Biodegradation Of Pentachlorophenol Research Articles

Complete pentachlorophenol biodegradation in a dual-working electrode bioelectrochemical system: Performance and functional microorganism identification

Bioelectrochemical system (BES) can effectively promote the reductive dechlorination of chlorophenols (CPs). However, the complete degradation of CPs with sequential dechlorination and mineralization processes has rarely achieved from the BES. Here, a dual-working electrode BES was constructed and applied for the complete degradation of pentachlorophenol (PCP). Combined with DNA-stable isotope probing (DNA-SIP), the biofilms attached on the anodic and cathodic electrode in the BES were analyzed to explore the dechlorinating and mineralizing microorganisms. Results showed that PCP removal efficiency in the dual-working BES (84% for 21 days) was 4.1 and 4.7 times higher than those of conventional BESs with a single anodic or cathodic working electrode, respectively. Based on DNA-SIP and high-throughput sequencing analysis, the cathodic working electrode harbored the potential dechlorinators (Comamonas, Pseudomonas, Methylobacillus, and Dechlorosoma), and the anodic working enriched the potential intermediate mineralizing bacteria (Comamonas, Stenotrophomonas, and Geobacter), indicating that PCP could be completely degraded under the synergetic effect of these functional microorganisms. Besides, the potential autotrophic functional bacteria that might be involved in the PCP dechlorination were also identified by SIP labeled with 13C-NaHCO3. Our results proved that the dual-working BES could accelerate the complete degradation of PCP and enrich separately the functional microbial consortium for the PCP dechlorination and mineralization, which has broad potential for bioelectrochemical techniques in the treatment of wastewater contaminated with CPs or other halogenated organic compounds.

Optimizing rapid pentachlorophenol biodegradation using response surface methodology

Pentachlorophenol (PCP) is one of the most toxic pollutants in the environment during modern industrial processes. Statistical experimental designs based on biological methods optimized the PCP biodegradation by Bacillus mucilaginosus and Pseudomonas plecoglossicida. Four factors were selected for PCP removal; glucose, ferric ammonium citrate, PCP concentration, and incubation period. PBD and CCD were performed to recognize the maximum PCP biodegradation. The maximum PCP biodegradation in PBD by B. mucilaginosus was obtained at glucose, 0.5 (g/l); ferric ammonium citrate, 0.5 (g/l); PCP concentration, 300 (mg/l) and incubation period, 3 (days) while the maximum conditions by P. plecoglossicida were glucose, 0.5 (g/l); ferric ammonium citrate, 0.5 (g/l); PCP concentration, 100 (mg/l) and incubation period, 3 (days). In addition, CCD predicted the optimum predicted degradation of PCP (100%) by the two selected strains using glucose (1.0 g/l), ferric ammonium citrate (0.059 mg/l), PCP concentration (350 mg/l), and 2-days for B. mucilaginosus. While glucose (0.276 g), ferric ammonium citrate (0.047 mg/l) and 2-days were optimal conditions for P. plecoglossicida. P. plecoglossicida.and B. mucilaginosus could degrade more than 72% and 61% of PCP when these isolates were grown under a high concentration of PCP (300 and 350 mg L−1) in a mineral salt medium, respectively.

Concurrent anaerobic chromate bio-reduction and pentachlorophenol bio-degradation in a synthetic aquifer

Chromate [Cr(VI)] and pentachlorophenol (PCP) coexist widely in the environment and are highly toxic to public health. However, whether Cr(VI) bio-reduction is accompanied by PCP bio-degradation and how microbial communities can keep long-term stability to mediate these bioprocesses in aquifer remain elusive. Herein, we conducted a 365-day continuous column experiment, during which the concurrent removals of Cr(VI) and PCP were realized under anaerobic condition. This process allowed for complete Cr(VI) bio-reduction and PCP bio-degradation at an efficiency of 92.8 ± 4.2% using ethanol as a co-metabolic substrate. More specifically, Cr(VI) was reduced to insoluble chromium (III) and PCP was efficiently dechlorinated with chloride ion release. Collectively, Acinetobacter and Spirochaeta regulated Cr(VI) bio-reduction heterotrophically, while Pseudomonas mediated not only Cr(VI) bio-reduction but also PCP bio-dechlorination. The bio-dechlorinated products were further mineralized by Azospira and Longilinea. Genes encoding proteins for Cr(VI) bio-reduction (chrA and yieF) and PCP bio-degradation (pceA) were upregulated. Cytochrome c and intracellular nicotinamide adenine dinucleotide were involved in Cr(VI) and PCP detoxification by promoting electron transfer. Taken together, our findings provide a promising bioremediation strategy for concurrent removal of Cr(VI) and PCP in aquifers through bio-stimulation with supplementation of appropriate substrates.

