) and 3,4-CBA (50 microM). Although 2,5-cba and 2,6-cba were not utilised as carbon sources by strain jhr22, they did not inhibit 2-cba utilisation at the concentrations studied, whereas 2,4-cba was co-metabolised with 2-cba. The utilisation of 2-, 3-, and 4-chlorobiphenyl by strain JHR22 was also inhibited by the presence of 2,3- or 3,4-diCBA. We conclude that the effect of the formation of toxic intermediates is an important consideration when designing remediation strategies.

Biodegradation, Environmental↗

PubMed2004

Chlorobenzoate-degrading bacteria in similar pristine soils exhibit different community structures and population dynamics in response to anthropogenic 2-, 3-, and 4-chlorobenzoate levels.

A study was conducted to determine the diversity of 2-, 3-, and 4-chlorobenzoate (CB) degraders in two pristine soils with similar physical and chemical characteristics. Surface soils were collected from forested sites and amended with 500 microg of 2-, 3-, or 4-CB g(-1) soil. The CB levels and degrader numbers were monitored throughout the study. Degraders were isolated, grouped by DNA fingerprints, identified via 16S rDNA sequences, and screened for plasmids. The CB genes in selected degraders were isolated and/or sequenced. In the Madera soil, 2-CB and 4-CB degraded within 11 and 42 d, respectively, but 3-CB did not degrade. In contrast, 3-CB and 4-CB degraded in the Oversite soil within 14 and 28 d, respectively, while 2-CB did not degrade. Approximately 10(7) CFU g(-1) of degraders were detected in the Madera soil with 2-CB, and the Oversite soil with 3- and 4-CB. No degraders were detected in the Madera soil with 4-CB even though the 4-CB degraded. Nearly all of the 2-CB degraders isolated from the Madera soil were identified as a Burkholderia sp. containing chromosomally encoded degradative genes. In contrast, several different 3- and 4-CB degraders were isolated from the Oversite soil, and their populations changed as CB degradation progressed. Most of these 3-CB degraders were identified as Burkholderia spp. while the majority of 4-CB degraders were identified as Bradyrhizobium spp. Several of the 3-CB degraders contained the degradative genes on large plasmids, and there was variation between the plasmids in different isolates. When a fresh sample of Madera soil was amended with 50, 100, or 200 microg 3-CB g(-1), 3-CB degradation occurred, suggesting that 500 microg 3-CB g(-1) was toxic to the degraders. Also, different 3-CB degraders were isolated from the Madera soil at each of the three lower levels of 3-CB. No 2-CB degradation was detected in the Oversite soil even at lower 2-CB levels. These results indicate that the development of 2-, 3-, and 4-CB degrader populations is site-specific and that 2-, 3-, and 4-CB are degraded by different bacterial populations in pristine soils. These results also imply that the microbial ecology of two soils that develop under similar biotic and abiotic environments can be quite different.

Arizona↗

PubMed1997

Reduction of 3-chlorobenzoate, 3-bromobenzoate, and benzoate to corresponding alcohols by Desulfomicrobium escambiense, isolated from a 3-chlorobenzoate-dechlorinating coculture.

An anaerobic bacterial coculture which dechlorinated 3-chlorobenzoate (3CB) to benzoate was obtained by single-colony isolation from an anaerobic bacterial consortium which completely degraded 3CB in defined medium. Of 29 additional halogenated aromatic compounds tested, the coculture removed the meta halogen from 2,3- and 2,5-dichlorobenzoate, 3-bromobenzoate (3BB), 5-chlorovanillate (5CV), and 3-chloro-4-hydroxybenzoate. Dechlorinating activity in the coculture required the presence of pyruvate. 5CV was also O-demethoxylated. The coculture contained two cell types: a short, straight gram-negative rod and a long, thin, curved gram-positive rod. The short rod, Desulfomicrobium escambiense, was recently isolated and identified as a new sulfate-reducing bacterial species (B. R. Sharak Genthner, S. D. Friedman, and R. Devereux, Int. J. Syst. Bacteriol. 47:889-892, 1997; B. R. Sharak Genthner, G. Mundfrom, and R. Devereux, Arch. Microbiol. 161:215-219, 1994). D. escambiense did not dehalogenate any of the compounds dehalogenated by the coculture, nor dit it O-demethoxylate 5CV or vanillate. However, D. escambiense reduced 3CB, EBB, and benzoate to their respective benzyl alcohols. Reduction to alcohols required the presence of pyruvate, which was transformed to acetate, lactate, and succinate in the presence of absence of 3CB, 3BB, or benzoate. Alcohol formation did not occur in pyruvate-sulfate medium. Under these conditions, sulfate was preferentially reduced. Other electron donors that supported the growth of D. escambiense during sulfate reduction did not support benzoate reduction to benzyl alcohol.

