Degradation and detoxification of the triphenylmethane dye malachite green catalyzed by crude manganese peroxidase from Irpex lacteus F17

Kinetics of dye decolorization using heterogeneous catalytic system with immobilized Achromobacter xylosoxidans DDB6

Textile effluents containing toxic dyes must be treated effectively before discharge to prevent adverse environmental impacts. Traditional physical and chemical treatment methods are costly and generate secondary pollutants. In contrast, biological treatment is a more suitable, clean, versatile, eco-friendly, and cost-effective technique for treating textile effluent. It is well established that indigenous microbial populations present in effluents can effectively degrade toxic dyes. In this regard, Achromobacter xylosoxidans DDB6 was isolated from the effluent sample to decolorize crystal violet (CV), Coomassie brilliant blue (CBB), and alizarin red (AR) by 67.20%, 28.58%, and 20.41%, respectively. The growth parameters of A. xylosoxidans DDB6 in media supplemented with 100 ppm of various dyes were determined using the modified Gompertz growth model. The immobilized cells in calcium alginate beads showed apparent decolorization rate constant of 0.27, 0.18, and 0.13 h-1 for CV, CBB, and AR, respectively. The immobilized cells in a packed bed reactor with an optimum flow rate of 0.5 mL/min were used to treat 100 ppm of CV with a percentage decolorization of 79.47% after three cycles. Based on the findings, A. xylosoxidans DDB6 could be effectively used for decolorization of various dyes.

Decolorization and detoxication of malachite green by engineered Saccharomyces cerevisiae expressing novel thermostable laccase from Trametes trogii

Malachite Green (MG) is a widely used industrial dye that is hazardous to health. Herein, the decolourisation and detoxification of MG were achieved using the engineered Saccharomyces cerevisiae expressing novel thermostable laccase lcc1 from Trametes trogii. The engineered strain RCL produced a high laccase activity of 121.83 U L-1. Lcc1 was stable at temperatures ranging from 20 ℃ to 60 ℃ and showed a high tolerance to organic solvents. Moreover, Lcc1 could decolorize different kinds of dyes (azo, anthraquinone and triphenylmethane), among which, the decolorization ability of MG is the highest, reaching 95.10 %, and the decolorization rate of other triphenylmethane dyes also over 50 %. The RCL decolorized about 95 % of 50 mg L-1 of MG dye in 10 h at 30 ℃. The MG degradation products were analyzed. The industrial application potential of the RCL was evaluated by treating industrial wastewater and the decolourisation rates were over 90 %.

Biodegradation of malachite green by Pleurotus eryngii: a study on decolorization, mechanism, toxicity, and enzyme

The purpose of this study was to investigate the biodegradation of malachite green (MG) by Pleurotus eryngii via decolorization. This study also explored the possible mechanisms and toxicity. The results indicated that this fungus exhibited strong decolorizing potential. MG degradation based on UPLC-TOF-Triple-MS analysis revealed the formation of intermediates such as 4-(dimethylamino)benzophenone, 4-(methylamino)benzophenone, and 4-(dimethylamino)phenol. Furthermore, a significant reduction in the toxicity of the degradation products was observed using the zebrafish animal model. A newly discovered dye-decolorizing peroxidase (DyP-PE) from P. eryngii was amplified, cloned, and expressed. The purified 56.4 kDa DyP-PE strongly decolorized MG, suggesting potentially application in the bioremediation of MG pollution. Thus, the DyP-PE derived from P. eryngii may contribute to the degradation of MG.

A bacterial cold-active dye-decolorizing peroxidase from an Antarctic Pseudomonas strain

DyP (dye-decolorizing peroxidase) enzymes are hemeproteins that catalyze the H₂O₂-dependent oxidation of various molecules and also carry out lignin degradation, albeit with low activity. We identified a dyp gene in the genome of an Antarctic cold-tolerant microbe (Pseudomonas sp. AU10) that codes for a class B DyP. The recombinant protein (rDyP-AU10) was produced using Escherichia coli as a host and purified. We found that rDyP-AU10 is mainly produced as a dimer and has characteristics that resemble psychrophilic enzymes, such as high activity at low temperatures (20 °C) when using 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid (ABTS) and H₂O₂ as substrates, thermo-instability, low content of arginine, and a catalytic pocket surface larger than the DyPs from some mesophilic and thermophilic microbes. We also report the steady-state kinetic parameters of rDyP-AU10 for ABTS, hydroquinone, and ascorbate. Stopped-flow kinetics revealed that Compound I is formed with a rate constant of (2.07 ± 0.09) × 10⁶ M^-1 s^-1 at pH 5 and that this is the predominant species during turnover. The enzyme decolors dyes and modifies kraft lignin, suggesting that this enzyme may have potential use in bioremediation and in the cellulose and biofuel industries. KEY POINTS: • An Antarctic Pseudomonas strain produces a dye-decolorizing peroxidase. • The recombinant enzyme (rDyP-AU10) was produced in E. coli and purified. • rDyP-AU10 showed high activity at low temperatures. • rDyP-AU10 is potentially useful for biotechnological applications.

