Mineralization of mono- and dichlorobenzenes and simultaneous degradation of chloro- and methyl-substituted benzenes by the white rot fungus Phanerochaete chrysosporium

Biodegradation of microplastics derived from controlled release fertilizer coating: Selective microbial colonization and metabolism in plastisphere

Coated controlled-release fertilizers (CRFs) are widely used in agriculture, and the persistent presence of residual polymer coating has raised environmental concerns. This study investigates the underlying degradation dynamics of microplastics (MPs) derived from three typical materials used in CRFs, including polyethylene (PE), epoxy (EP), and polyurethane (PU), through a soil degradation test. The formation of surface biofilm, the succession process, and metabolic characteristics of microbial community are revealed by laser scanning confocal microscope, 16S rRNA sequencing, and non-targeted metabolomics analysis. The weight loss rates of PE, EP, and PU after 807 days of degradation were 16.70 %, 2.79 %, and 4.86 %, respectively. Significant secondary MPs were produced with tears and holes appeared in the coating cross sections and pyrolysis products were produced such as ethers, acids, and esters for PE; alkanes, olefins and their branched-chain derivatives for EP; and short-chain fatty acids and benzene molecules for PU. The coating surface selectively recruited the bacteria of Chujaibacter and Ralstonia and fungus of Fusarium and Penicillium, forming biofilm composed of lipids, proteins, and living cells. The metabolism of amino acids and polymers was enhanced to protect against MP-induced stress. The metabolites or intermediates of organic acids and derivatives, oxygen-contained organic compounds, and benzenoids on CRF surface increased significantly compared with soil, but there were no significant differences among different coating types. This study provides insights to the underlying mechanisms of biodegradation and microenvironmental changes of MPs in soil.

Myco- and phyco-remediation of polychlorinated biphenyls in the environment: a review

Polychlorinated biphenyls (PCBs) are toxic organic compounds and pose serious threats to environment and public health. PCBs still exist in different environments such as air, water, soil, and sediments even on ban. This review summarizes the phyco- and myco-remediation technologies developed to detoxify the PCB-polluted sites. It was found that algae mostly use bioaccumulation to biodegradation strategies to reclaim the environment. As bio-accumulator, Ulva rigida C. Agardh has been best at 25 ng/g dry wt to remove PCBs. Evidently, Anabaena PD-1 is the only known PCB degrading alga and efficiently degrade Aroclor 1254 and dioxin-like PCBs up to 84.4% and 37.4% to 68.4%, respectively. The review suggested that factors such as choice of algal strains, response of microalgae, biomass, the rate of growth, and cost-effective cultivation conditions significantly influence the remediation of PCBs. Furthermore, the Anabaena sp. linA gene of Pseudomonas paucimobilis Holmes UT26 showed enhanced efficiency. Pleurotus ostreatus (Jacq.) P. Kumm is the most efficient PCB degrading fungus, degrading up to 98.4% and 99.6% of PCB in complex and mineral media, respectively. Combine metabolic activities of bacteria and yeast led to the higher detoxification of PCBs. Fungi-algae consortia would be a promising approach in remediation of PCBs. A critical analysis on potentials and limits of PCB treatment through fungal and algal biosystems have been reviewed, and thus, new insights have emerged for possible bioremediation, bioaccumulation, and biodegradation of PCBs.

Application of immobilized mycelium-based pellets for the removal of organochlorine compounds: a review

Organochlorines have diverse structures and applications and are included in the list of persistent organic pollutants (POPs) due to their toxicity and environmental persistence. The reduced capacity of conventional wastewater treatment plants to remove these compounds encourages the development of cost-effective and efficient remediation approaches. Fungal biotechnology can contribute to the development of these technologies through their enzymatic machinery but faces several drawbacks related to the use of dispersed mycelium. In this sense, investigations concerning the degradation of organochlorines using immobilized fungi demonstrated an increase in contaminant removal efficiency compared with degradation by free cells. Despite this interest, the mechanisms of immobilized fungi have not been comprehensively reviewed. In this paper, recent advances of laboratory and field studies in organochlorine compounds removal by fungi are reviewed, focusing on the role of immobilization techniques. Firstly, the mechanisms of organochlorines bioconversion by fungi and the factors affecting enzyme activity are elucidated and discussed in detail. Then, the main targeted compounds, fungi, technics, and materials used for immobilization are discussed, as well as their advantages and limitations. Furthermore, critical points for future studies of fungi immobilization for organochlorine removal are proposed.