Benzoates↗

PubMed2004

Functional establishment of introduced chlorobenzoate degraders following bioaugmentation with newly activated soil. Enhanced contaminant remediation via activated soil bioaugmentation.

Introduced degraders often do not survive when applied to polluted sites; however, the potential for successful bioaugmentation may be increased if newly activated soil (containing indigenous degrader populations recently exposed to the contaminant) or potentially active soil (containing indigenous degrader populations not previously exposed to the contaminant) is used as the inoculant. To investigate this concept, Madera and Oversite soils were amended with 0 or 500 micrograms of 2-, 3-, or 4-chlorobenzoate per gram soil. The Madera degraded 2-chlorobenzoate while the Oversite degraded 3- and 4-chlorobenzoate. After 22 days of incubation, non-active soils that had not degraded chlorobenzoate were bioaugmented with the appropriate activated soil that had been exposed to and degraded chlorobenzoate. Thus, Oversite soil that had not degraded 2-chlorobenzoate was bioaugmented with Madera soil that had degraded 2-chlorobenzoate. Likewise, Madera soil that had not degraded 3- or 4-chlorobenzoate was bioaugmented with the Oversite soil that had degraded 3- or 4-chlorobenzoate. Additionally, the non-active soils were bioaugmented with the corresponding potentially active soils. The Oversite soil amended with activated Madera soil degraded the 2-chlorobenzoate within 3 days of bioaugmentation. The Madera soil amended with activated Oversite soils degraded the 3- and 4-chlorobenzoate within 20 and 6 days, respectively. Large degrader populations developed in microcosms bioaugmented with activated soil, and shifts in the 3- and 4-CB degrader community structures occurred following bioaugmentation. In contrast, bioaugmentation with potentially active soil did not impact degradation. The results indicate the potential for bioaugmentation with newly activated soil to enhance contaminant degradation.

Biodegradation, Environmental↗

PubMed2001

Soil microbial population dynamics following bioaugmentation with a 3-chlorobenzoate-degrading bacterial culture. Bioaugmentation effects on soil microorganisms.

Changes in microbial populations were evaluated following inoculation of contaminated soil with a 3-chlorobenzoate degrader. Madera sandy loam was amended with 0, 500, or 1,000 microg 3-chlorobenzoate g(-1) dry soil. Selected microcosms were inoculated with the degrader Comamonas testosteroni BR60. Culturable bacterial degraders were enumerated on minimal salts media containing 3-chlorobenzoate. Culturable heterotrophic bacteria were enumerated on R2A. Isolated degraders were grouped by enterobacterial repetitive intergenic consensus sequence-polymerase chain reaction fingerprints and identified based on 16S ribosomal-DNA sequences. Bioaugmentation increased the rate of degradation at both levels of 3-chlorobenzoate. In both the 500 and 1,000 microg 3-chlorobenzoate g(-1) dry soil inoculated microcosms, degraders increased from the initial inoculum and decreased following degradation of 3-CB. Inoculation delayed the development of indigenous 3-chlorobenzoate degrading populations. It is unclear if inoculation altered the composition of indigenous degrader populations. In the uninoculated soil, degraders increased from undetectable levels to 6.6 x 10(7) colony-forming-units g(-1) dry soil in the 500 microg 3-chlorobenzoate g(-1) dry soil microcosms, but none were detected in the 1,000 microg 3-chlorobenzoate g(-1) dry soil microcosms. Degraders isolated from uninoculated soil were identified as one of two distinct Burkholderia species. In the uninoculated soil, numbers of culturable heterotrophic bacteria initially decreased following addition of 1,000 microg 3-chlorobenzoate g(-1) dry soil. Inoculation with C. testosteroni reduced this negative impact on culturable bacterial numbers. The results indicate that bioaugmentation may not only increase the rate of 3-chlorobenzoate degradation but also reduce the deleterious effects of 3-chlorbenzoate on indigenous soil microbial populations.

Biodegradation, Environmental↗

PubMed2002

Community shifts in a seeded 3-chlorobenzoate degrading membrane biofilm reactor: indications for involvement of in situ horizontal transfer of the clc-element from inoculum to contaminant bacteria.