Biocatalytic degradation of reactive blue 221 and direct blue 297 dyes by horseradish peroxidase immobilized on iron oxide nanoparticles with improved kinetic and thermodynamic characteristics

In present study, we describe the biodegradation of direct blue (DB) 297 and reactive blue (RB) 221 by immobilizing horseradish peroxidase (HRP) isolated from fresh leaves of Moringa Oliefera on iron oxide nanoparticles. Iron oxide nanoparticles were synthesized by co-precipitation method and showed a maximum immobilization efficiency of 87%. The surface topography of iron oxide nanoparticles was envisaged by scanning electron microscopy (SEM), results showed that magnetic nanoparticles (MNPs) were in the form of aggregates having size of 1 μm. Furthermore, immobilization was confirmed via functional group identification performed by Fourier transformed infrared spectroscopy (FTIR). Immobilization phenomena displaced the optimum temperature from 35 °C to 50 °C moreover, pH optima were altered from 5.0 to 7.0. Vmax and Km for free and immobilized HRP, were 303 U/mg and 1.66 mM and 312 U/mg and 1.94 mM, respectively. Enzymatic thermodynamic measurements (ΔH*, ΔS*, Ea, ΔG*) were also evaluated for immobilized HRP and its free counterpart. Optimum degradation of reactive blue (RB) and direct blue (DB) 297 with free and immobilized HRP was observed at pH 5 and at temperature 40 °C respectively. The removal efficiency of DB 297 and RB 221 with free HRP was 75% and 86% while with immobilized HRP was 81% and 92% respectively. Furthermore, biodegradation of reactive blue (RB) 221 and direct blue (DB) 297 with immobilized and free biocatalyst was also investigated by Fourier transform infrared spectroscopy (FTIR) by identification of groups involved in dye degradation. FTIR results confirmed the 100% degradation of dyes. Immobilized HRP retained significant catalytic activity after five consecutive cycles of dye degradation. In conclusion, Fe3O4 nanoparticles are promising and environmentally friendly media for enzyme immobilization. Moreover, immobilized HRP showed more thermal stability, pH stability and higher dye degradation efficiency as compared to free HRP. Furthermore, the immobilized HRP, economically more convenient and easily removable from reaction media. Owing to its thermal stability, ease of separation from reaction media and reusability, the magnetically separatable immobilized HRP can be exploited successfully for treatment of dye contaminated textile effluents.

Bioremoval and Detoxification of the Anticancer Drug Mitoxantrone Using Immobilized Crude Versatile Peroxidase (icVP/Ba) Bjerkandera adusta CCBAS 930

The aim of this study was to evaluate the biodecolorization and detoxification of the anticancer drug mitoxantron (MTX) by immobilized crude versatile peroxidase of Bjerkandera adusta CCBAS 930 (icVP/Ba). The concentrated crude VP was obtained from B. adusta CCBAS 930 culture on medium with MTX (µg/mL) addition, immobilized with 4% sodium alginate. MTX removal degree (decolorization), levels of phenolic compounds and free radicals were determined during MTX biotransformation. Moreover, the phytotoxicity (Lepidium sativum L.), biotoxicity (multi-species microbial assay, MARA), and genotoxicity (SOS Chromotest) of MTX were evaluated before and after the biological treatment. The use of icVP/Ba (95 U/mL) significantly shortened the bioremoval of 10 µg/mL MTX (95.57% after 72 h). MTX removal by icVP/Ba was correlated with an 85% and 90% decrease in the levels of phenolic compounds and free radicals, respectively. In addition, the use of icVP/Ba contributed to a decrease in the phyto-, bio-, and genotoxicity of MTX. This is the first study to describe the possibility of removing MTX using immobilized crude fungal peroxidase.

Optimization of the decolorization conditions of Rose Bengal by using Aspergillus niger TF05 and a decolorization mechanism

Aspergillus niger TF05 was applied to decolorize Rose Bengal dye. The effects of carbon source, nitrogen source, metal ion and spore concentration on Rose Bengal treatment with A. niger TF05 were studied. A Plackett–Burman design (PBD) and a uniform design (UD) were used to optimize the decolorization conditions of A. niger TF05 and enhance its decolorization effect. The mechanism of Rose Bengal decolorization by A. niger TF05 was examined by analysing degradation products via UV–visible light spectroscopy, IR spectroscopy and GC-MS. The best decolorization effect was achieved in the single factor test with glucose and ammonium chloride as carbon and nitrogen sources, respectively. Mg²⁺ was an essential ion that could improve the mould ball state and adsorption efficiency if the spore concentration was maintained at 10⁶ spores ml^–1. The optimal decolorization conditions obtained using the PBD and UD methods were 11.5 g l⁻¹ glucose, 6.5 g l⁻¹ ammonium chloride, 0.4 g l⁻¹ magnesium sulphate, pH 5.8, 28 °C, 140 r.p.m. rotational speed, 0.18 g l⁻¹ dye concentration, 0.5 ml of inocula and 120 h decolorization time. Under these conditions, the maximum decolorization rate was 106%. Spectral analysis suggested that the absorption peak of the product changed clearly after decolorization; GC-MS analysis revealed that the intermediate product tetrachlorophthalic anhydride formed after decolorization. The combined use of the PBD and UD methods can optimize multi-factor experiments. A. niger TF05 decolorized Rose Bengal during intracellular enzymatic degradation after adsorption.

