Biodegradation kinetics of 2,4,6-Trichlorophenol by an acclimated mixed microbial culture under aerobic conditions

The objective of this study was to achieve a better quantitative understanding of the kinetics of 2,4,6-trichlorophenol (TCP) biodegradation by an acclimated mixed microbial culture. An aerobic mixed microbial culture, obtained from the aeration basin of the wastewater treatment plant, was acclimated in shake flasks utilizing various combinations of 2,4,6-TCP (25–100 mg l⁻¹), phenol (300 mg l⁻¹) and glycerol (2.5 mg l⁻¹) as substrates. Complete primary TCP degradation and a corresponding stoichiometric release of chloride ion were observed by HPLC and IEC analytical techniques, respectively. The acclimated cultures were then used as an inoculum for bench scale experiments in a 4 l stirred-tank reactor (STR) with 2,4,6-TCP as the sole carbon/energy (C/E) source. The phenol acclimated mixed microbial culture consisted of primarily Gram positive and negative rods and was capable of degrading 2,4,6-TCP completely. None of the predicted intermediate compounds were detected by gas chromatography in the cell cytoplasm or supernatant. Based on the disappearance of 2,4,6-TCP, degradation was well modelled by zero-order kinetics which was also consistent with the observed oxygen consumption. Biodegradation rates were compared for four operating conditions including two different initial 2,4,6-TCP concentrations and two different initial biomass concentrations. While the specific rate constant was not dependent on the initial 2,4,6-TCP concentration, it did depend on the initial biomass concentration (X _init). A lower biomass concentration gave a much higher zero-order specific degradation rate. This behaviour was attributed to a lower average biomass age or cell retention time (θ_x) for these cultures. The implications of this investigation are important for determining and predicting the potential risks associated with TCP, its degradation in the natural environment or the engineering implications for ex situ treatment of contaminated ground water or soil.     

Environmental significance of O-demethylation of chloroanisoles by soil bacterial isolates as a mechanism that improves the overall biodegradation of chlorophenols

The biodegradation rate of chlorophenols in the environment seems to be limited by a competitive mechanism of O-methylation which produces chloroanisoles with a high potential of being bioconcentrated in living organisms. In this work we report for the first time the isolation of three soil bacterial strains able to efficiently degrade 2,4,6-trichloroanisole (2,4,6-TCA). These strains were identified as Xanthomonas retroflexus INBB4, Pseudomonas putida INBP1 and Acinetobacter radioresistens INBS1. In these isolates 2,4,6-TCA was efficiently metabolized in a minimal medium containing methanol and 2,4,6-TCA as the only carbon sources, with a concomitant release of 3 mol of chloride ion from 1 mol of 2,4,6-TCA, indicating complete dehalogenation of 2,4,6-TCA. 2,4,6-trichlorophenol (2,4,6-TCP) was identified as a degradative intermediate, indicating that 2,4,6-TCA underwent O-demethylation as the first step in the biodegradation process. 2,4,6-TCP was further transformed into 2,6-dichloro-para-hydroquinone (2,6-DCHQ) and subsequently mineralized. The degradation of chloroanisoles could improve the overall biodegradation of chlorophenols in the environment, because those chlorophenols previously biomethylated might also be later biodegraded. Xanthomonas retroflexus INBB4 has two O-demethylation systems: one is an oxygenase-type demethylase, and the other is a tetrahydrofolate (THF)-dependent O-demethylase. On the contrary O-demethylation of 2,4,6-TCA in P. putida INBP1 is just catalysed by an oxygenase-type NADH/NADPH-dependent O-demethylase, whereas in A. radioresistens INBS1 a THF-dependent O-demethylase activity was detected.     

Isolation of Pseudomonas pickettii strains that degrade 2,4,6-trichlorophenol and their dechlorination of chlorophenols.