Pseudomonas putida BN210, carrying the self- transferable clc-element encoding degradation of 3-chlorobenzoate on the chromosome, was used as inoculum in different membrane biofilm reactors treating 3-chlorobenzoate-contaminated model wastewater. Analysis of the bacterial population in the effluent and in the biofilm showed the loss of BN210 beyond detection from the reactors and the appearance of several novel 3-chlorobenzoate mineralizing bacteria mainly belonging to the beta-proteobacteria. In contrast, in non-inoculated reactors, no 3-chlorobenzoate degradation was observed and no 3-chlorobenzoate degraders could be recovered. Southern blots hybridization of genomic DNA using clc-element-specific probes and FIGE analysis indicated the presence of the complete clc-element in one or more copies in the isolates. Moreover, the isolates could transfer the clc genes to Ralstonia metallidurans recipients. Two representative reactor isolates, Ralstonia sp. strains KP3 and KP9 demonstrated a higher growth rate on 3-chlorobenzoate than strain BN210 in batch cultures. When BN210, KP3 and KP9 were simultaneously inoculated in a membrane reactor supplied with 3-chlorobenzoate, strain KP3 outcompeted the two other strains and remained the major 3-chlorobenzoate degrading population in the reactor. Our data suggest that in situ horizontal transfer of the clc-element from the inoculum to contaminant bacteria in the reactors was involved in the establishment of novel 3-chlorobenzoate degrading populations that were more competitive under the defined reactor conditions than the inoculum strain.

Biodegradation, Environmental↗

PubMed1989

Degradation of 2-chlorobenzoate by Pseudomonas cepacia 2CBS.

A bacterium was isolated from water by enrichment on 2-chlorobenzoate as sole source of carbon and energy. Based on morphological and physiological properties, this microorganism was assigned to the species Pseudomonas cepacia. The organism was designated Pseudomonas cepacia 2CBS. During growth on 2-chlorobenzoate, the chlorine substituent was released quantitatively, and a small amount of 2,3-dihydroxybenzoate accumulated in the culture medium. Mutants of Pseudomonas cepacia 2CBS were induced by treatment with N-methyl-N'-nitro-N-nitrosoguanidine. Some of these mutants produced catechol from 2-chlorobenzoate. Other mutants accumulated the meta-cleavage product of catechol, 2-hydroxy-cis,cis-muconic acid semialdehyde. In crude cell-free extracts of Pseudomonas cepacia 2CBS, an enzyme was detected which catalysed the conversion of 2-chlorobenzoate to catechol. Molecular oxygen, NADH and exogenous Fe2+ were required for activity. Stoichiometric amounts of chloride were released. Experiments with 18O2 revealed that both oxygen atoms in the hydroxyl groups of the product were derived from molecular oxygen. Thus, the enzyme catalysing the conversion of 2-chlorobenzoate was identified as 2-chlorobenzoate 1,2-dioxygenase (1,2-hydroxylating, dehalogenating, decarboxylating). 2-Chlorobenzoate 1,2-dioxygenase from Pseudomonas cepacia 2CBS was shown to be a multicomponent enzyme system. The activities of catechol 2,3-dioxygenase and catechol 1,2-dioxygenase were detected in crude cell-free extracts. The activity of catechol 2,3-dioxygenase was 60 times higher than the activity of catechol 1,2-dioxygenase, indicating that catechol is mainly degraded via meta-cleavage in Pseudomonas cepacia 2CBS. No enzyme was found which converted 2,3-dihydroxybenzoate, suggesting that this compound is a dead-end metabolite of 2-chlorobenzoate catabolism. A pathway for the degradation of 2-chlorobenzoate by Pseudomonas cepacia 2CBS is proposed.

Catechols↗

PubMed1993

Enhanced mineralization of polychlorinated biphenyls in soil inoculated with chlorobenzoate-degrading bacteria.

An Altamont soil containing no measurable population of chlorobenzoate utilizers was examined for the potential to enhance polychlorinated biphenyl (PCB) mineralization by inoculation with chlorobenzoate utilizers, a biphenyl utilizer, combinations of the two physiological types, and chlorobiphenyl-mineralizing transconjugants. Biphenyl was added to all soils, and biodegradation of 14C-Aroclor 1242 was assessed by disappearance of that substance and by production of 14CO2. Mineralization of PCBs was consistently greatest (up to 25.5%) in soils inoculated with chlorobenzoate degraders alone. Mineralization was significantly lower in soils receiving all other treatments: PCB cometabolizer (10.7%); chlorobiphenyl mineralizers (8.7 and 14.9%); and mixed inocula of PCB cometabolizers and chlorobenzoate utilizers (11.4 and 18.0%). However, all inoculated soils had higher mineralization than did the uninoculated control (3.1%). PCB disappearance followed trends similar to that observed with the mineralization data, with the greatest degradation occurring in soils inoculated with the chlorobenzoate-degrading strains Pseudomonas aeruginosa JB2 and Pseudomonas putida P111 alone. While the mechanism by which the introduction of chlorobenzoate degraders alone enhanced biodegradation of PCBs could not be elucidated, the possibility that chlorobenzoate inoculants acquired the ability to metabolize biphenyl and possibly PCBs was explored. When strain JB2, which does not utilize biphenyl, was inoculated into soil containing biphenyl and Aroclor 1242, the frequency of isolates able to utilize biphenyl and 2,5-dichlorobenzoate increased progressively with time from 3.3 to 44.4% between 15 and 48 days, respectively. Since this soil contained no measurable level of chlorobenzoate utilizers yet did contain a population of biphenyl utilizers, the possibility of genetic transfer between the latter group and strain JB2 cannot be excluded.