Biological remediation technologies for dyes and heavy metals in wastewater treatment: New insight

The pollution of the environment caused by dyes and heavy metals emitted by industries has become a worldwide problem. The development of efficient, environmentally acceptable, and cost-effective methods of wastewater treatment containing dyes and heavy metals is critical. Biologically based techniques for treating effluents are fascinating since they provide several benefits over standard treatment methods. This review assesses the most recent developments in the use of biological based techniques to remove dyes and heavy metals from wastewater. The remediation of dyes and heavy metals by diverse microorganisms such as algae, bacteria, fungi and enzymes are depicted in detail. Ongoing biological method's advances, scientific prospects, problems, and the future prognosis are all highlighted. This review is useful for gaining a better integrated view of biological based wastewater treatment and for speeding future research on the function of biological methods in water purification applications.

Engineering globins for efficient biodegradation of malachite green: two case studies of myoglobin and neuroglobin

Engineered globins such as H64D Mb and A15C/H64D Ngb were efficient in the degradation of malachite green, with activities much higher than those of some native enzymes.

The Manganese Peroxidase Gene Family of Trametes trogii: Gene Identification and Expression Patterns Using Various Metal Ions under Different Culture Conditions

Manganese peroxidases (MnPs), gene family members of white-rot fungi, are necessary extracellular enzymes that degrade lignocellulose and xenobiotic aromatic pollutants. However, very little is known about the diversity and expression patterns of the MnP gene family in white-rot fungi, especially in contrast to laccases. Here, the gene and protein sequences of eight unique MnP genes of T. trogii S0301 were characterized. Based on the characteristics of gene sequence, all TtMnPs here belong to short-type hybrid MnP (type I) with an average protein length of 363 amino acids, 5–6 introns, and the presence of conserved cysteine residues. Furthermore, analysis of MnP activity showed that metal ions (Mn²⁺ and Cu²⁺) and static liquid culture significantly influenced MnP activity. A maximum MnP activity (>14.0 U/mL) toward 2,6-DMP was observed in static liquid culture after the addition of Mn²⁺ (1 mM) or Cu²⁺ (0.2 or 2 mM). Moreover, qPCR analysis showed that Mn²⁺ obviously upregulated the Group I MnP subfamily (T_trogii_09901, 09904, 09903, and 09906), while Cu²⁺ and H₂O₂, along with changing temperatures, mainly induced the Group II MnP subfamily (T_trogii_11984, 11971, 11985, and 11983), suggesting diverse functions of fungal MnPs in growth and development, stress response, etc. Our studies here systematically analyzed the gene structure, expression, and regulation of the TtMnP gene family in T. trogii, one of the important lignocellulose-degrading fungi, and these results extended our understanding of the diversity of the MnP gene family and helped to improve MnP production and appilications of Trametes strains and other white-rot fungi.

An Engineered Thermostable Laccase with Great Ability to Decolorize and Detoxify Malachite Green

Laccases can catalyze the remediation of hazardous synthetic dyes in an eco-friendly manner, and thermostable laccases are advantageous to treat high-temperature dyeing wastewater. A novel laccase from Geothermobacter hydrogeniphilus (Ghlac) was cloned and expressed in Escherichia coli. Ghlac containing 263 residues was characterized as a functional laccase of the DUF152 family. By structural and biochemical analyses, the conserved residues H78, C119, and H136 were identified to bind with one copper atom to fulfill the laccase activity. In order to make it more suitable for industrial use, Ghlac variant Mut2 with enhanced thermostability was designed. The half-lives of Mut2 at 50 °C and 60 °C were 80.6 h and 9.8 h, respectively. Mut2 was stable at pH values ranging from 4.0 to 8.0 and showed a high tolerance for organic solvents such as ethanol, acetone, and dimethyl sulfoxide. In addition, Mut2 decolorized approximately 100% of 100 mg/L of malachite green dye in 3 h at 70 °C. Furthermore, Mut2 eliminated the toxicity of malachite green to bacteria and Zea mays. In summary, the thermostable laccase Ghlac Mut2 could effectively decolorize and detoxify malachite green at high temperatures, showing great potential to remediate the dyeing wastewater.

Enzyme-assisted bioremediation approach for synthetic dyes and polycyclic aromatic hydrocarbons degradation

Environmental protection from emerging pollutants has become a significant challenge for mankind as an increasing number of contaminants, including synthetic dyes and polycyclic aromatic hydrocarbons (PAHs), represent a serious risk to ecological and environmental balance. Most synthetic dyes have complex aromatic structures and are resistant to degrade by classical approaches, such as physical and chemical processes, including adsorption, chemical coagulation, flocculation, ion exchange, membrane separation, froth flotation, and reverse osmosis. Enzymes-assisted catalytic transformation of pollutants has become a potential alternative to classical methods because of their ability to react with complex compounds, a quick degradation rate, and producing less harmful by-products. Plant peroxidases, and microbial laccase and lignin-degrading peroxidases (manganese and lignin peroxidase) have gained significant attention for treating aromatic waste due to their capability of oxidizing and detoxifying a wide range of recalcitrant xenobiotics, including PAHs and synthetic dyes. Peroxidases being efficient biocatalysts detoxify an array of toxic compounds by simple free-radical mechanism resulting in the formation of oxidized and depolymerized products of significantly reduced toxicity. Moreover, it is an ecofriendly and economically favorable approach towards the biodegradation of recalcitrant and toxic industrial waste. Among microbial and plant peroxidases, bacterial enzymes have broad substrate specificity and can transform a wide range of recalcitrant substrates. Ligninolytic enzymes oxidize the aromatic ring into quinones and acids by producing free hydroxyl radicals instead of dihydrodiols and mineralize aromatic hydrocarbon in combination with cytochrome P450, monooxygenases, and epoxide hydrolases. In the review, an attempt has been made to provide detailed knowledge about the availability of inexpensive peroxidases sources, their mechanism of action, and degradation potential. The present review summarizes the exploitation of peroxidases from plants, bacteria, and fungus (manganese peroxidase, lignin peroxidase, and laccases) for detoxification and degradation of textile dyes as well as PAHs. Conclusively, peroxidases have great potential to react with almost all classes of synthetic dyes and most PAHs due to broad substrate specificity and transformed them into less harmful metabolites.