Characterization of 2,3,7,8-tetrachlorodibenzo-p-dioxin biodegradation by extracellular lignin-modifying enzymes from ligninolytic fungus

Ligninolytic fungi secrete extracellular lignin-modifying enzymes (LME) that degrade plant polymers for fungal nutrition but that are, because of their broad substrate specificity, also applicable for the degradation of many hazardous pollutants. Laccase is one of the most well characterized LME and is involved in the removal and degradation of recalcitrant aromatic compounds with or without the assistance of laccase-mediators. The Ligninolytic fungus Rigidoporus sp. FMD21 can degrade 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) with a half-life of 6.2 days. Using Rigidoporus sp. FMD21 crude extracellular enzyme extract (ExE) that mainly consisted of laccase, 77.4% of 2,3,7,8-TCDD was degraded within 36 days. The degradation rate did not depend on the 2,3,7,8-TCDD concentration in the tested range between 0.005 and 0.5 pgTEQ/μL. 2,3,7,8-TCDD was analysed by DR-CALUX® bioassay and the degradation was confirmed by GC-HRMS. In this study, we found evidence for cleavage of the diaryl ether bond in the 2,3,7,8-TCDD molecule and here we propose a new degradation mechanism in which 3,4-dichlorophenol is the main metabolite of 2,3,7,8-TCDD degradation by FMD21's ExE. Six laccase-mediators were tested. Three of them 1-hydroxybenzotriazole (HBT), syringaldehyde (Syr) and violuric acid (Vio) showed an equipotent added effect on 2,3,7,8-TCDD degradation by ExE, however only in case of Vio a level of significance was reached. The others showed no effect or negatively impacted degradation. In conclusion, we have shown that Rigidoporus sp. FMD21 produces extracellular enzymes, mainly laccases that apparently are able to degrade the highly recalcitrant and most toxic 2,3,7,8-congener of TCDD via diaryl bond cleavage into 3,4-dichlorophenol.

Mesoporous SnMgNd substituted M-hexaferrite catalyzed heterogeneous photo-Fenton-like activity for degradation of methylene blue

Emerging pollutants and industrial waste dyes are significantly increasing with the development of new industries. The development of nano-composites are getting more attention in this regard due to their unique properties. Here in barium M-hexaferrites with novel composition BaFe₁₁(SnMg)_0.25Nd_0.5O₁₉ (SMN) was synthesized as heterogeneous photo-Fenton-like system for the degradation of Methylene Blue (MB). The synthesized SMN nano-particles (NPs) were characterized with numerous techniques, including Thermo-gravimetric analysis (TGA), X-ray Diffraction (XRD), Brunauer-Emmet-Teller (BET), Transmission Electron Microscopy (TEM), Scanning electron microscopy (SEM), Optical properties (UV), Fourier transform infrared spectra (FTIR) and magnetometer (VSM). The factors affecting the degradation reaction such as photocatalyst (SMN) dosage, H₂O₂ concentrations, UV irradiation and pH were scientifically explored. The photo-Fenton-like activity of SMN-NPs revealed high degradation (98.89%) and mineralization (83%) after 140 min in SMN-NPs + H₂O₂ + UV irradiation system within a wide range of pH. Moreover, good stability and recycling ability of SMN-NPs was achieved. HPLC/GC-MS analysis revealed the degradation pathways of MB and the intermediates were mineralized into CO₂ and H₂O. The outcomes revealed that SMN-NPs were promising for emerging industrial dyes removal.

Mycoremediation of PCBs by Pleurotus ostreatus: Possibilities and Prospects

With the rising awareness on environmental issues and the increasing risks through industrial development, clean up remediation measures have become the need of the hour. Bioremediation has become increasingly popular owing to its environmentally friendly approaches and cost effectiveness. Polychlorinated biphenyls (PCBs) are an alarming threat to human welfare as well as the environment. They top the list of hazardous xenobiotics. The multiple effects these compounds render to the niche is not unassessed. Bioremediation does appear promising, with myco remediation having a clear edge over bacterial remediation. In the following review, the inputs of white-rot fungi in PCB remediation are examined and the lacunae in the practical application of this versatile technology highlighted. The unique abilities of Pleurotus ostreatus and its deliverables with respect to removal of PCBs are presented. The need for improvising P. ostreatus-mediated remediation is emphasized.

Ligninase-mediated transformation of 4,4'-dibromodiphenyl ether (BDE 15)

The structurally related hydroxylated polybrominated diphenyl ether (PBDE) like hydroxylated 4,4'-dibromodiphenyl ether widely occur in precipitation, surface water, and biotic media. The origins of hydroxylated PBDEs (OH-PBDEs) are of particular interest due to their greater toxic potencies than the corresponding PBDEs. We studied the transformation behavior and products of 4,4'-dibromodiphenyl ether (BDE 15) mediated by lignin peroxidase (LiP), an extracellular enzyme that is produced by certain white rot fungus and is widely present in the natural environment. We found that BDE 15 can be effectively transformed through the reaction mediated by LiP, and two different mono-OH-dibromodiphenyl ethers were identified by using gas chromatography-mass spectrometry (GC-MS) and GC-MS/MS. In particular, we compared the reaction behavior for systems variously containing natural organic matter (NOM) and/or veratryl alcohol (VA), a metabolite that certain fungus produces along with LiP in nature. It was found that the VA's enhancement effect on LiP performance was impaired by the presence of NOM. The findings in this study provide useful information for better understanding the origins of OH-PBDEs found in the environment.

P450 monooxygenases (P450ome) of the model white rot fungus Phanerochaete chrysosporium

Phanerochaete chrysosporium, the model white rot fungus, has been the focus of research for the past about four decades for understanding the mechanisms and processes of biodegradation of the natural aromatic polymer lignin and a broad range of environmental toxic chemicals. The ability to degrade this vast array of xenobiotic compounds was originally attributed to its lignin-degrading enzyme system, mainly the extracellular peroxidases. However, subsequent physiological, biochemical, and/or genetic studies by us and others identified the involvement of a peroxidase-independent oxidoreductase system, the cytochrome P450 monooxygenase system. The whole genome sequence revealed an extraordinarily large P450 contingent (P450ome) with an estimated 149 P450s in this organism. This review focuses on the current status of understanding on the P450 monooxygenase system of P. chrysosproium in terms of pre-genomic and post-genomic identification, structural and evolutionary analysis, transcriptional regulation, redox partners, and functional characterization for its biodegradative potential. Future research on this catalytically diverse oxidoreductase enzyme system and its major role as a newly emerged player in xenobiotic metabolism/degradation is discussed.

Degradation of 2-chlorotoluene by Rhodococcus sp. OCT 10

A strain Rhodococcus sp. OCT 10 DSM 45596(T), exhibiting 99.9% of 16S rDNA identity with Rhodococcus wratislaviensis NCIMB 13082, was isolated from a soil sample. The strain completely mineralised 2-chlorotoluene, 2-bromotoluene, o-xylene, benzyl alcohol and benzoate. In contrast, 2-fluorotoluene was only partially mineralised. By GC-MS and (1)H-NMR analyses, 4-chloro-3-methylcatechol was identified as the central intermediate in the degradation pathway of 2-chlorotoluene. It was further degraded by enzymes of the meta cleavage pathway. Catechol 1,2-dioxygenase and chlorocatechol 1,2-dioxygenase as the initial enzymes of the ortho cleavage pathways were not detectable under these conditions. Furthermore, neither formation nor oxidation of 2-chlorobenzylic alcohol, 2-chlorobenzaldehyde, or 2-chlorobenzoate was observed, thereby excluding side chain oxidation activity.

Stimulative effects of ozone on a biofilter treating gaseous chlorobenzene

Recalcitrant volatile organic compounds with low biodegradabilities pose challenges for biofiltration technologies. In this study, the effects and mechanism of adding ozone on the performance of a biofilter were investigated. A biofilter treating chlorobenzene was set up and operated continuously for 265 days under different inlet ozone concentrations. Results showed that ozone below 120 mg m(-3) could notably enhance the biofilter performance. The average chlorobenzene removal efficiency increased from 40 to 70% and then to 90% while the inlet ozone concentration rose from 0 to 40 mg m(-3) and 120 mg m(-3). Reducing ozone concentration resulted in a decrease in removal efficiency from 90 to 40%. Further analysis indicated that the thickness and extra-cellular polymer substance content of the biofilm were remarkably reduced while inlet ozone concentration was gradually increased. Meanwhile, the specific surface areas of the filter bed were found to increase from 784 to 820 and 880 m(2) m(-3). A respiratory quinone profile showed that the dominant quinone shifted from ubiquinone-8 to menaquinone-9(H(2)) after ozone was added. This indicated that some Gram-positive bacteria with thick cell wall became the dominant species under ozone compression.

Dechlorination of 1,2,3- and 1,2,4-trichlorobenzene by the white-rot fungus Trametes versicolor

The degradation of 1,2,3-, 1,3,5- and 1,2,4-trichlorobenzene (TCB) by the white-rot fungus Trametes versicolor was studied. Time course experiments showed a degradation rate of 2.27 and 2.49 nmol d(-1)mg(-1) dry weight of biomass during the first 4d of incubation in cultures spiked with 6 mg L(-1) of 1,2,3- and 1,2,4-TCB, respectively. A high percent of degradation of 91.1% (1,2,3-TCB) and 79.6 (1,2,4-TCB) was obtained after 7d. However, T. versicolor was not able to degrade 1,3,5-TCB under the conditions tested. For a range of concentrations of 1,2,4-TCB between 6.5 and 23 mg L(-1), a complete dechlorination of the molecule was observed. Cytochrome P450 monooxygenase appears to be involve in the first step of 1,2,4-TCB degradation, as evidenced by marked inhibition of both dechlorination and degradation of 1,2,4-TCB in the presence of the known cyt P450 inhibitors 1-aminobenzotriazole and piperonyl butoxide. Four intermediates formed from 1,2,4-TCB degradation were detected the second day of incubation, which did not appear the seventh day: 2,3,5-trichloromuconate, its corresponding carboxymethylenebutenolide, 2- or 5-chloro-4-oxo-2-hexendioic acid and 2- or 5-chloro-5-hydroxy-4-oxo-2-pentenoic acid. Based on these results, a degradation pathway of 1,2,4-TCB through cyt P450 monooxygenase and epoxide hydrolase was proposed.

Biodegradation of gaseous chlorobenzene by white-rot fungus Phanerochaete chrysosporium

OBJECTIVE

To evaluate the effect of white rot fungus Phanerochaete chrysosporium on removal of gaseous chlorobenzene.

METHODS

Fungal mycelium mixed with a liquid medium was placed into airtight bottles. A certain amount of chlorobenzene was injected into the headspace of the bottles under different conditions. At a certain interval, the concentrations in the headspace were analyzed to evaluate the degradation of chlorobenzene by P. chrysosporium.

RESULTS

The degradation effects of P. chrysosporium on chlorobenzene under different conditions were investigated. The difference in the optimum temperature for the growth of the fungi and chlorobenzene degradation was observed. The data indicated that a lower temperature (28 degrees C) would promote the degradation of chlorobenzene than the optimum temperature for the growth of the fungi (37 degrees C). A low nitrogen source concentration (30 mg N/L) had a better effect on degrading chlorobenzene than a high nitrogen source concentration (higher than 100 mg N/L). A high initial concentration (over 1100 mg/m3) of chlorobenzene showed an inhibiting effect on degradation by P. chrysosporium. A maximum removal efficiency of 95% was achieved at the initial concentration of 550 mg/m3.