Three strains of Pseudomonas pickettii that can grow with 2,4,6-trichlorophenol (2,4,6-TCP) as the sole source of carbon and energy were isolated from different mixed cultures of soil bacterial populations that had been acclimatized to 2,4,6-TCP. These strains released 3 mol of chloride ion from 1 mol of 2,4,6-TCP during the complete degradation of the TCP. Of these strains, P. pickettii DTP0602 in high-cell-density suspension cultures dechlorinated various chlorophenols (CPs). Cells that were preincubated with 2,4,6-TCP converted isomers of 4-CP to the corresponding chloro-p-hydroquinones, but those preincubated with 4-CP converted CPs lacking a chlorine atom(s) at the o position to isomers of chlorocatechol. The ability of DTP0602 to dechlorinate 2,4,6-TCP was induced by 2,6-dichlorophenol, 2,3,6- and 2,4,6-TCP, and 2,3,4,6-tetrachlorophenol and was repressed in the presence of succinate or glucose.     

Isolation of Pseudomonas pickettii strains that degrade 2,4,6-trichlorophenol and their dechlorination of chlorophenols.

Three strains of Pseudomonas pickettii that can grow with 2,4,6-trichlorophenol (2,4,6-TCP) as the sole source of carbon and energy were isolated from different mixed cultures of soil bacterial populations that had been acclimatized to 2,4,6-TCP. These strains released 3 mol of chloride ion from 1 mol of 2,4,6-TCP during the complete degradation of the TCP. Of these strains, P. pickettii DTP0602 in high-cell-density suspension cultures dechlorinated various chlorophenols (CPs). Cells that were preincubated with 2,4,6-TCP converted isomers of 4-CP to the corresponding chloro-p-hydroquinones, but those preincubated with 4-CP converted CPs lacking a chlorine atom(s) at the o position to isomers of chlorocatechol. The ability of DTP0602 to dechlorinate 2,4,6-TCP was induced by 2,6-dichlorophenol, 2,3,6- and 2,4,6-TCP, and 2,3,4,6-tetrachlorophenol and was repressed in the presence of succinate or glucose.     

Utilization of d-carnitine by Pseudomonas sp. AK 1

Abstract The degradation of chlorophenols by Alcaligenes eutrophus JMP134 (pJP4) was studied. The strain grew on 2,4,6-trichlorophenol or 2,4,6-tribromophenol as the sole carbon and energy source. Complete degradation of 2,4,6-trichlorophenol was confirmed by chloride release and gas chromatography analysis of supernatants from growth cultures. The 2,3,5-, 2,3,4-, 2,3,6-and 2,4,5-isomers of trichlorophenol did not support growth. However, up to 40% of 2,4,5-trichlorophenol was mineralized during growth of A. eutrophus on chemostats fed with either phenol (0.4 mM) or 2,4,6-trichlorophenol (0.4 mM) plus 2,4,5-trichlorophenol (0.1 mM). Growth on 2,4,6-trihalophenols was also observed in A. Eutrophus JMP222, the strain lacking pJP4, suggesting that this new degradative ability reported for A. eutrophus is not related to pJP4 encoded catabolic functions.     

Isolation and characterization of a novel Dehalobacter species strain TCP1 that reductively dechlorinates 2,4,6-trichlorophenol

Chlorophenols are widely used as biocides, leading them to being prevalent environmental contaminants that pose toxic threats to ecosystems. In this study, a Dehalobacter species strain TCP1 was isolated from a digester sludge sample, which is able to dechlorinate 2,4,6-trichlorophenol (2,4,6-TCP) to 4-monochlorophenol (4-MCP) with H₂ as the sole electron donor and acetate as the carbon source. Strain TCP1 also distinguishes itself from other Dehalobacter species with its capability to dechlorinate tetrachloroethene or trichloroethene (TCE) to both cis- and trans-dichloroethenes in a ratio of 5.6 (±0.2):1. The growth yields of strain TCP1 on TCE and 2,4,6-TCP were 4.14 × 10¹³ and 5.77 × 10¹³ cells mol^?1 of Cl^? released, respectively. Strain TCP1 contains five unusually long 16S rRNA gene copies per genome, and the extra length is due to the ~110 bp insertion sequences at their 5′-ends. This suggests that strain TCP1 may represent a novel Dehalobacter species. A putative chlorophenol reductive dehalogenase gene—debcprA—was identified to catalyze the ortho-chlorine removal from 2,4,6-TCP. Both the culture-dependent and housekeeping rpoB gene-based approaches indicate the purity of the culture. Strain TCP1 can serve as a promising candidate for the bioremediation of 2,4,6-TCP contaminated sites, and its discovery expands our understanding of metabolic capabilities of Dehalobacter species.     

Biodegradation of 2,4,6-TCA by the white-rot fungus Phlebia radiata is initiated by a phase I (O-demethylation)-phase II (O-conjugation) reactions system: implications for the chlorine cycle

Thirteen species of white-rot fungi tested have been shown to efficiently biodegrade 1 mM 2,4,6-trichloroanisole (2,4,6-TCA) in liquid cultures. The maximum biodegradation rate (94.5% in 10-day incubations) was exhibited by a Phlebia radiata strain. The enzymes of the ligninolytic complex, laccase, lignin peroxidase (LiP), manganese peroxidase (MnP) and versatile peroxidase (VP) were not able to transform 2,4,6-TCA in in vitro reactions, indicating that the ligninolytic complex was not involved in the initial attack to 2,4,6-TCA. Instead, the first biodegradative steps were carried out by a phase I and phase II reactions system. Phase I reaction consisted on a O-demethylation catalysed by a microsomal cytochrome P-450 monooxygenase to produce 2,4,6-trichlorophenol (2,4,6-TCP). Later, in a phase II reaction catalysed by a microsomal UDP-glucosyltransferase, 2,4,6-TCP was detoxified by O-conjugation with d -glucose to produce 2,4,6-TCP-1- O- d -glucoside (TCPG). This compound accumulated in culture supernatants, reaching its maximum concentration between 48 and 72 h of growth. TCPG levels decreased constantly by the end of fermentation, indicating that it was subsequently metabolized. A catalase activity was able to break in vitro the glycosidic link to produce 2,4,6-TCP, whereas ligninolytic enzymes did not have a significant effect on the biotransformation of that compound. Once formed, 2,4,6-TCP was further degraded as detected by a concomitant release of 2.6 mol of chloride ions by 1 mol of initial 2,4,6-TCA, indicating that this compound underwent almost a complete dehalogenation and biodegradation. It was concluded that P. radiata combines two different degradative mechanisms in order to biodegrade 2,4,6-TCA. The significance of the capability of white-rot fungi to O-demethylate chloroanisoles for the global chlorine cycle is discussed.     

A Previously Unexposed Forest Soil Microbial Community Degrades High Levels of the Pollutant 2,4,6-Trichlorophenol

2,4,6-Trichlorophenol (2,4,6-TCP) is a hazardous pollutant that is efficiently degraded by some aerobic soil bacterial isolates under laboratory conditions. The degradation of this pollutant in soils and its effect on the soil microbial community are poorly understood. We report here the ability of a previously unexposed forest soil microbiota to degrade high levels of 2,4,6-TCP and describe the changes in the soil microbial community found by terminal restriction fragment length polymorphism (T-RFLP) analysis. After 30 days of incubation, about 50% degradation of this pollutant was observed in soils amended with 50 to 5,000 ppm of 2,4,6-TCP. The T-RFLP analysis showed that the soil bacterial community was essentially unchanged after exposure to up to 500 ppm of 2,4,6-TCP. However, a significant decrease in richness was found with 2,000 and 5,000 ppm of 2,4,6-TCP, even though the removal of this pollutant remained high. The introduction of Ralstonia eutropha JMP134 or R. eutropha MS1, two efficient 2,4,6-TCP degraders, to this soil did not improve degradation of this pollutant, supporting the significant bioremediation potential of this previously unexposed, endogenous forest soil microbial community.     

Degradation of 2,4,6-TCP and a mixture of isomeric chlorophenols by immobilized Streptomyces rochei 303

We investigated the degradation of 2,4,6-trichlorophenol (2,4,6-TCP) by cells of Streptomyces rochei 303 immobilized on various carriers. Polycaproamide fibre was chosen as the optimal carrier for immobilization. The cells immobilized on this carrier degraded high-concentrations of individual chlorophenols and their mixtures: from mono- to pentachlorophenol including the most persistent meta-substituted derivatives. During continuous fermentation in a column with continuous substrate and air flow at a maximal degraded concentration of 2,4,6-TCP of 1 g/l and the specific flow rate of 0.08 h^–1, the efficiency of degradation was 720 mg 2,4,6-TCP/day (36 mg 2,4,6-TCP/day per gram of carrier). The above system of immobilized cells was operated continuously without any loss of activity for 2.5 months, the amount of degraded 2,4,6-TCP being 54 g. At a lower concentration of the reagent (150 mg/l) the system was operated without any decrease in its degradability and without any additional carbon source for 11 months. Correspondence to: L. A. Golovleva     

厌氧微生物菌群XH-1对2,4,6-三氯苯酚的降解特性

有机污染物2,4,6-三氯苯酚(2,4,6-TCP)普遍存在于地下水和河流底泥等厌氧环境中。为了探究厌氧微生物菌群XH-1对2,4,6-TCP的降解能力,本研究以2,4,6-TCP为底物,接种XH-1建立微宇宙培养体系,并以中间产物4-氯苯酚(4-CP)和苯酚为底物分别进行分段富集培养,利用高效液相色谱分析底物的降解转化,同时基于16S rRNA基因高通量测序分析微生物群落结构变化。结果表明: 2,4,6-TCP(122 μmol·L^-1)以0.15 μmol·d^-1的速率在80 d内被完全降解转化,降解中间产物分别为2,4-二氯苯酚(2,4-DCP)、4-氯苯酚和苯酚,所有中间产物最终在325 d被完全降解。高通量测序结果表明,脱卤杆菌和脱卤球菌可能驱动2,4,6-TCP还原脱氯,其中,脱卤球菌可能在4-CP的脱氯转化中发挥重要作用,并与丁酸互营菌和产甲烷菌联合作用彻底降解2,4,6-TCP。     

Effects of glucose and phenylalanine upon 2,4,6-trichlorophenol degradation by Pseudomonas paucimobilis S37 cells in a no-growth state

Pseudomonas paucimobilis S37, a strain able to degrade 2,4,6-trichlorophenol (246-TCP), was isolated from an aquatic environment polluted with this compound. The effect of two natural organic compounds on the degradation of 246-TCP by this strain, in a no-growth state, was studied. Bacterial cultures were exposed to 0.1 mM and 0.5 mM of 246-TCP, alone, or in the presence of similar concentrations of glucose, a growth supporting substrate, or phenylalanine, a no-growth supporting compound. The effects on viable counts and 246-TCP degradation were measured. The bacterial culture died with 0.5 mM 246-TCP. This effect was overcome by the presence of glucose or phenylalanine, although no degradation of 246-TCP was detected. At 0.1 mM 246-TCP, the viability was not altered, and cells were able to degrade this compound. Glucose at 0.1 mM increased the degradative activity, but higher levels were inhibitory. Phenylalanine at 0.67 mM or higher concentration was also inhibitory of the 246-TCP degradation.     

Bioremediation 2,4,6,-Trichlorophenol (2,4,6-TCP) by Shigella sp. S2 Isolated from Industrial Dumpsite

A bacterium that utilizes 2,4,6-trichlorophenol (2,4,6-TCP) as a sole source of carbon and energy was isolated from an industrial dumpsite, the bacterium designated as strain S2. Degradation was routinely monitored by observing growth analysis, chloride release assay, and ring cleavage activity and was further confirmed by gas chromatography (GC) analysis. The bacterium was found to degrade up to 90% of 2,4,6-TCP at 1.5 mM concentration. The bacteria were characterized morphologically, biochemically, and by 16S rRNA gene sequencing, which showed 99% sequence similarity with Shigella sp. This is the first report that Shigella sp. was able to degrade 2,4,6-TCP. This strain was found to be novel and a potential 2,4,6-TCP degrader. Further, this strain may be used for bioremediation of 2,4,6-TCP–containing waste in the environment.     

Chlorophenol removal from soil suspensions: Effects of a specialised microbial inoculum and a degradable analogue

Two soils of different contamination history were tested in slurry for their self-remediability towards mono-, di- and trisubstituted chlorophenols. The landfill soil showed poor ability in removing the compounds. Instead, the soil from the golf course, treated for many years with a 2,4,6-trichlorophenol derivative (Prochloraz), remediated different concentrations of the same 2,4,6TCP, 2,4-dichlorophenol and monochlorophenol isomers, singly and in mixtures, at varying degradation rates. Ralstonia eutropha TCP, a specialised microorganism capable of degrading 2,4,6TCP, proved highly efficient in removing the compound from both tested soils. The same microbial inoculum allowed total removal of the ternary mixture of monochlorophenol isomers from the golf course soil, but it did not accelerate the removal of the same compounds when singly supplied. The addition of phenol as a degradable analogue was more effective in co-metabolically removing not only the single monochlorophenols, but also their mixtures, the removal occurring faster and independently of the presence of the microbial inoculum. From the golf course soil, a microorganism, phenotypically and genetically identical to R. eutropha TCP, was isolated and classified as R. eutropha TCP II.     

Poly-beta-hydroxyalkanoates consumption during degradation of 2,4,6-trichlorophenol by Sphingopyxis chilensis S37

AIMS: To analyse the possible effect of poly-beta-hydroxyalkanoate (PHA) consumption on 2,4,6-trichlorophenol (2,4,6-TCP) degradation during starvation by Sphingopyxis chilensis S37 strain, which stores PHAs and degrades 2,4,6-TCP. METHODS AND RESULTS: The strain was inoculated in saline solution supplemented with 2,4,6-TCP (25-400 microm). Chlorophenol degradation was followed both spectrophotometrically and by chlorine released; viable bacterial counts were also determined. Cells starved for 24, 48 or 72 h were incubated with 25 microm of 2,4,6-TCP and PHA in cells investigated by spectrofluorimetric and flow cytometry. Results demonstrated that starvation decreased the ability to degrade 2,4,6-TCP. After 72 h of starvation, degradation of 2,4,6-TCP decreased to less than 10% and the relative PHA content diminished to ca 50% during the first 24 h. CONCLUSION: Utilization of PHA may be an important factor for the degradation of toxic compounds, such as 2,4,6-TCP, in bacterial strains unable to use this toxic compound as carbon and energy source. SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first study describing a relationship between intracellular PHA consumption and 2,4,6-TCP degradation. Therefore, PHAs provides an endogenous carbon and energy source under starvation and can play a significant role in the degradation of toxic compounds.     

Aerobic degradation of 2,4-dichlorophenoxyacetic acid and other chlorophenols by <Emphasis Type="Italic">Pseudomonas</Emphasis> strains indigenous to contaminated soil in South Africa: Growth kinetics and degradation pathway

Three indigenous pseudomonads, Pseudomonas putida DLL-E4, Pseudomonas reactans and Pseudomonas fluorescens, were isolated from chlorophenol-contaminated soil samples collected from a sawmill located in Durban (South Africa). The obtained isolates were tested for their ability to degrade chlorophenolic compounds: 2,4-dichlorophenoxyacetic acid (2,4-D), 2,4-dichlorophenol (2,4-DCP) and 2,4,6-trichlorophenol (2,4,6-TCP) in batch cultures. The isolates were found to effectively degrade up to 99.5, 98.4 and 94.0% with a degradation rate in the range of 0.67–0.99 (2,4-D), 0.57–0.93 (2,4-DCP) and 0.30–0.39 (2,4,6-TCP) mgL^–1 day^–1 for 2,4-D; 2,4-DCP and 2,4,6-TCP, respectively. The degradation kinetics model revealed that these organisms could tolerate up to 600 mg/L of 2,4-DCP. Catechol 2,3-dioxygenase activity detected in the crude cell lysates of P. putida DLL-E4 and P. reactans was 21.9- and 37.6-fold higher than catechol 1,2-dioxygenase activity assayed, suggesting a meta-pathway for chlorophenol degradation by these organisms. This is also supported by the generally high expression of C23O gene (involved in meta-pathway) relative to tfdC gene (involved in ortho-pathway) expression. Results of this study will be helpful in the exploitation of these organisms and/or their enzymes in bioremediation strategies for chlorophenol-polluted environment.     

Transformation of 2,4,6-trichlorophenol by the white rot fungi Panus tigrinus and Coriolus versicolor

The toxicity of thirteen isomers of mono-, di-, tri- and pentachlorophenols was tested in potato-dextrose agar cultures of the white rot fungi Panus tigrinus and Coriolus versicolor. 2,4,6-Trichlorophenol (2,4,6-TCP) was chosen for further study of its toxicity and transformation in liquid cultures of these fungi. Two schemes of 2,4,6-TCP addition were tested to minimize its toxic effect to fungal cultures: stepwise addition from the moment of inoculation and single addition after five days of growth. In both cases the ligninolytic enzyme systems of both fungi were found to be responsible for 2,4,6-TCP transformation. 2,6-Dichloro-1,4-hydroquinol and 2,6-dichloro-1,4-benzoquinone were found as products of primary oxidation of 2,4,6-TCP by intact fungal cultures and purified ligninolytic enzymes, Mn-peroxidases and laccases of both fungi. However, primary attack of 2,4,6-TCP in P. tigrinus culture was conducted mainly by Mn-peroxidase, while in C. versicolor it was catalyzed predominantly by laccase, suggesting a different mode of regulation of these enzymes in the two fungi.     

Role of mycelium and extracellular protein in the biodegradation of 2,4,6-trichlorophenol by Phanerochaete chrysosporium.

The biodegradation of 2,4,6-trichlorophenol (2,4,6-TCP) by Phanerochaete chrysosporium was studied in batch systems. In experiments with mycelial suspension, the degradation of 2,4,6-TCP was found to occur in the absence of ligninase. Chloride ion was recovered in nearly stoichiometric amounts at the end of the process. The microorganism did not retain its degradation ability for more than 6 days under substrate-deficient conditions. Neither the mycelium nor the extracellular protein alone could degrade 2,4,6-TCP; both were required for complete degradation to occur. In experiments in which 2,4,6-TCP was exposed to the culture supernatant separated from its mycelium, negligible degradation was obtained and no chloride ion was recovered. No degradation was observed even when the supernatant was supplemented with hydrogen peroxide as a possible cosubstrate. In experiments performed with washed mycelium separated from its supernatant, no degradation took place until the mycelium released additional extracellular protein 5 to 6 h into the incubation. Additions of washed mycelium separated from its supernatant to active cultures also produced an increase in the rate of degradation in correspondence with the protein release. The protein release was independent of the presence of 2,4,6-TCP. The addition of cycloheximide to inhibit the synthesis of de novo proteins completely suppressed the release of protein by the mycelium and resulted in no 2,4,6-TCP degradation. Additions of culture supernatants containing a high concentration of extracellular protein to active cultures produced an increase in the rate of 2,4,6-TCP degradation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Degradation of 2,4,6-trichlorophenol (2,4,6-TCP) by co-immobilization of anaerobic and aerobic microbial communities in an upflow reactor under air-limited conditions

The co-immobilization and the culture of anaerobic and aerobic communities was tested for the mineralization of 2,4,6-trichlorophenol (2,4,6-TCP). At first, the anaerobic microorganisms (aggregated into granules) were cultivated in an upflow anaerobic sludge blanket (UASB) reactor, in a continuous mode, with glucose, propionate, acetate (COD loading rate = 0.5-2.0 g COD/l per day, ratio 1:1:1) and 2,4,6-TCP (2,4,6-TCP loading rate = 25-278 micromol/l per day) as substrates. 2,4,6-TCP was degraded into 2,4-DCP and 4-CP, but it was not mineralized because of the low degradation rates of 4-CP. Furthermore, the highest loading rates of 2,4,6-TCP (>126 micromol/l per day) caused the inhibition of the strains degrading the propionate. The granules were therefore tested in association with the aerobic community. They were immobilized in kappa-carrageenan/gelatin [2% (w/w) of each polymer] gel beads and cultivated in a reactor, on their own (to test the influence of the gel), and then with the aerobic community, under anaerobic and air-limited conditions, respectively. The results showed that (1) the gel did not influence the activity of the granules, (2) the anaerobic and aerobic communities could be easily co-immobilized in gel beads and cultivated in a reactor, (3) the mineralization of 2,4,6-TCP (2,4,6-TCP loading rate = 10-506 micromol/l per day), its intermediates of degradation and the other substrates [glucose + acetate + propionate (ratio 1:1:1) = COD loading rate = 500 mg COD/l per day] could be obtained under air-limited conditions if the culture parameters were strictly controlled [airflow = 36-48 vvd (volume of air/volume of liquid in the reactor per day), pH value at around 7.5]. Finally, the gel did not retain its structure during the whole culture (263 days) in the air-limited reactor, but the anaerobic and aerobic communities retained their activities and worked together for the mineralization.     

Conversion of polychlorophenols by laccases with 1-hydroxybenzotriazole as a mediator

The action of purified laccase from the basidial fungi Cerrena unicolor and Trametes sp. on 2,4,6-trichlorophenol (2,4,6-TCP) and pentachlorophenol (PCP) was studied, including reactions involving 1-hydroxybenzotriazole as a mediator. Oxidation of 2,4,6-TCP by laccase without the mediator yielded 2,6-dichlorobenzoquinone as a primary conversion product, whereas PCP was not oxidized. Products of further conversion of 2,4,6-TCP and PCP formed with the presence of the mediator.     

Anaerobic transformation and toxicity of trichlorophenols in a stable enrichment culture.

The transformation and toxicity of trichlorophenols (TCPs) were studied with a methanogenic enrichment culture derived from sewage sludge. Transformation of TCPs rapidly resumed after heating of the culture at *) degrees C for 1 h, suggesting that the dechlorinating bacteria are spore-forming anaerobes. 2,4,6-TCP was rapidly dechlorinated via 2,4-dichlorophenol to 4-chlorophenol. During the transformation of 2,4,6-TCP, the most probable number of dechlorinating bacteria increased by 4 orders of magnitude. The most extensive dechlorination was observed in media with complex carbon sources such as yeast extract, peptone, and Casamino Acids, but glucose, galactose, and lactose were also used by the consortium. Experiments using chloramphenicol indicated that the reductive dechlorination of 2,4,6-TCP was regulated by an inducible enzyme system. The highest initial concentration at which dechlorination of 2,4,6-TCP was observed was 400 microM. 2,4,5-TCP and 3,4,5-TCP were dechlorinated to, respectively, 3,4-dichlorophenol and 3-chlorophenol at initial concentrations of less than or equal to 40 microM. Toxicity for the acid-producing and methanogenic bacteria in the consortium was a function of chemical structure, as the inhibition of these activities increased from 2,4,6-TCP, via 2,4,5-TCP, to 3,4,5,-TCP.