Oxidative Synthesis of Acid Blue 7 Dye Catalyzed by CuO/Silicotungstic Acid in Water-Phase

A catalytic oxidation reaction for Acid Blue 7 dye synthesis was evaluated in water. Without lead oxide or manganese oxide derivatives as oxidants, polyoxometalate catalysts were investigated to reduce the usage of harmful heavy metal. A catalyst was prepared by mixing silicotungstic acid with copper oxide, and aqueous hydrogen peroxide (30%) was used as an oxidizing agent. This reaction proceeded to produce Acid Blue 7 from the corresponding leuco acid after 45 min at 95 °C and was viable for a 10 g-scale synthesis.

Metagenomic Insight of a Full Scale Eco-Friendly Treatment System of Textile Dye Wastewater Using Bioaugmentation of the Composite Culture CES-1

Effects of bioaugmentation of the composite microbial culture CES-1 on a full scale textile dye wastewater treatment process were investigated in terms of water quality, sludge reduction, dynamics of microbial community structures and their functional genes responsible for degradation of azo dye, and other chemicals. The removal efficiencies for Chemical Oxygen Demand (COD), Total Nitrogen (T-N), Total Phosphorus (T-P), Suspended Solids (SS), and color intensity (96.4%, 78.4, 83.1, 84.4, and 92.0, respectively) 300-531 days after the augmentation were generally improved after bioaugmentation. The denitrification linked to T-N removal appeared to contribute to the concomitant COD removal that triggered a reduction of sludge (up to 22%) in the same period of augmentation. Azo dye and aromatic compound degradation and other downstream pathways were highly metabolically interrelated. Augmentation of CES-1 increased microbial diversity in the later stages of augmentation when a strong microbial community selection of Acinetobacterparvus, Acinetobacterjohnsonii, Marinobacter manganoxydans, Verminephrobacter sp., and Arcobacter sp. occurred. Herein, there might be a possibility that the CES-1 augmentation could facilitate the indigenous microbial community successions so that the selected communities made the augmentation successful. The metagenomic analysis turned out to be a reasonable and powerful tool to provide with new insights and useful biomarkers for the complex environmental conditions, such as the full scale dye wastewater treatment system undergoing bioaugmentation.

Effective removal of malachite green dye from aqueous solution in hybrid system utilizing agricultural waste as particle electrodes

A comparison study of an electrolytic, adsorption, and a novel hybrid method towards the removal of malachite green (MGD) dye from the aquatic environment utilizing agricultural biomass, Eucalyptus globulus seeds was examined. The synthesized material has been characterized by thermogravimetric analysis, SEM, FTIR, and XRD. The acid-modified biosorbent developed a microporous structure suggesting a suitable removal process of MDG. The hybrid method was carried in an indigenously designed three-phase three-dimensional electrolytic reactor with varying applied voltage (6, 9, and 12 V) with biosorbent serving as particle electrode. The hybrid method gave the highest removal rate at a voltage of 12 V, compared to other methods. Moreover, the dye removal capacity increased with increased voltage, and contact time was optimized at 15 min. The adsorption isotherm was well fitted with Freundlich isotherm and kinetic data represented pseudo-second-order. Intra particle diffusion studies suggested no interference with gradual adsorption from macropores to micropores. The removal efficiency of particles electrodes for 6, 9, and 12 V were 95, 97, and 99.8%, respectively. The higher removal of MDG towards the hybrid system may be assigned to the synergistic effect of electrolytic and adsorption systems. Regeneration studies indicated that the biosorbent can be reused up to ten times without appreciable loss of efficiency.

Revealing two important tryptophan residues with completely different roles in a dye-decolorizing peroxidase from Irpex lacteus F17

BACKGROUND

Dye-decolorizing peroxidases (DyPs) represent a novel family of heme peroxidases that use H₂O₂ as the final electron acceptor to catalyze the oxidation of various organic compounds. A DyP from Irpex lacteus F17 (Il-DyP4, corresponding to GenBank MG209114), obtained by heterologous expression, exhibits a high catalytic efficiency for phenolic compounds and a strong decolorizing ability toward various synthetic dyes. However, the enzyme structure and the catalytic residues involved in substrate oxidation remain poorly understood.