Biodegradation, Environmental↗

PubMed2006

Effects of endogenous substrates on adaptation of anaerobic microbial communities to 3-chlorobenzoate.

Lengthy adaptation periods in laboratory studies evaluating the potential for contaminant biodegradation in natural or engineered environments may indicate that the native microbial communities are not metabolizing the contaminants in situ. In this study, we characterized the adaptation period preceding the biodegradation of 3-chlorobenzoate in anaerobic communities derived from lake sediment and wastewater sludge digesters. The importance of alternative mechanisms of adaptation of the anaerobic communities to 3-chlorobenzoate was evaluated by monitoring the concentrations of metabolic substrates and products as well as the levels of total small subunit (SSU) rRNA and SSU rRNA from populations thought to be important in 3-chlorobenzoate mineralization. The anaerobic environments from which the 3-chlorobenzoate-degrading communities were derived contained different levels of endogenous substrates. Increasing methane levels in the digester and sediment communities and decreasing chemical oxygen demand concentrations in the sediment community during the adaptation periods revealed that endogenous substrates were preferentially utilized relative to 3-chlorobenzoate. Methane and chemical oxygen demand concentrations leveled off concomitantly with the onset of 3-chlorobenzoate biodegradation, suggesting that depletion of the preferentially degraded endogenous substrates stimulated 3-chlorobenzoate metabolism. Consistent with these observations, adaptation to 3-chlorobenzoate occurred more rapidly in digester samples that were depleted of endogenous substrates compared to samples that contained high levels of these biodegradable compounds. Other potential adaptation mechanisms, e.g., genetic change or selective population enrichment, appeared to be less important based on the reproducibility and relative lengths of the adaptation events, trends in the SSU rRNA levels, and/or amplification of SSU rRNA genes from key populations.

Adaptation, Physiological↗

PubMed2002

Removal of 3-chlorobenzoate using an upflow anaerobic sludge blanket reactor under light conditions.

The possibility of 3-chlorobenzoate removal from water using an upflow anaerobic sludge blanket (UASB) reactor without the addition of any extra dechlorinating culture under light conditions has been studied on a laboratory scale. Benzoate removal was observed in the first three months of operation under light conditions, but the 3-chlorobenzoate removal was not observed. After three months of operation under light conditions, the 3-chlorobenzoate concentration in the UASB reactor effluent gradually decreased to less than 1 mg x h(-1). The 3-chlorobenzoate concentration in the effluent did not increase under dark conditions. The DOC concentration in the effluent decreased according to the removal of the 3-chlorobenzoate by the UASB granules. These results indicated that granules in the UASB reactor provided the 3-chlorobenzoate removability after 80-100 d of adaptation to the 3-chlorobenzoate, and that the UASB reactor is useful for 3-chlorobenzoate removal.

Bacteria, Anaerobic↗

PubMed1987

Growth yield increase linked to reductive dechlorination in a defined 3-chlorobenzoate degrading methanogenic coculture.

The microbially mediated reductive dehalogenation of aromatic compounds is potentially important in removal of chlorinated aromatic compounds from the environment. Thermodynamic data are presented which show that the reductive dechlorination of 3-chlorobenzoate to benzoate is exergonic, which led to the hypothesis that reductive elimination of chlorine from 3-chlorobenzoate yields biologically useful energy. In the present paper this hypothesis is tested. Experimental data were obtained with a defined 3-chlorobenzoate degrading methanogenic consortium. These data showed that (i) the molar growth yield of a defined 3-chlorobenzoate degrading consortium increased from 4.9 g protein per mol benzoate metabolized to 6.8 g protein per mol 3-chlorobenzoate when 3-chlorobenzoate replaced benzoate as energy source, and that (ii) the ATP level in starved consortium cells was twice as high when the cells were fed 3-chlorobenzoate than when fed benzoate. These observations show that the electrochemical potential between the redox partners of the H+/H2 (electron-donating) and 3-chlorobenzoate/benzoate (electron-accepting) couples is a potential source of energy and are consistent with the hypothesis that reductive dechlorination of aromatic compounds is coupled to a novel type of microbial chemotrophy.

Adenosine Triphosphate↗

PubMed2006

4-Chlorobenzoate uptake in Comamonas sp. strain DJ-12 is mediated by a tripartite ATP-independent periplasmic transporter.

The fcb gene cluster involved in the hydrolytic dehalogenation of 4-chlorobenzoate is organized in the order fcbB-fcbA-fcbT1-fcbT2-fcbT3-fcbC in Comamonas sp. strain DJ-12. The genes are operonic and inducible with 4-chloro-, 4-iodo-, and 4-bromobenzoate. The fcbT1, fcbT2, and fcbT3 genes encode a transporter in the secondary TRAP (tripartite ATP-independent periplasmic) family. An fcbT1T2T3 knockout mutant shows a much slower growth rate on 4-chlorobenzoate compared to the wild type. 4-Chlorobenzoate is transported into the wild-type strain five times faster than into the fcbT1T2T3 knockout mutant. Transport of 4-chlorobenzoate shows significant inhibition by 4-bromo-, 4-iodo-, and 4-fluorobenzoate and mild inhibition by 3-chlorobenzoate, 2-chlorobenzoate, 4-hydroxybenzoate, 3-hydroxybenzoate, and benzoate. Uptake of 4-chlorobenzoate is significantly inhibited by ionophores which collapse the proton motive force.

Adenosine Triphosphate↗

PubMed1990

Reductive dechlorination of 3-chlorobenzoate is coupled to ATP production and growth in an anaerobic bacterium, strain DCB-1.

Thermodynamic data that the reductive dechlorination of 3-chlorobenzoate is exergonic have led to the hypothesis that this reaction yields biologically useful energy. This hypothesis was tested with strain DCB-1, a dehalogenating bacterium. The organism was grown under strictly anaerobic conditions in vitamin-amended mineral medium with formate plus acetate as electron donor and 3-chlorobenzoate as electron acceptor. The cell yield increased stoichiometrically to the amount of 3-chlorobenzoate dechlorinated. No growth was observed in the absence of 3-chlorobenzoate, or when 3-chlorobenzoate was replaced by benzoate. To obtain further evidence on that energy is derived from dechlorination, 3-chlorobenzoate was added to starved cells. This amendment resulted in an increase in the ATP level of the cells at 10 nmol per mg protein versus 3 nmol per mg protein in non-amended controls. These data indicate that the reductive dehalogenation of chlorinated aromatic compounds can be coupled to a novel type of chemotrophy.

Adenosine Triphosphate↗

PubMed1988

Chlorobenzoate catabolism and interactions between Alcaligenes and Pseudomonas species from Bloody Run Creek.

A mixed community of bacteria from surface runoff waters of the Hyde Park industrial landfill was enriched on 3-chlorobenzoate. Alcaligenes and Pseudomonas species were dominant in the community. Alcaligenes sp. BR60 carried an unstable plasmid specifying 3-chlorobenzoate catabolism. Metabolites detected in culture supernatants included chlorocatechol and chloro-cis, cismuconic acid. Oxygen uptake in the presence of 3- and 4-substituted methyl-catechols revealed a catechol-1,2-oxygenase activity specific for substituted catechols with very limited activity for catechol. The isolate grew very slowly on benzoate. Alcaligenes sp. BR60 was isolated in co-culture with Pseudomonas fluorescens NR52. The latter contained no detectable plasmids and did not grow on benzoate or any of the chlorobenzoates in pure culture. Growth of the co-culture in Bloody Run Creek water supplemented with 3-chlorobenzoate indicated that phosphate concentrations in the water severely limited biodegradation. Under phosphate limited conditions in continuous culture, Pseudomonas fluorescens NR52 effectively scavenged available phosphate when it was present at a ratio of 1 cell to 20 of Alcaligenes sp. BR60. Under these conditions the growth of Alcaligenes sp. BR60 on 3-chlorobenzoate was reduced 5 fold, the frequency of plasmid deletion mutants increased, and 96% of the contaminant remained in the outflow in the form of the starting material or metabolites. No evidence was found for conjugation of the plasmid determining chlorobenzoate catabolism in Alcaligenes sp. BR60 to P. fluorescens NR52.

Alcaligenes↗