Biotransformation of pentachlorophenol by an indigenous Bacillus cereus AOA-CPS1 isolated from wastewater effluent in Durban, South Africa.

Pentachlorophenol (PCP) is a recalcitrant biocide that bioaccumulates in the environment due to its persistent nature and has been listed as a priority pollutant due to its toxicological and health effects. In this study, a novel PCP-degrading Bacillus cereus strain AOA-CPS1 (BcAOA) was isolated from wastewater and characterized for PCP biotransformation in a batch reactor. The degradation kinetics were elucidated via substrate inhibition models, while PCP biotransformation was established by spectrophotometric and GC-MS analysis. BcAOA shared 95% sequence homology with Bacillus cereus strain XS2 and is closely related to some B. cereus strains which are previously reported to degrade PCP and other related pollutants. BcAOA degraded 74% of 350 mgl-1ofPCP within 9 days in a batch culture. The biotransformation ofPCP by BcAOA followed the first and zero-order kinetics at low and high PCP concentration, respectively, with biokinetic constants: maximum biotransformation rate (0.0996mgl-1h-1); substrate inhibition constant (723.75mgl-1); half-saturation constant (171.198mgl-1) and R2 (0.98). The genes (pcpABCDE, cytochrome P450) encoding the enzymes involved in the biodegradation of PCP were amplified from the genomic DNA of BcAOA. Further, depending upon the genes amplified and identified metabolites using GC-MS, two different PCP biotransformation pathways were proposed in this study. Cloning and expression of the catabolic genes are underway to map out the concise pathway for PCP biotransformation by BcAOA.

Microbial community response to the toxic effect of pentachlorophenol in paddy soil amended with an electron donor and shuttle

Understanding the degradation of pentachlorophenol (PCP) by indigenous microorganisms stimulated by an electron donor and shuttle in paddy soil, and the influences of PCP/electron donor/shuttle on the native microbial community are important for biodegradation and ecological and environmental safety. Previous studies focused on the kinetics and the microbial actions of PCP degradation, however, the effects of toxic and antimicrobial PCP and electron donor/shuttle on the microbial community diversity and composition in paddy soil are poorly understood. In this study, the effects of PCP, an electron donor (lactate), and the electron shuttle (anthraquinone-2, 6-disulfonate, AQDS) on the microbial community in paddy soil were investigated. The results showed that the presence of PCP reduced the microbial diversity compared to the control during PCP degradation, while increased the microbial diversity was observed in response to lactate and AQDS. The addition of PCP stimulated the microorganisms involved in PCP dechlorination, including Clostridium, Desulfitobacterium, Pandoraea, and unclassified Veillonellaceae, which were dormant in raw soil without PCP stress. In all of the treatments with PCP, the addition of lactate or AQDS enhanced PCP dechlorination by stimulating the growth of functional groups involved in PCP dechlorination and by changing the microbial community during dechlorination process. The microbial community tended to be uniform after complete PCP degradation (28 days). However, when lactate and AQDS were present simultaneously in PCP-contaminated soil, lactate acted as a carbon source or electron donor to promote the activities of microbial community, and AQDS changed the redox potential because of the production of reduced AQDS. These findings enhance our understanding of the effect of PCP and a biostimulation method for PCP biodegradation in soil ecosystems at the microbial community level, and suggest the appropriate selection of an electron donor/shuttle for accelerating the bioremediation of PCP-contaminated soils.