RESULTS

Here, we obtained a high-resolution structure (2.0 Å, PDB: 7D8M) of Il‑DyP4 with α-helices, anti-parallel β-sheets and one ferric heme cofactor sandwiched between two domains. The crystal structure of Il‑DyP4 revealed two heme access channels leading from the enzyme molecular surface to its heme region, and also showed four conserved amino acid residues forming the pocket for the conversion of hydrogen peroxide into the water molecule. In addition, we found that Trp264 and Trp380, were two important residues with different roles in Il‑DyP4, by using site-directed mutagenesis and an electron paramagnetic resonance (EPR) study. Trp264 is a noncatalytic residue that mainly is used for maintaining the normal spatial conformation of the heme region and the high-spin state of heme Fe³⁺ of Il‑DyP4, while Trp380 serves as the surface-exposed radical-forming residue that is closely related to the oxidation of substrates including not only bulky dyes, but also simple phenols.

CONCLUSIONS

This study is important for better understanding the catalytic properties of fungal DyPs and their structure-function relationships.

Efficient biodegradation of malachite green by an artificial enzyme designed in myoglobin

Synthetic dyes such as malachite green (MG) have a wide range of applications. Meanwhile, they bring great challenges for environmental security and cause potential damages to human health. Compared with traditional approaches, enzymatic catalysis is an emerging technique for wastewater treatment. As alternatives to natural enzymes, artificial enzymes have received much attention for potential applications. In previous studies, we have rationally designed artificial enzymes based on myoglobin (Mb), such as by introducing a distal histidine (F43H mutation) and creating a channel to the heme pocket (H64A mutation). We herein show that the artificial enzyme of F43H/H64A Mb can be successfully applied for efficient biodegradation of MG under weak acid conditions. The degradation efficiency is much higher than those of natural enzymes, such as dye-decolorizing peroxidase and laccase (13-18-fold). The interaction of MG and F43H/H64A Mb was investigated by using both experimental and molecular docking studies, and the biodegradation products of MG were also revealed by UPLC-ESI-MS analysis. Based on these results, we proposed a plausible biodegradation mechanism of MG. With the high-yield of overexpression in E. coli cells, this study suggests that the artificial enzyme has potential applications in the biodegradation of MG in fisheries and textile industries.

Kinetics of nutrients remediation from sugar industry effluent-treated substrate using Agaricus bisporus: mushroom yield and biochemical potentials

This study investigated the yield and biochemical potential of Agaricus bisporus mushroom cultivated on agricultural waste substrate supplemented with treated sugar industry effluent (SIE). Laboratory-scale experiments were performed for the cultivation of A. bisporus on a mixture of wheat straw and sugar cane bagasse moistened with different doses of borewell water (BWW) and treated SIE (0-100%). Besides this, the simultaneous effects of the SIE amendment on total Kjeldahl's nitrogen (TKN) and total phosphorus (TP) contents of substrate and kinetics of their utilization by A. bisporus were studied. Results showed a relatively higher utilization of TKN (38.10 ± 1.60%) and TP (47.4 ± 6.44%) in a 25:75 ratio of BWW and SIE, respectively. The kinetics studies of TKN and TP utilization using Lineweaver-Burk models described the maximum specific utilization rates (V _max) of 0.165 and 0.125 mg·kg^-1·d^-1 and saturation points (K _m ) of 72.401 and 33.283 mg·kg^-1, respectively, which are in good agreement as indicated by R ² values (> 0.90). In addition, the maximum significant (P < 0.01) yield (159.31 ± 8.85 g·Kg^-1), biological efficiency (106.21 ± 3.84%), total phenols (3.03 ± 0.07 mg·g^-1), ascorbic acid (0.44 ± 0.03 mg·g^-1), and β-carotene (3.36 ± 0.05 μg·g^-1) of A. bisporus were observed using the same treatment. Therefore, this paper reported sustainable utilization of TKN and TP nutrients from SIE for A. bisporus mushroom cultivation.

Studies on the characteristics and mechanism of aerobic biodegradation of tetrabromobisphenol A by Irpex lacteus F17

The study investigated the characteristics of aerobic degradation of tetrabromobisphenol A (TBBPA) by Irpex lacteus F17 (I. lacteus F17) under four different cometabolic substrates (phenol, glucose, sodium pyruvate, and sodium citrate). The biodegradation of TBBPA by I. lacteus F17 could be enhanced via cometabolism, and glucose (8 g/L) was confirmed to be the optimum carbon source. For different initial solution pH ranging from 3.0 to 8.0, the results showed that I. lacteus F17 could be applied to biodegrade TBBPA in a wide pH range of 4.0-8.0, and the degradation rate could reach the maximum 75.31%, while the debromination rate reached the maximum 12.40% under pH 5.0. In addition, it has been confirmed that Mn²⁺ (50 μmol/L) could promote the secretion of manganese peroxidase and TBBPA biodegradation efficiency. Seven intermediates were identified by gas chromatography-mass spectrometry analysis, and the possible degradation pathways were proposed, which indicated the biodegradation of TBBPA might be subjected to debromination, β-scission, hydroxylation, deprotonation, and oxidation reactions.

One-step procedure for peroxidase concentration, dye separation, and color removal by aqueous two-phase system

The aim of our study is to develop a one-step procedure to remove and degrade dyes from wastewater using a low-cost and efficient system based on aqueous two-phase system (ATPS), a well-known technique used to concentrate and recover enzymes. We investigated the catalytic proprieties of rice bran peroxidase (RBP) and found that this homemade enzyme can remain bound to its substrate for up to 5 days in controlled environments, without denaturing and while maintaining stable oxidation reduction potential (ORP) and pH. This biomolecule showed affinity for the ATPS technique prepared with polyethylene glycol and salt, which improved the relative activity up to 170%. The red dye separation in ATPS top phase was achieved in 3 min, in the RBP presence, with 100% of efficiency, and color removal of 87% was obtained in 24 h of enzymatic reaction. The process has promise to be scaled up to 10-fold and to reuse the reagents from the bottom phase of the ATPS.