CONCLUSION

P. chrysosporium has a rather good ability to remove gaseous chlorobenzene. A low nitrogen source concentration and a low temperature promote the removal of chlorobenzene by P. chrysosporium. However, a high initial chlorobenzene concentration can inhibit chlorobenzene degradation.

Chemical identification and acute biotoxicity assessment of gaseous chlorobenzene photodegradation products

In order to evaluate the ecological safety and feasibility of UV photodegradation processes for the treatment of halogenated aromatic hydrocarbons, the chemical composition and acute biotoxicity of gaseous chlorobenzene photodegradation products were investigated. Results showed that the main products of chlorobenzene photodegradation included hydrochloric acid, acetic acid, formic acid, phenol and chlorophenol. Roughly 64% of the removed chlorobenzene was converted into phenol, making it the most significant product formed. The types of byproducts suggested that two distinct reaction pathways might compete during the photodegradation process. Interestingly, it appeared that one of these pathways did not involve the direct photocatalytic oxidation of chlorobenzene. An acute biotoxicity assay measuring the inhibition of bioluminescence indicated that gaseous exhaust with overall higher toxicity was emitted after UV irradiation. The acute toxicity of the UV reactor exhaust gas was as high as EC(50)=13.5mg-Zn(2+)m(-3-)-gas. The increased toxicity mainly resulted from the conversion of chlorobenzene to more soluble toxic products and ozone production during the photodegradation process.

Ex-situ bioremediation of chlorobenzenes in soil

Chlorinated benzenes, including chlorobenzene (CB) and 1,2-dichlorobenzene (DCB) are widely used as chemical intermediates and solvents across industry. Soil contaminated with these compounds was treated in a pilot-scale trial in 6 m3 cells. Air was drawn through each cell and exhausted via an activated carbon (GAC) filter system. The trial objective was to stimulate native microflora with nutrients and varying levels of organic amendments (0%, 12% and 35%). Initial soil DCB concentrations varied from <1 to 6 mg/kg in the three cells with an average of 2 mg/kg. Approximately 90% of the DCB mass present in the soil was removed over a period of 2-3 weeks. Up to 100-fold increases in total heterotrophs (THP), CB+ and DCB+ degraders were observed. Residual concentrations of chlorinated benzenes were generally below detection limits (0.2 mg/kg). Adding organic matter did not enhance the removal of CB and DCB under the trial conditions, which were set up to minimize losses from volatilization. Biodegradation estimation calculations indicated that <5% of the chlorinated benzenes were removed by volatilization and 90% removed by biodegradation. Laboratory shake flask trials confirmed that the soils in the pilot-scale treatment contained a microbial consortium capable of mineralizing CB and DCB. This consortium was capable of mineralizing both CB and DCB with up to 50% of carbon added as chlorinated benzene substrate being recovered as CO2 and up to 44% of organic chlorine being released as chloride ion in mineralization tests, further confirming these chlorinated benzenes were biodegraded. The study confirms that vented ex-situ biotreatment processes for chlorinated benzenes can be achieved without excessive losses from volatilization and that naturally occurring microflora can be readily stimulated with aeration and nutrients.

Microbial degradation of chlorinated benzenes

Chlorinated benzenes are important industrial intermediates and solvents. Their widespread use has resulted in broad distribution of these compounds in the environment. Chlorobenzenes (CBs) are subject to both aerobic and anaerobic metabolism. Under aerobic conditions, CBs with four or less chlorine groups are susceptible to oxidation by aerobic bacteria, including bacteria (Burkholderia, Pseudomonas, etc.) that grow on such compounds as the sole source of carbon and energy. Sound evidence for the mineralization of CBs has been provided based on stoichiometric release of chloride or mineralization of (14)C-labeled CBs to (14)CO(2). The degradative attack of CBs by these strains is initiated with dioxygenases eventually yielding chlorocatechols as intermediates in a pathway leading to CO(2) and chloride. Higher CBs are readily reductively dehalogenated to lower chlorinated benzenes in anaerobic environments. Halorespiring bacteria from the genus Dehalococcoides are implicated in this conversion. Lower chlorinated benzenes are less readily converted, and mono-chlorinated benzene is recalcitrant to biotransformation under anaerobic conditions.

Biomineralisation of 1,2,4-trichlorobenzene in soils by an adapted microbial population

In laboratory experiments the mineralisation of 14C-labelled 1,2,4-trichlorobenzene (1,2,4-TCB) in soils was studied by direct measurement of the evolved 14CO2. The degradation capacity of the indigenous microbial population was investigated in an agricultural soil and in a soil from a contaminated site. Very low mineralisation of 1% within 23 days was measured in the agricultural soil. Whereas in the soil from the contaminated site the mineralisation occurred very fast and in high rates; up to 62% of the initially applied amount of 1,2,4-TCB were mineralised within 23 days. The transfer of the adapted microbial population into the agricultural soil significantly enhanced the mineralisation of 1,2,4-TCB in this soil, reflecting, that the transferred microbial population survived and maintained its degradation ability in the new microbial ecosystem. Additional nutrition sources ((NH4)2HPO4) increased the mineralisation rates in the first days significantly in the contaminated soil. In the soil from the contaminated site high amounts of non extractable 14C-residues were formed.

Sulfur tuft and turkey tail: biosynthesis and biodegradation of organohalogens by Basidiomycetes

Chlorinated aliphatic and aromatic compounds are generally considered to be undesirable xenobiotic pollutants. However, the higher fungi, Basidiomycetes, have a widespread capacity for organohalogen biosynthesis. Adsorbable organic halogens (AOX) and/or low-molecular-weight halogenated compounds are produced by Basidiomycetes of 68 genera from 20 different families. Most of the 81 halogenated metabolites identified from Basidiomycetes to date are chlorinated, although brominated and iodated metabolites have also been described. Two broad categories of Basidiomycete organohalogen metabolites are the halogenated aromatic compounds and the haloaliphatic compounds. Some of these organohalogen metabolites have demonstrable physiological roles as antibiotics and as metabolites involved in lignin degradation. Basidiomycetes produce large amounts of low-molecular-weight organohalogens or adsorbable organic halogens (AOX) when grown on lignocellulosic substrates. In our view, Basidiomycetes, as decomposers of forest litter, are a major source of natural organohalogens in terrestrial environments. Basidiomycetes are also potent degraders of a wide range of chlorinated pollutants, such as bleachery effluent from kraft mills and pentachlorophenol, polychlorinated dioxins, and polychlorinated biphenyls. The extracellular, lignin-degrading enzymes of the Basidiomycetes are involved in the oxidative degradation of chlorophenols and dioxin and can cause reductive dechlorination of halomethanes. There is no clear-cut separation between "polluters" and "clean-uppers" within the Basidiomycetes. Several genera, e.g. Bjerkandera, Hericium, Phlebia, and Trametes, produce significant amounts of chlorinated compounds but are also highly effective in metabolizing or biotransforming chlorinated pollutants.

Degradation of polychlorinated biphenyl mixtures (Aroclors 1242, 1254, and 1260) by the white rot fungus Phanerochaete chrysosporium as evidenced by congener-specific analysis

Evidence for substantial degradation of polychlorinated biphenyl mixtures Aroclor 1242, 1254, and 1260 by the white rot fungus Phanerochaete chrysosporium, based on congener-specific gas chromatographic analysis, is presented. Maximal degradation (percent by weight) of Aroclors 1242, 1254, and 1260 was 60.9, 30.5, and 17.6%, respectively. Most of the congeners in Aroclors 1242 and 1254 were degraded extensively both in low-N (ligninolytic) as well as high-N (nonligninolytic) defined media. Even more extensive degradation of the congeners was observed in malt extract medium. Congeners with varying numbers of ortho, meta, and para chlorines were extensively degraded, indicating relative nonspecificity for the position of chlorine substitutions on the biphenyl ring. Aroclor 1260, which has not been conclusively shown to undergo aerobic microbial degradation, was shown to undergo substantial net degradation by P. chrysosporium. Maximal degradation of Aroclor 1260 was observed in malt extract medium (18.4% on a molar basis), in which most of the individual congeners were degraded.