Dynamic processes in conjunction with microbial response to disclose the biochar effect on pentachlorophenol degradation under both aerobic and anaerobic conditions

Organochlorines are critical soil contaminants and the use of biochar has recently shown potential to improve soil remediation. However, little is known about biochar-microbe interactions nor the impact on environmental processes such as the immobilization and biodegradation of organochlorine compounds. In this study, we performed microcosm experiments to elucidate how biochar affected the biodegradation and sequestration of pentachlorophenol (PCP). Our results showed that the amendment of biochar markedly inhibited PCP biodegradation due to a strong sorption affinity for PCP under both aerobic and anaerobic conditions. Notably, the inhibitory effect was relatively weaker under anaerobic conditions than under aerobic conditions. The addition of biochar can dramatically shift the bacterial community diversity in the PCP-spiked soils. Under aerobic conditions, biochar significantly stimulated the growth of PCP-degrading bacteria Bacillus and Sphingomonas, but reduced the opportunities for microbes to contact with PCP directly. Under anaerobic conditions, the non-strict organohalide-respiring bacteria Desulfovibrio, Anaeromyxobacter, Geobacter and Desulfomonile were the main drivers of PCP transformation. Our results imply that the use of biochar as a soil remediation strategy for organochlorine compounds should be cautious.

Pentachlorophenol biodegradation in two-phase bioreactors operated with absorptive polymers: Box-Behnken experimental design and optimization by response surface methodology

The biodegradation of pentachlorophenol (PCP), the most toxic among chlorophenols, was extensively investigated in solid-liquid two-phase bioreactors (according to Box-Behnken experimental design) to demonstrate the feasibility of this technological platform. Process performance optimization for the subsequent scale up was also performed. The process was catalysed by an acclimated microbial consortium and the partitioning phase consisted of Hytrel 8206 polymer. The virtuous combination of polymer uptake/release and microbial biodegradation allowed achieving practically complete biodegradation efficiencies and rates in the range of 4.0–7.8mg/(L h) for PCP concentrations up to 100mg/L far above those previously tested. Detected biodegradation rates are one order of magnitude higher than the ones reported for suspended biomass reactors. A regression model based on 3 independent variables (initial PCP and biomass concentration and polymer-to-water ratio) was formulated to predict the volumetric biodegradation rate. The significance of independent variables and their interactions was tested by the analysis of variance (ANOVA) with 95% confidence limit. The model resulted adequate and the polymer-to-water ratio was identified as the most significant factor affecting the system response. Maximization of the biodegradation rate has been achieved for PCP concentration of 100mg/L, biomass concentration of 1 gVSS/L and polymer-to-water ratio of 9%.

Characterization of a thermostable Deconica castanella Laccase and application toward pentachlorophenol degradation

Pentachlorophenol (PCP) is an organochlorine pesticide whose toxicity led it to be banned in several countries. In Brazil however, this compound is widely accessible, and its indiscriminate use leads to extensive soil contamination, which requires henceforth, the development of new approaches to manage PCP presence in environment. Considering that PCP is susceptible to undergo enzymatic degradation, this investigation is thence, aimed at the purification, and characterization, of a thermostable fungal enzyme (i.e. Laccase of Deconica castanella (Dc-Lac), and assess its role in PCP in vitro biodegradation. Results evidenced that, molecular mass of the partially purified Dc-Lac was estimated to be of 64 kDa, presenting apparent Km of 0.47 µmol, and Vmax of 11.56 U mg−1. The optimum temperature and pH were 55 °C and 2.5, respectively. The T½ verified at 55, 60, and 80 °C were 19 and 17 hr, and 47 min, respectively. The highest PCP biodegradation was of 23% at pollutant concentration of 100 µg L−1, which evidenced that Dc-Lac is a thermostable enzyme that acted directly in PCP degradation and may be a useful asset to remediate this pollutant.

Genome-Wide Analysis of Transcriptional Changes and Genes That Contribute to Fitness during Degradation of the Anthropogenic Pollutant Pentachlorophenol by Sphingobium chlorophenolicum.

Pentachlorophenol (PCP) is a highly toxic pesticide that was first introduced in the 1930s. The alphaproteobacterium Sphingobium chlorophenolicum, which was isolated from PCP-contaminated sediment, has assembled a metabolic pathway capable of completely degrading PCP. This pathway produces four toxic intermediates, including a chlorinated benzoquinone that is a potent alkylating agent and three chlorinated hydroquinones that react with O2 to produce reactive oxygen species (ROS). RNA-seq analysis revealed that PCP causes a global stress response that resembles responses to proton motive force uncoupling and membrane disruption, while surprisingly, little of the response resembles the responses expected to be produced by the PCP degradation intermediates. Tn-seq was used to identify genes important for fitness in the presence of PCP. By comparing the genes that are important for fitness in wild-type S. chlorophenolicum and a non-PCP-degrading mutant, we identified genes that are important only when the PCP degradation intermediates are produced. These include genes encoding two enzymes that are likely to be involved in protection against ROS. In addition to these enzymes, the endogenous levels of other enzymes that protect cells from oxidative stress appear to mitigate the toxic effects of the chlorinated benzoquinone and hydroquinone metabolites of PCP. The combination of RNA-seq and Tn-seq results identify important mechanisms for defense against the toxicity of PCP. IMPORTANCE Phenolic compounds such as pentachlorophenol (PCP), triclosan, and 2,4-dichlorophenoxyacetic acid (2,4-D) represent a common class of anthropogenic biocides. Despite the novelty of these compounds, many can be degraded by microbes isolated from contaminated sites. However, degradation of this class of chemicals often generates toxic intermediates, which may contribute to their recalcitrance to biodegradation. We have addressed the stresses associated with degradation of PCP by Sphingobium chlorophenolicum by examining the transcriptional response after PCP exposure and identifying genes necessary for growth during both exposure to and degradation of PCP. This work identifies some of the mechanisms that protect cells from this toxic compound and facilitate its degradation. This information could be used to engineer strains capable of improved biodegradation of PCP or similar phenolic pollutants.

Assessment of genetic diversity and bioremediation potential of pseudomonads isolated from pesticide-contaminated artichoke farm soils.

A total of 68 dimethoate and pentachlorophenol-tolerant rhizobacteria, isolated from a pesticide-contaminated agricultural soil, have been identified and typed by means of 16S-23S rRNA internal transcribed spacers analysis (ITS-PCR), 16S rRNA gene sequencing and by repetitive extragenic palindromic (BOX-PCR). The majority of bacterial isolates (84.31%) belonged to Proteobacteria (with a predominance of Gammaproteobacteria, 72.54%), while the remaining isolates were affiliated with Firmicutes (9.80%), Bacteroidetes (1.96%) and Actinobacteria (3.92%). The pesticide-tolerant bacterial isolates belonged to 11 genera, namely Pseudomonas, Bacillus, Acinetobacter, Flavobacterium, Comamonas, Achromobacter, Rhodococcus, Ochrobactrum, Aquamicrobium, Bordetella and Microbacterium. Within the well-represented genus Pseudomonas (n = 36), the most common species was Pseudomonas putida (n = 32). The efficacy of the selected strain, Pseudomonas putida S148, was further investigated for biodegradation of pentachlorophenol (PCP) in minimal medium, when used as a sole carbon and energy source. At an initial concentration of 100mg/L, P. putida S148 degraded 91% of PCP after 7days. GC-MS analyses revealed the formation of tetrachlorohydroquinone, tri- and di-chlorophenols as biodechlorination products in PCP remediation experiments. The toxicity estimation showed that 50% lethal concentration (LC50) and 50% growth inhibition concentration (IGC50) obtained values for the major identified compounds (2,3,4,6 tetrachlorophenol, 2,3,5,6 tetrachlorophenol and tetrachlorohydroquinone) were higher than those estimated for the PCP indicating that the metabolites are less toxic than the original compound for those specific organisms. S148 strain could be added to pesticide-contaminated agricultural soils as a bacterial inoculant for its potential to improve soil quality.

Bacterial-mediated biodegradation of pentachlorophenol via electron shuttling

ABSTRACTPentachlorophenol (PCP) degradation by soil indigenous bacteria represents a practical and cost-effective solution. In the present study, bacteria isolated from paddy soil was investigated and the role of electron shuttling (ES) in the PCP degradation process was assessed. Two strains demonstrated the highest PCP degradation of 93.5% and 94.88% in the presence of citrate and were identified using 16S rRNA phylogenetic analysis as Pseudomonas chengduensis and Pseudomonas plecoglossicida, respectively. Both strains showed higher PCP degradation in free form as opposed to a reduced activity in immobilized and respiratory impaired form. The addition of pyruvate resulted in about 80% PCP degradation in 5 days for P. chengduensis, on the other hand, P. plecoglossicida showed the same result under anaerobic conditions whether pyruvate was added or not. Phenazine and the outer membrane c-type cytochrome were reported only for P. chengduensis as opposed to P. plecoglossicida. The results indicate that despite following different approaches in PCP degradation, both strains are useful in PCP clean-up under aerobic and anaerobic conditions and in free direct contact. The degradation is enhanced via ES. This is considered both an effective and feasible technology for in situ clean-up of contaminated sites or on-site bioreactors.

Effects of humic acid on pentachlorophenol biodegrading microorganisms elucidated by stable isotope probing and high‐throughput sequencing approaches

Humic substances (HSs) are ubiquitous in soil and can be reversibly oxidized and reduced by acting as redox mediators. They participate in microbial metabolism and directly affect the biodegradation of organic pollutants. However, the effects of HSs on specific microbial taxa that are responsible for the degradation of organic pollutants remain unclear. In this research, the effects of humic acids (HAs), extracted from three types of soil, forest (CBHA), paddy (PSHA) and peat (YNHA) on the microbial community involved in anaerobic mineralization of pentachlorophenol (PCP) were investigated with high‐throughput sequencing and stable isotope probing (SIP) approaches. The results showed that all HA samples accelerated the biotransformation processes of PCP; the largest rate was obtained with YNHA. Illumina sequencing revealed that Desulfovibrio and Clostridium were the dominant functional bacteria for the dechlorination of PCP. During the subsequent PCP degradation and mineralization processes, HAs affected the diversity and abundance of microbial communities, and several taxa were enriched in the 13C‐heavy fractions compared with 12C‐heavy fractions. In the absence of HA, Methanobacterium and Spartobacteria showed a significant increase in 13C‐heavy fractions. Methanosarcina and OP11 were the dominant PCP degraders in microcosms when amended with CBHA, whereas Burkholderia and Methanobacterium were the key PCP degraders in PSHA‐ and YNHA‐amended experimental microcosms. These results improve our knowledge of the diversity and ubiquitous nature of HS‐utilizing microorganisms involved in PCP degradation, providing scientific support for the development of in situ bioremediation technologies for HS‐rich soil contaminated by PCP.Highlights All humic acids facilitated biodegradation of pentachlorophenol. The greater the carbon content of HA, the greater was the rate of dechlorination. Clostridium and Desulfovibrio dominated PCP dechlorination. SIP suggested that Methanobacterium, Methanosaricina, OP11, Spartobactria and Burholderia acquired PCP‐derived carbon.

Residues His172 and Lys238 are Essential for the Catalytic Activity of the Maleylacetate Reductase from Sphingobium chlorophenolicum Strain L-1

Maleylacetate reductase (PcpE), the last enzyme in the pentachlorophenol biodegradation pathway in Sphingobium chlorophenolicum L-1, catalyzes two consecutive reductive reactions, reductive dehalogenation of 2-chloromaleylacetate (2-CMA) to maleylacetate (MA) and subsequent reduction of MA to 3-oxoadipate (3-OXO). In each reaction, one molecule of NADH is consumed. To better understand its catalytic function, we undertook a structural model-based site-directed mutagenesis and steady-state kinetics study of PcpE. Our results showed that the putative catalytic site of PcpE is located in a positively charged solvent channel at the interface of the two domains and the binding of 2-CMA/MA involves seven basic amino acids, His172, His236, His237, His241 and His251, Lys140 and Lys238. Mutagenesis studies showed that His172 and Lys238 are essential for the catalytic activity of PcpE. However, the mutation of His236 to an alanine can increase the catalytic efficiency (kcat/Km) of PcpE by more than 2-fold, implying that PcpE is still in an early stage of molecular evolution. Similar to tetrachlorobenzoquinone reductase (PcpD), PcpE is also inhibited by pentachlorophenol in a concentration-dependent manner. Furthermore, our studies showed that PcpE exhibits an extremely low but detectable level of alcohol dehalogenase activity toward ethanol and supports the notion that it is evolved from an iron-containing alcohol dehydrogenase.

Correction to: Pentachlorophenol Biodegradation by Citrobacter freundii Isolated from Forest Contaminated Soil

One of the bibliographic reference entry of this article had the author name and family name switched by mistake.

Pentachlorophenol Biodegradation by Citrobacter freundii Isolated from Forest Contaminated Soil

Environmental pollution by pentachlorophenol (PCP) is a critical concern worldwide, and microbial bioremediation could constitute an ecologically friendly solution. The main objectives of this study were at first to clarify the factors, affecting the ability and efficiency of PCP biodegradation by the bacterium isolate P6, and secondly to optimize the condition of using P6 for PCP bioremediation. The PCP mineralizing bacterium was isolated from the contaminated forest soil of Tunisia, and it was identified as Citrobacter freundii (C. freundii), by using conventional and molecular characteristics. The HPLC and spectroscopic analysis were used to investigate the PCP degradation and the biomass formation by this isolate P6. The main results showed that P6 was able to degrade or to transform more than 98 % of 640 mg/l PCP afterwards 168 h in mineral salt medium (MSM). As well, the optimal aerobic growth conditions of P6 in MSM include essentially the range of pH (4 ≤ pH ≤ 9) and of temperature (25 °C < temperature < 30 °C). The addition of glucose as extra carbon sources has an effect to enhance the PCP biodegradation. On the other side, this isolate of C. freundii is capable to remove or transform around 95.33 % of PCP added in the sterilized soil suspension supplemented with PCP and adjusted to a final concentration of around 400 mg/l during 2 weeks of incubation at 25 °C. This last result argues in favor of the use of this strain P6 of C. freundii as a microbial tool of remediation of PCP-contaminated site.

Degradation kinetics of pentachlorophenol and changes in anaerobic microbial community with different dosing modes of co-substrate and zero-valent iron

The cometabolism as a technique for enhancing biodegradation of pentachlorophenol (PCP) has been widely used, but the effect of dosing mode of growth substrates on the cometabolic degradation of PCP in an anaerobic system with and without the addition of ZVI is still not clear. In this study, the effects of dosing modes of sodium acetate as co-substrate, i.e., one-step pulse, evenly distributed pulse, and stepwise declining pulse, and zero-valent iron (ZVI) of 1 mg l−1 on pentachlorophenol (PCP) degradation and changes in anaerobic microbial community were examined in batch tests. The results indicated that the degradation kinetic constants of PCP were related to the dosing mode of co-substrate. The complete mineralization rates of PCP in the two groups with evenly distributed pulse mode and stepwise declining pulse mode were faster than the observed rates of the group with one-step pulse mode, according to the quantitative analysis of 2,3,5,6-tetrachlorophenol, 2,3,5-tetrachlorophenol, and 2,5-chlorophenol. In addition, there was a substantial change in the content of intracellular polysaccharide in the cometabolic process of the one-step pulse and stepwise declining pulse groups. Furthermore, the electron transport system (ETS) activities reached to the maximum values of 0.841 and 0.813 ug g−1 in these two groups with the addition of 1 g l−1 ZVI, respectively. Moreover, Alcaligenes (11.02%), Comamonas (14.58%), and Ralstonia (9.16%) were the dominant genera in the groups with the three co-substrate dosing modes, respectively. This study provides a new insight into achieving anaerobic cometabolic degradation of PCP with different dosing modes of co-substrate.

Enhancing pentachlorophenol degradation by vermicomposting associated bioremediation

Vermicomposting is an effective and environmentally friendly approach for soil organic contamination clean-up. This study investigated the roles and mechanisms of earthworm (Eisenia foetida) on soil pentachlorophenol (PCP) degradation with sterile and non-sterile soil-compost treatment. Limited soil PCP degradation was observed in the control and sterile compost treatments, whereas the synergetic effects of earthworm and compost contributed to the PCP biodegradation acceleration by significantly improving microbial biomass and activities. Sequence analysis and phylogentic classification of soil bacterial and fungal community structure after 42 days treatment identified the dominancy of indigenous bacterial families Pseudomonadaceae, Sphingobacteriaceae and Xanthomonadaceae, and fungal family Trichocomaceae, which were responsible for PCP biodegradation and stimulated by vermicomposting. Further investigation revealed the dominant roles of sterile compost during PCP biodegradation as the formation of humus-PCP in soil rather than neutralizing soil pH and increasing PCP availability. The mechanisms of vermicomposting include humus-PCP complex degradation, humus consumption and soil pH neutralization. This study provides a comprehensive understanding of the synergetic effect of vermicomposting on microbial community functions and PCP degradation enhancement in soils.

The key microorganisms for anaerobic degradation of pentachlorophenol in paddy soil as revealed by stable isotope probing

Pentachlorophenol (PCP) is a common residual persistent pesticide in paddy soil and has resulted in harmful effect on soil ecosystem. The anaerobic microbial transformation of PCP, therefore, has been received much attentions, especially the functional microbial communities for the reductive transformation. However, the key functional microorganisms for PCP mineralization in the paddy soil still remain unknown. In this work, DNA-based stable isotope probing (SIP) was applied to explore the key microorganisms responsible for PCP mineralization in paddy soil. The SIP results indicated that the dominant bacteria responsible for PCP biodegradation belonged to the genus Dechloromonas of the class β-Proteobacteria. In addition, the increased production of 13CH4 and 13CO2 indicated that the addition of lactate enhanced the rate of biodegradation and mineralization of PCP. Two archaea classified as the genera of Methanosaeta and Methanocella of class Methanobacteria were enriched in the heavy fraction when with lactate, whereas no archaea was detected in the absence of lactate. These findings provide direct evidence for the species of bacteria and archaea responsible for anaerobic PCP or its breakdown products mineralization and reveal a new insight into the microorganisms linked with PCP degradation in paddy soil.

Biodegradation of pentachlorophenol by marine-derived fungus Trichoderma harzianum CBMAI 1677 isolated from ascidian Didemnun ligulum

Abstract In this study, the marine-derived fungi Aspergillus sydowii DL6A, Apergillus versicolor DL5A, Cladosporium oxysporum DL5G, Fusarium proliferatum DL11A and Trichoderma harzianum CBMAI 1677 isolated from marine ascidian Didemnun ligulum were evaluated according to their growth in the presence of pentachlorophenol (PCP). The colonies were assessed in 10, 20, 30, 40 and 50 mg L−1 of PCP in a solid culture medium (3% malt). The fungus T. harzianum CBMAI 1677 showed the best growth at 50 mg L−1, which suggests its potential for biodegradation, therefore, this strain was selected for quantitative experiments in 3% malt liquid medium (initial concentration of 20 mg L−1 of PCP) using a validated method. After 7 d of incubation, PCP was not detected and an increasing concentration of pentachloroanisole (PCA) and 2,3,4,6-tetrachloroanisole (2,3,4,6-TeCA) was observed. In a second step, T. harzianum CBMAI 1677 was employed in the biodegradation of PCA and 2,3,4,6-TeCA in a liquid medium. It was observed that both PCA and 2,3,4,6-TeCA were also biodegraded. T. harzianum CBMAI 1677 is a potential strain for bioremediation studies since it was able of biodegrade not only PCP at 20 mg L−1, but also its main metabolites PCA and 2,3,4,6-TeCA.

Burkholderiales participating in pentachlorophenol biodegradation in iron-reducing paddy soil as identified by stable isotope probing.

As the most prevalent preservative worldwide for many years, pentachlorophenol (PCP) has attracted much interest in the study of biodegradation in soil and aquatic ecosystems. However, the key microorganisms involved in anaerobic degradation are less well understood. Hence, we used DNA-based stable isotope probing (SIP) to identify the PCP-degrading microorganisms in iron-rich paddy soil under anaerobic conditions. (12)C- and (13)C-labeled PCP were almost completely degraded in 30 days under iron-reducing conditions. The results of terminal restriction fragment length polymorphism (T-RFLP) of 16S rRNA genes showed that 197 and 217 bp (HaeIII digests) restriction fragments (T-RFs) were enriched in heavy DNA fractions of (13)C-labeled samples, and the information from 16S rRNA gene clone libraries suggested that the microorganisms corresponding to these T-RF fragments, which increased in relative abundance during incubation, belonged to the order of Burkholderiales, in which 197 and 217 bp were classified as unclassified Burkholderiales and the genus Achromobacter, respectively. The results of the present study indicated that Burkholderiales-affiliated microorganisms were responsible for PCP degradation in anaerobic paddy soil and shed new light on in situ bioremediation in anaerobic PCP contaminated soil.