Decolorization and detoxification of triphenylmethane dyes by isolated endophytic fungus, Bjerkandera adusta SWUSI4 under non-nutritive conditions

Biodecolorization by microorganisms is a potential treatment technique because they seem to be environmentally safe. In the present study, the decolorization and detoxification of cotton blue, crystal violet, malachite green and methyl violet by endophytic fungi were investigated. Preliminary screening result indicated that SWUSI4, identified as Bjerkandera adusta, demonstrated the best decolorization for the four TPM dyes within 14 days. Furthermore, optimization result demonstrated the decolorization rate could reach above 90% at 24 h by live cells of isolate SWUSI4 when 4 g biomass was added into 100-mL dyes solution with the concentration 50 mg/L and shaking (150 rpm) conditions. Moreover, decolorization mechanism analysis shows that the decolorization was caused by the isolate SWUSI4 that mainly includes both absorption of biomass and/or degradation of enzymes. Biosorption of dyes was attributed to binding to hydroxyl, amino, phosphoryl alkane, and ester–lipids groups based on Fourier transform infrared (FTIR) analyses. The biodegradation potential of SWUSI4 was further suggested by the change of peaks in the ultraviolet–visible (UV–vis) spectra and detection of manganese peroxidase and lignin peroxidase activities. Finally, the phytotoxicity test confirmed that the toxicity of TPM dyes after treatment with SWUSI4 was significantly lower than that before treatment. These results indicate that an endophytic SWUSI4 could be used as a potential TPM dyes adsorption and degradation agent, thus facilitating the study of the plant–endophyte symbiosis in the bioremediation processes.

Current Development in Decolorization of Synthetic Dyes by Immobilized Laccases

The world today is in a quest for new means of environmental remediation as the methods currently used are not sufficient to halt the damage. Mostly, a global direction is headed toward a shift from traditional chemical-based methods to a more ecofriendly alternative. In this context, biocatalysis is seen as a cost-effective, energy saving, and clean alternative. It is meant to catalyze degradation of recalcitrant chemicals in an easy, rapid, green, and sustainable manner. One already established application of biocatalysis is the removal of dyes from natural water bodies using enzymes, notably oxidoreductases like laccases, due to their wide range of substrate specificity. In order to boost their catalytic activity, various methods of enhancements have been pursued including immobilization of the enzyme on different support materials. Aside from increased catalysis, immobilized laccases have the advantages of higher stability, better durability against harsh environment conditions, longer half-lives, resistance against protease enzymes, and the ability to be recovered for reuse. This review briefly outlines the current methods used for detoxification and decolorization of dye effluents stressing on the importance of laccases as a revolutionary biocatalytic solution to this environmental problem. This work highlights the significance of laccase immobilization and also points out some of the challenges and opportunities of this technology.

Degradation and detoxification of azo dyes with recombinant ligninolytic enzymes from Aspergillus sp. with secretory overexpression in Pichia pastoris

Ligninolytic enzymes, including laccase (Lac), manganese peroxidase (MnP) and lignin peroxidase (LiP), have attracted much attention in the degradation of contaminants. Genes of Lac (1827 bp), MnP (1134 bp) and LiP (1119 bp) were cloned from Aspergillus sp. TS-A, and the recombinant Lac (69 kDa), MnP (45 kDa) and LiP (35 kDa) were secretory expressed in Pichia pastoris GS115, with enzyme activities of 34, 135.12 and 103.13 U l-1, respectively. Dyes of different structures were treated via the recombinant ligninolytic enzymes under the optimal degradation conditions, and the result showed that the decolourization rate of Lac on Congo red (CR) in 5 s was 45.5%. Fourier-transform infrared spectroscopy, gas chromatography-mass spectrometry analysis and toxicity tests further proved that the ligninolytic enzymes could destroy the dyes, both those with one or more azo bonds, and the degradation products were non-toxic. Moreover, the combined ligninolytic enzymes could degrade CR more completely compared with the individual enzyme. Remarkably, besides azo dyes, ligninolytic enzymes could also degrade triphenylmethane and anthracene dyes. This suggests that ligninolytic enzymes from Aspergillus sp. TS-A have the potential for application in the treatment of contaminants.

Extracellular expression of mutant CotA-laccase SF in Escherichia coli and its degradation of malachite green

In this study, mutant CotA-laccase SF was successfully expressed in Escherichia coli by co-expression with phospholipase C. The optimized extracellular expression of CotA-laccase SF was 1257.22 U/L. Extracellularly expressed CotA-laccase SF exhibits enzymatic properties similar to intracellular CotA-laccase SF. CotA-laccase SF could decolorize malachite green (MG) under neutral and alkaline conditions. The K_m and k_cat values of CotA-laccase SF to MG were 39.6 mM and 18.36 s^-1. LC-MS analysis of degradation products showed that MG was finally transformed into 4-aminobenzophenone and 4-aminophenol by CotA-laccase. The toxicity experiment of garlic root tip cell showed that the toxicity of MG metabolites decreased. In summary, CotA-laccase SF had a good application prospect for degrading malachite green.

Construction of a combined enzyme system of graphene oxide and manganese peroxidase for efficient oxidation of aromatic compounds

Manganese peroxidase (MnP) from Irpex lacteus F17 has potential use as a biocatalyst in the field of environmental biotechnology because of its unique properties and ability to decompose harmful aromatic compounds. However, its requirement of harsh acidic reaction conditions and its insufficient catalytic activity restrict its practical applications. Here, we combine graphene oxide (GO) and MnP to construct an efficient enzyme system (GO-MnP) with improved catalytic efficiencies and a wide pH range for the oxidation of aromatic substances and dye decolorization. We found that the Michaelis constant (K_m) of GO-MnP for Mn²⁺ was 2.8 times lower and the catalytic efficiency (k_cat/K_m) of GO-MnP was 4.5 times higher than those of MnP, and that the decolorization of various dyes by GO-MnP was significantly improved over the pH range of 4.5-5.5. A comparison of the midpoint redox potentials also reflects the strong oxidation ability of GO-MnP. Furthermore, we demonstrated that, in the GO-MnP system, the MnP activity is mainly determined by the amounts of epoxy and carboxyl groups in GO, based on an analysis of the functional group changes in GO and reduced GO associated with different reduction degrees as shown by X-ray photoelectron spectroscopy.

Pathway and kinetics of malachite green biodegradation by Pseudomonas veronii

Malachite green is a common environmental pollutant that poses a great threat to non-target organisms, including humans. This study reports the characterization of a bacterial strain, Pseudomonas veronii JW3-6, which was isolated from a malachite green enrichment culture. This strain degraded malachite green efficiently in a wide range of temperature and pH levels. Under optimal degradation conditions (32.4 °C, pH 7.1, and inoculum amount of 2.5 × 10⁷ cfu/mL), P. veronii JW3-6 could degrade 93.5% of 50 mg/L malachite green within seven days. Five intermediate products from the degradation of malachite green were identified: leucomalachite green, 4-(dimethylamino) benzophenone, 4-dimethylaminophenol, benzaldehyde, and hydroquinone. We propose a possible degradation pathway based on these findings. The present study is the first to report the degradation of malachite green by P. veronii and the identification of hydroquinone as a metabolite in the degradation pathway.

Recent development in the application of immobilized oxidative enzymes for bioremediation of hazardous micropollutants - A review

During the past several years, abundant progresses has been made in the development of immobilized oxidative enzymes with focus on finding new support materials, improving the immobilization methods and their applications. Nowadays, immobilized oxidative enzymes are broadly accepted as a green way to face the challenge of high amounts of micropollutants in nature. Among all oxidative enzymes, laccases and horseradish peroxidase were used frequently in recent years as they are general oxidative enzymes with ability to oxidize various types of compounds. Immobilized laccase or horseradish peroxidase are showed better stability, and reusability as well as easy separation from reaction mixture that make them more favorable and economic in compared to free enzymes. However, additional improvements are still essential such as: development of the new materials for immobilization with higher capacity, easy preparation, and cheaper price. Moreover, immobilization methods are still need improving to become more efficient and avoid enzyme wasting during immobilization and enzyme leakage through working cycles.

Biodegradation of triphenylmethane dye crystal violet by Cedecea davisae

The present study focuses on the biodegradation of triphenylmethane dye crystal violet (CV) by Cedecea davisae. The degradation of CV was evaluated via ultraviolet absorbance at 254 nm (UV₂₅₄) and chemical oxygen demand (COD) removal, and the kinetics was used to evaluate the degradation efficiency. Intermediate products were analyzed via UV-vis spectroscopy (UV), Fourier transform infrared spectroscopy (FTIR), and high-performance liquid chromatography (HPLC). Results showed that C. davisae was able to decolorize the CV, and the maximum decolorization ratio reached 97%. COD reduction was observed after decolorization, with average removal rates of >90% after 48 h. Moreover, 50% of UV₂₅₄ can be removed after 14 h. The removal efficiency of CV by C. davisae followed first- and second-order reaction kinetics at temperature ranged from 20 °C to 40 °C and pH 4.0 to 6.0, respectively. By using UV, the peak representing the CV disappeared 14 h after CV decolorization, and the degradation of aromatic and naphthalene rings was attributed to the formation of a new metabolite. The FTIR spectra of metabolites showed that a new functional group of OH, CH, CH₂, CH₃, NH, CN, CN, or CO was produced. The chromatograms of HPLC recorded at 589 nm at retention time decreased and were not detected following incubation for 8 h by C. davisae.

Linking Enzymatic Oxidative Degradation of Lignin to Organics Detoxification

The major enzymes involved in lignin degradation are laccase, class II peroxidases (lignin peroxidase, manganese peroxidase, and versatile peroxidase) and dye peroxidase, which use an oxidative or peroxidative mechanism to deconstruct the complex and recalcitrant lignin. Laccase and manganese peroxidase directly oxidize phenolic lignin components, while lignin peroxidase and versatile peroxidase can act on the more recalcitrant non-phenolic lignin compounds. Mediators or co-oxidants not only increase the catalytic ability of these enzymes, but also largely expand their substrate scope to those with higher redox potential or more complicated structures. Neither laccase nor the peroxidases are stringently selective of substrates. The promiscuous nature in substrate preference can be employed in detoxification of a range of organics.

Metagenomics-Based Discovery of Malachite Green-Degradation Gene Families and Enzymes From Mangrove Sediment

Malachite green (MG) is an organic contaminant and the effluents with MG negatively influence the health and balance of the coastal and marine ecosystem. The diverse and abundant microbial communities inhabiting in mangroves participate actively in various ecological processes. Metagenomic sequencing from mangrove sediments was applied to excavate the resources MG-degradation genes (MDGs) and to assess the potential of their corresponding enzymes. A data set of 10 GB was assembled into 33,756 contigs and 44,743 ORFs were predicted. In the data set, 666 bacterial genera and 13 pollutant degradation pathways were found. Proteobacteria and Actinobacteria were the most dominate phyla in taxonomic assignment. A total of 44 putative MDGs were revealed and possibly derived from 30 bacterial genera, most of which belonged to the phyla of Proteobacteria and Bacteroidetes. The MDGs belonged to three gene families, including peroxidase genes (up to 93.54% of total MDGs), laccase (3.40%), and p450 (3.06%). Of the three gene families, three representatives (Mgv-rLACC, Mgv-rPOD, and Mgv-rCYP) which had lower similarities to the closest sequences in GenBank were prokaryotic expressed and their enzymes were characterized. Three recombinant proteins showed different MG-degrading activities. Mgv-rPOD had the strongest activity which decolorized 97.3% of MG (300 mg/L) within 40 min. In addition, Mgv-rPOD showed a more complete process of MG degradation compared with other two recombinant proteins according to the intermediates detected by LC-MS. Furthermore, the high MG-degrading activity was maintained at low temperature (20°C), wider pH range, and the existence of metal ions and chelating agent. Mgv-rLACC and Mgv-rCYP also removed 63.7% and 54.1% of MG (20 mg/L) within 24 h, respectively. The results could provide a broad insight into discovering abundant genetic resources and an effective strategy to access the eco-friendly way for preventing coastal pollution.

Comprehensive investigation of a dye-decolorizing peroxidase and a manganese peroxidase from Irpex lacteus F17, a lignin-degrading basidiomycete

Irpex lacteus F17 is well-known for its ability to degrade recalcitrant aromatic pollutants, which mainly results from the action of the manganese peroxidase (MnP) that it is able to produce. Recently, the genome sequencing and annotation of this strain provided comprehensive picture of the ligninolytic peroxidase gene family. In addition to revealing the presence of 13 MnPs, genes for five dye-decolorizing peroxidases (DyPs) were also discovered in the I. lacteus F17 genome, which are unrelated to the fungal class II peroxidases. In the present study, amino acid sequences of five DyPs and 13 MnPs, representing two different families of heme peroxidases, were analyzed. Of these, two enzymes, a DyP (Il-DyP4) and a MnP (Il-MnP6) were expressed respectively in Escherichia coli, and were characterized by comparing their molecular models, substrate specificities, and catalytic features. The results showed that Il-DyP4 possessed a higher catalytic efficiency for some representative substrates, and a stronger decolorizing ability to a wide range of synthetic dyes in acidic conditions. Based on electrochemical measurements, Il-DyP4 was found to have a high redox potential of 27 mV at pH 3.5, which was superior to that of Il-MnP6 (− 75 mV), thereby contributing to its ability to oxidize high redox potential substrates, such as veratryl alcohol and polymeric dye Poly R-478. The results highlighted the potential of Il-DyP4 for use in industrial and environmental applications.

Deciphering lignocellulose deconstruction by the white rot fungus Irpex lacteus based on genomic and transcriptomic analyses

BACKGROUND

Irpex lacteus is one of the most potent white rot fungi for biological pretreatment of lignocellulose for second biofuel production. To elucidate the underlying molecular mechanism involved in lignocellulose deconstruction, genomic and transcriptomic analyses were carried out for I. lacteus CD2 grown in submerged fermentation using ball-milled corn stover as the carbon source.

RESULTS

Irpex lacteus CD2 efficiently decomposed 74.9% lignin, 86.3% cellulose, and 83.5% hemicellulose in corn stover within 9 days. Manganese peroxidases were rapidly induced, followed by accumulation of cellulase and hemicellulase. Genomic analysis revealed that I. lacteus CD2 possessed a complete set of lignocellulose-degrading enzyme system composed mainly of class II peroxidases, dye-decolorizing peroxidases, auxiliary enzymes, and 182 glycoside hydrolases. Comparative transcriptomic analysis substantiated the notion of a selection mode of degradation. These analyses also suggested that free radicals, derived either from MnP-organic acid interplay or from Fenton reaction involving Fe²⁺ and H₂O₂, could play an important role in lignocellulose degradation.

CONCLUSIONS

The selective strategy employed by I. lacteus CD2, in combination with low extracellular glycosidases cleaving plant cell wall polysaccharides into fermentable sugars, may account for high pretreatment efficiency of I. lacteus. Our study also hints the importance of free radicals for future designing of novel, robust lignocellulose-degrading enzyme cocktails.

Characterization of ligninolytic enzyme production in white-rot wild fungal strains suitable for kraft pulp bleaching

Fungal strains identified by phylogenetic analysis of the ITS rDNA region as Trametes versicolor (CMU-TA01), