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PubMed1986

Microbial degradation of 1,3-dichlorobenzene.

A gram-negative, peritrichously flagellated rod, tentatively identified as an Alcaligenes sp., was isolated from a mixture of soil and water samples by using 1,3-dichlorobenzene as the sole carbon and energy source. During growth on 1,3-dichlorobenzene, almost stoichiometric amounts of chloride were released. Simultaneous adaptation studies, as well as enzyme studies, indicated that 1,3-dichlorobenzene was metabolized via 3,5-dichloro-cis-1,2-dihydroxycyclohexa-3,5-diene to 3,5-dichlorocatechol. Subsequently, the latter product was cleaved, yielding 2,4-dichloromuconate. No initial hydrolytic step yielding 3-chlorophenol was detected in this species.

Alcaligenes↗
PubMed1987

Transformations of chloroguaiacols, chloroveratroles, and chlorocatechols by stable consortia of anaerobic bacteria.

Metabolically stable consortia of anaerobic bacteria obtained by enrichment of sediment samples with 3,4,5-trimethoxybenzoate (TMBA), 3,4,5-trihydroxybenzoate (gallate [GA]), or 5-chlorovanillin (CV) were used to study the anaerobic transformation of a series of chloroveratroles, chloroguaiacols, and chlorocatechols used as cosubstrates. Experiments were carried out with growing cultures, and the following pathways were demonstrated for metabolism of the growth substrates: (i) TMBA produced GA, which was further degraded without the formation of aromatic intermediates; (ii) GA formed pyrogallol, which was stable to further transformation; and (iii) CV was degraded by a series of steps involving de-O-methylation, oxidation of the aldehyde group, and decarboxylation to 3-chlorocatechol before ring cleavage. Mono-de-O-methylation of the cosubstrates occurred rapidly in the order 4,5,6-trichloroguaiacol greater than 3,4,5-trichloroguaiacol approximately 3,4,5-trichloroveratrole approximately tetrachloroveratrole greater than tetrachloroguaiacol and was concomitant with degradation of the growth substrates. For the polymethoxy compounds--chloroveratroles, 1,2,3-trichloro-4,5,6-trimethoxybenzene, and 4,5,6-trichlorosyringol--de-O-methylation took place sequentially. The resulting chlorocatechols were stable to further transformation until the cultures had exhausted the growth substrates; selective dechlorination then occurred with the formation of 3,5-dichlorocatechol from 3,4,5-trichlorocatechol and of 3,4,6-trichlorocatechol from tetrachlorocatechol. 2,4,5-, 2,4,6-, and 3,4,5-trichoroanisole and 2,3,4,5-tetrachloroanisole were de-O-methylated, but the resulting chlorophenols were resistant to dechlorination. These results extend those of a previous study with spiked sediment samples and their endogenous microflora and illustrate some of the transformations of chloroguaiacols and chlorocatechols which may be expected to occur in anaerobic sediments.

Anisoles↗
PubMed1987

Degradation of 1,4-dichlorobenzene by a Pseudomonas sp.

A Pseudomonas species able to degrade p-dichlorobenzene as the sole source of carbon and energy was isolated by selective enrichment from activated sludge. The organism also grew well on chlorobenzene and benzene. Washed cells released chloride in stoichiometric amounts from o-, m-, and p-dichlorobenzene, 2,5-dichlorophenol, 4-chlorophenol, 3-chlorocatechol, 4-chlorocatechol, and 3,6-dichlorocatechol. Initial steps in the pathway for p-dichlorobenzene degradation were determined by isolation of metabolites, simultaneous adaptation studies, and assay of enzymes in cell extracts. Results indicate that p-dichlorobenzene was initially converted by a dioxygenase to 3,6-dichloro-cis-1,2-dihydroxycyclohexa-3,5-diene, which was converted to 3,6-dichlorocatechol by an NAD+-dependent dehydrogenase. Ring cleavage of 3,6-dichlorocatechol was by a 1,2-oxygenase to form 2,5-dichloro-cis, cis-muconate. Enzymes for degradation of haloaromatic compounds were induced in cells grown on chlorobenzene or p-dichlorobenzene, but not in cells grown on benzene, succinate, or yeast extract. Enzymes of the ortho pathway induced in cells grown on benzene did not attack chlorobenzenes or chlorocatechols.

Biodegradation, Environmental↗
PubMed1988

Methylation of halogenated phenols and thiophenols by cell extracts of gram-positive and gram-negative bacteria.

O-methylation of 2,6-dibromophenol was studied in cell extracts prepared from Rhodococcus sp. strain 1395. O-methylation activity was enhanced by the addition of S-adenosyl-l-methionine but was not affected by the addition of 5-methyltetrahydrofolate nor by up to 10 mM MgCl(2) or EDTA. By using 2,6-dibromophenol, 4,5,6-trichloroguaiacol, and pentachlorothiophenol as the substrates, O-methylation activity was also demonstrated in extracts from two other Rhodococcus sp. strains, an Acinetobacter sp. strain, and a Pseudomonas sp. strain. A diverse range of chloro- and bromophenols, chlorothiophenols, chloro- and bromoguaiacols, and chloro- and bromocatechols were assayed as the substrates by using extracts prepared from strain 1395; all of the compounds were methylated to the corresponding anisoles, veratroles, or guaiacols, which have been identified previously from experiments using whole cells. The specific activity of the enzyme towards the thiophenols was significantly higher than it was towards all the other substrates-high activity was found with pentafluorothiophenol, although the activity with pentafluorophenol was undetectable with the incubation times used. For the chlorophenols, the position of the substituents was of cardinal importance. The enzyme had higher activity towards the halogenated catechols than towards the corresponding guaiacols, and selective O-methylation of the 3,4,5-trihalogenocatechols yielded predominantly the 3,4,5-trihalogenoguaiacols. As in experiments with whole cells, neither 2,4-dinitrophenol, hexachlorophene, nor 5-chloro- or 5-bromovanillin was O-methylated. The results showed conclusively that the methylation reactions were enzymatic and confirmed the conclusion from extensive studies using whole cells that methylation of halogenated phenols may be a significant alternative to biodegradation.

Journal Article↗
PubMed1988

O-Methylation of Chlorinated para-Hydroquinones by Rhodococcus chlorophenolicus.

Rhodococcus chlorophenolicus PCP-I, a degrader of polychlorinated phenols, guaiacols (2-methoxyphenols), and syringols (2,6-dimethoxyphenols), was shown to O-methylate the degradation intermediate, a chlorinated para-hydroquinone, into 4-methoxyphenol. O-methylation was constitutively expressed, whereas the degradation of chlorophenols and chlorohydroquinones was inducible in R. chlorophenolicus. The O-methylating reaction required two hydroxyl groups in positions para to each other. R. chlorophenolicus selectively methylated the hydroxyl group flanked by two chlorine substituents. Tetrachlorohydroquinone, trichlorohydroquinone, and 2,6-dichlorohydroquinone were methylated into tetrachloro-4-methoxyphenol, 2,3,5-trichloro-4-methoxyphenol, and 3,5-dichloro-4-methoxyphenol, respectively. Chlorohydroquinones with only one chlorine adjacent to a hydroxyl group were methylated only in trace amounts, and no metabolite was formed from hydroquinone. The degradation intermediates formed in hydroxylation of tetrachloroguaiacol and trichlorosyringol by R. chlorophenolicus were O-methylated into two isomeric trichlorodimethoxyphenols and two isomeric dichlorotrimethoxyphenols, respectively. R. chlorophenolicus also degraded the polychlorinated methylation products (tetrachlorinated and trichlorinated 4-methoxyphenols), but not mono- and dichlorinated 4-methoxyphenols.

Journal Article↗
PubMed1989

Hydroxylation and Dechlorination of Tetrachlorohydroquinone by Rhodococcus sp. Strain CP-2 Cell Extracts.

A cell extract of a polychlorophenol-degrading bacterium, Rhodococcus sp. strain CP-2, isolated from chlorophenol-contaminated soil, was shown to dechlorinate tetrachlorohydroquinone, the first intermediate in pentachlorophenol and 2,3,5,6-tetrachlorophenol degradation. Degradation of tetrachlorohydroquinone was catalyzed by a soluble enzyme(s). The reaction sequence for complete dechlorination involved hydroxylation and three reductive dechlorinations, producing 1,2,4-trihydroxybenzene. All chlorines were thus removed from the polychlorinated compound before ring cleavage.

Journal Article↗
PubMed1990

Bacterial degradation of ring-chlorinated acetophenones.

Two strains, Alcaligenes sp. strain ACA and Pseudomonas fluorescens ACB, isolated from acetophenone and 4'-hydroxyacetophenone enrichments, respectively, cometabolize a range of chlorinated acetophenones (CAs). A biological Baeyer-Villiger reaction converts the CA to chlorophenyl acetate. This is evident only in the presence of an esterase inhibitor, since the CA is normally rapidly hydrolyzed to a chlorophenol which has the same substitution pattern as the original ketone. The oxygenase that attacks the ketone uses NADPH in the incorporation of one atom of O(2) and is strongly inhibited by phenols that bear an ortho or meta chlorine or bromine, but much less by cresols or phenol itself. A feedback phenomenon may thus account for the inability of strain ACA to grow on CAs, which also fail to induce the cells for their own metabolism.

Journal Article↗
PubMed1991

Effects of sulfuroxy anions on degradation of pentachlorophenol by a methanogenic enrichment culture.

We studied the degradation of pentachlorophenol (PCP) under methanogenic and sulfate-reducing conditions with an anaerobic mixed culture derived from sewage sludge. The consortium degraded PCP via 2,3,4,5-tetrachlorophenol, 3,4,5-trichlorophenol, and 3,5-dichlorophenol and eventually accumulated 3-chlorophenol. Dechlorination of PCP and metabolites was inhibited in the presence of sulfate, thiosulfate, and sulfite. A decrease in the rate of PCP transformation was noted when the endogenous dissolved H(2) was depleted below 0.11 muM in sulfate-reducing cultures. The effect on dechlorination observed with sulfate could be relieved by addition of molybdate, a competitive inhibitor of sulfate reduction. Addition of H(2) reduced the inhibition observed with sulfuroxy anions. The inhibitory effect of sulfuroxy anions may be due to a competition for H(2) between sulfate reduction and dechlorination. When cultured under methanogenic conditions, the consortium degraded several chlorinated and brominated phenols.

Journal Article↗
PubMed1992

Preparation of encapsulated microbial cells for environmental applications.

An improved method for the encapsulation of bacteria into microspheres of alginate, agarose, or polyurethane is described. Cell suspensions were passed through a low-pressure nozzle into an aqueous phase where matrix polymerization or gelation yielded beads 2 to 50 mum in diameter. Trials with a chlorophenol-degrading Flavobacterium species showed that cells entrapped by these procedures were as catabolically active as free cells. These types of beads should have numerous applications in the fields of environmental science and engineering.

Journal Article↗
PubMed1992

Role of sulfate concentration in dechlorination of 3,4,5-trichlorocatechol by stable enrichment cultures grown with coumarin and flavanone glycones and aglycones.

Metabolically stable anaerobic enrichment cultures have been obtained from sediment samples contaminated with chlorophenolic compounds. Enrichment was carried out with esculin, esculetin, naringin, naringenin, fraxin, quercetin, and acetate in media with two sulfate concentrations. These cultures were used to examine the O-demethylation of 4,5,6-trichloroguaiacol and the dechlorination of 3,4,5-trichlorocatechol. Whereas O-demethylation was observed in all cultures, the occurrence of dechlorination was significantly more restricted. The presence of the carbohydrate moiety in the cultures enriched with the glycones repressed development of populations which were able to carry out dechlorination. Although sulfate at a concentration of 2 g/liter in the primary enrichments blocked the development of populations able to bring about dechlorination, addition of sulfate at this concentration did not inhibit dechlorination in cultures possessing this capability. Different dichlorocatechol isomers were produced under the various conditions, so that in view of the established resistance of some of these to further dechlorination, the ultimate fate of 3,4,5-trichlorocatechol in the natural environment remains partly unresolved. No enrichment culture containing a low sulfate concentration was able to dechlorinate either 2,4,5-trichlorophenol or 2,4,6-trichlorobenzoate.

Anaerobiosis↗
PubMed1992

Conversion of cis unsaturated fatty acids to trans, a possible mechanism for the protection of phenol-degrading Pseudomonas putida P8 from substrate toxicity.

A trans unsaturated fatty acid was found as a major constituent in the lipids of Pseudomonas putida P8. The fatty acid was identified as 9-trans-hexadecenoic acid by gas chromatography, argentation thin-layer chromatography, and infrared absorption spectrometry. Growing cells of P. putida P8 reacted to the presence of sublethal concentrations of phenol in the medium with changes in the fatty acid composition of the lipids, thereby increasing the degree of saturation. At phenol concentrations which completely inhibited the growth of P. putida, the cells were still able to increase the content of the trans unsaturated fatty acid and simultaneously to decrease the proportion of the corresponding 9-cis-hexadecenoic acid. This conversion of fatty acids was also induced by 4-chlorophenol in nongrowing cells in which the de novo synthesis of lipids had stopped, as shown by incorporation experiments with labeled acetate. The isomerization of the double bond in the presence of chloramphenicol indicates a constitutively operating enzyme system. The cis-to-trans modification of the fatty acids studied here apparently is a new way of adapting the membrane fluidity to the presence of phenols, thereby compensating for the elevation of membrane permeability induced by these toxic substances.

Adaptation, Physiological↗
PubMed1995

Toxicity of N-substituted aromatics to acetoclastic methanogenic activity in granular sludge.

N-substituted aromatics are important priority pollutants entering the environment primarily through anthropogenic activities associated with the industrial production of dyes, explosives, pesticides, and pharmaceuticals. Anaerobic treatment of wastewaters discharged by these industries could potentially be problematical as a result of the high toxicity of N-substituted aromatics. The objective of this study was to examine the structure-toxicity relationships of N-substituted aromatic compounds to acetoclastic methanogenic bacteria. The toxicity was assayed in serum flasks by measuring methane production in granular sludge. Unacclimated cultures were used to minimize the biotransformation of the toxic organic chemicals during the test. The nature and the degree of the aromatic substitution were observed to have a profound effect on the toxicity of the test compound. Nitroaromatic compounds were, on the average, over 500-fold more toxic than their corresponding aromatic amines. Considering the facile reduction of nitro groups by anaerobic microorganisms, a dramatic detoxification of nitroaromatics towards methanogens can be expected to occur during anaerobic wastewater treatment. While the toxicity exerted by the N-substituted aromatic compounds was closely correlated with compound apolarity (log P), it was observed that at any given log P, N-substituted phenols had a toxicity that was 2 orders of magnitude higher than that of chlorophenols and alkylphenols. This indicates that toxicity due to the chemical reactivity of nitroaromatics is much more important than partitioning effects in bacterial membranes.

Biotransformation↗
PubMed1996

Initial Characterization of a Reductive Dehalogenase from Desulfitobacterium chlororespirans Co23.

Desulfitobacterium chlororespirans Co23 is capable of using 3-chloro-4-hydroxybenzoate as terminal electron acceptor for growth. Membrane preparations from cells grown fermentatively on pyruvate in the presence of 3-chloro-4-hydroxybenzoate dechlorinated this compound at a rate of 3.9 nmol min(sup-1) mg of protein(sup-1). Fivefold-greater dechlorination rates were measured with reduced methyl viologen as the artificial electron donor. Reduced benzyl viologen, NADH, NADPH, reduced flavin adenine dinucleotide, and reduced flavin mononucleotide could not substitute for reduced methyl viologen. The maximal initial rate of catalysis was achieved at pH 6.5 and 60(deg)C. The membrane-bound dechlorinating enzyme system was not oxygen sensitive and was stable at 57(deg)C for at least 2 h. Sulfite inhibited dechlorination in cell-free assays, whereas sulfate did not. Several chlorophenols were dehalogenated exclusively in the ortho position by cell extracts.

Journal Article↗
PubMed1997

Monitoring of an Alkaline 2,4,6-Trichlorophenol-Degrading Enrichment Culture by DNA Fingerprinting Methods and Isolation of the Responsible Organism, Haloalkaliphilic Nocardioides sp. Strain M6.

A site situated near Alkali Lake (Oregon) and highly contaminated by chloroaromatic compounds was chosen for isolation of alkaliphilic chlorophenol-degrading bacteria. Prolonged cultivation of an enrichment culture followed by successive transfers resulted in a strong increase in the 2,4,6-trichlorophenol (2,4,6-TCP) degradation rate. Repetitive extragenic palindromic PCR and amplified ribosomal DNA restriction analysis were applied to distinguish members of the enrichment culture and monitor them during the enrichment procedure. Comparison of the fingerprints of the isolates obtained from the enrichment culture and its total DNA fingerprint indicated the presence of an unidentified bacterium in the enrichment culture, assisting in its isolation. The 2,4,6-TCP-degrading isolate, M6, was tentatively identified as a Nocardioides sp. strain based on its partial 16S RNA sequence and fatty acid profile. Strain M6 was capable of utilizing up to 1.6 g of 2,4,6-TCP per liter as a sole carbon and energy source and could also grow on 2,4-dichlorophenol and 2,4,5-trichlorophenol. A high-cell-density suspension of this strain degraded a wide range of chlorinated phenols from di- to pentachlorophenol while showing a clear preference for phenols containing chlorine substituents in positions 2 plus 4. Based on its optimal pH (9.0 to 9.4) and sodium ion concentration (0.2 to 0.4 M) for growth, Nocardioides sp. strain M6 is a slightly halophilic alkaliphile.

Journal Article↗
PubMed2000

Generation of novel bacterial regulatory proteins that detect priority pollutant phenols.

The genetic systems of bacteria that have the ability to use organic pollutants as carbon and energy sources can be adapted to create bacterial biosensors for the detection of industrial pollution. The creation of bacterial biosensors is hampered by a lack of information about the genetic systems that control production of bacterial enzymes that metabolize pollutants. We have attempted to overcome this problem through modification of DmpR, a regulatory protein for the phenol degradation pathway of Pseudomonas sp. strain CF600. The phenol detection capacity of DmpR was altered by using mutagenic PCR targeted to the DmpR sensor domain. DmpR mutants were identified that both increased sensitivity to the phenolic effectors of wild-type DmpR and increased the range of molecules detected. The phenol detection characteristics of seven DmpR mutants were demonstrated through their ability to activate transcription of a lacZ reporter gene. Effectors of the DmpR derivatives included phenol, 2-chlorophenol, 2,4-dichlorophenol, 4-chloro-3-methylphenol, 2,4-dimethylphenol, 2-nitrophenol, and 4-nitrophenol.

Bacterial Proteins↗
PubMed2001

Energy yield of respiration on chloroaromatic compounds in Desulfitobacterium dehalogenans.

The amount of energy that can be conserved via halorespiration by Desulfitobacterium dehalogenans JW/IU-DC1 was determined by comparison of the growth yields of cells grown with 3-chloro-4-hydroxyphenyl acetate (Cl-OHPA) and different electron donors. Cultures that were grown with lactate, pyruvate, formate, or hydrogen as an electron donor and Cl-OHPA as an electron acceptor yielded 3.1, 6.6, 1.6, and 1.6 g (dry weight) per mol of reduction equivalents, respectively. Fermentative growth on pyruvate yielded 14 g (dry weight) per mol of pyruvate oxidized. Pyruvate was not fermented stoichiometrically to acetate and lactate, but an excess of acetate was produced. Experiments with 13C-labeled bicarbonate showed that during pyruvate fermentation, approximately 9% of the acetate was formed from the reduction of CO2. Comparison of the growth yields suggests that 1 mol of ATP is produced per mol of acetate produced by substrate-level phosphorylation and that there is no contribution of electron transport phosphorylation when D. dehalogenans grows on lactate plus Cl-OHPA or pyruvate plus Cl-OHPA. Furthermore, the growth yields indicate that approximately 1/3 mol of ATP is conserved per mol of Cl-OHPA reduced in cultures grown in formate plus Cl-OHPA and hydrogen plus Cl-OHPA. Because neither formate nor hydrogen nor Cl-OHPA supports substrate-level phosphorylation, energy must be conserved through the establishment of a proton motive force. Pyruvate ferredoxin oxidoreductase, lactate dehydrogenase, formate dehydrogenase, and hydrogenase were localized by in vitro assays with membrane-impermeable electron acceptors and donors. The orientation of chlorophenol-reductive dehalogenase in the cytoplasmic membrane, however, could not be determined. A model is proposed, which may explain the topology analyses as well as the results obtained in the yield study.

Bacteria, Anaerobic↗
PubMed2003

Conversion of 2-fluoromuconate to cis-dienelactone by purified enzymes of Rhodococcus opacus 1cp.

The present study describes the (19)F nuclear magnetic resonance analysis of the conversion of 3-halocatechols to lactones by purified chlorocatechol 1,2-dioxygenase (ClcA2), chloromuconate cycloisomerase (ClcB2), and chloromuconolactone dehalogenase (ClcF) from Rhodococcus opacus 1cp grown on 2-chlorophenol. The 3-halocatechol substrates were produced from the corresponding 2-halophenols by either phenol hydroxylase from Trichosporon cutaneum or 2-hydroxybiphenyl 3-mono-oxygenase from Pseudomonas azelaica. Several fluoromuconates resulting from intradiol ring cleavage by ClcA2 were identified. ClcB2 converted 2-fluoromuconate to 5-fluoromuconolactone and 2-chloro-4-fluoromuconate to 2-chloro-4-fluoromuconolactone. Especially the cycloisomerization of 2-fluoromuconate is a new observation. ClcF catalyzed the dehalogenation of 5-fluoromuconolactone to cis-dienelactone. The ClcB2 and ClcF-mediated reactions are in line with the recent finding of a second cluster of chlorocatechol catabolic genes in R. opacus 1cp which provides a new route for the microbial dehalogenation of 3-chlorocatechol.

Adipates↗
PubMed2004

Root nodule Bradyrhizobium spp. harbor tfdAalpha and cadA, homologous with genes encoding 2,4-dichlorophenoxyacetic acid-degrading proteins.

The distribution of tfdAalpha and cadA, genes encoding 2,4-dichlorophenoxyacetate (2,4-D)-degrading proteins which are characteristic of the 2,4-D-degrading Bradyrhizobium sp. isolated from pristine environments, was examined by PCR and Southern hybridization in several Bradyrhizobium strains including type strains of Bradyrhizobium japonicum USDA110 and Bradyrhizobium elkanii USDA94, in phylogenetically closely related Agromonas oligotrophica and Rhodopseudomonas palustris, and in 2,4-D-degrading Sphingomonas strains. All strains showed positive signals for tfdAalpha, and its phylogenetic tree was congruent with that of 16S rRNA genes in alpha-Proteobacteria, indicating evolution of tfdAalpha without horizontal gene transfer. The nucleotide sequence identities between tfdAalpha and canonical tfdA in beta- and gamma-Proteobacteria were 46 to 57%, and the deduced amino acid sequence of TfdAalpha revealed conserved residues characteristic of the active site of alpha-ketoglutarate-dependent dioxygenases. On the other hand, cadA showed limited distribution in 2,4-D-degrading Bradyrhizobium sp. and Sphingomonas sp. and some strains of non-2,4-D-degrading B. elkanii. The cadA genes were phylogenetically separated between 2,4-D-degrading and nondegrading strains, and the cadA genes of 2,4-D degrading strains were further separated between Bradyrhizobium sp. and Sphingomonas sp., indicating the incongruency of cadA with 16S rRNA genes. The nucleotide sequence identities between cadA and tftA of 2,4,5-trichlorophenoxyacetate-degrading Burkholderia cepacia AC1100 were 46 to 53%. Although all root nodule Bradyrhizobium strains were unable to degrade 2,4-D, three strains carrying cadA homologs degraded 4-chlorophenoxyacetate with the accumulation of 4-chlorophenol as an intermediate, suggesting the involvement of cadA homologs in the cleavage of the aryl ether linkage. Based on codon usage patterns and GC content, it was suggested that the cadA genes of 2,4-D-degrading and nondegrading Bradyrhizobium spp. have different origins and that the genes would be obtained in the former through horizontal gene transfer.

2,4-Dichlorophenoxyacetic Acid↗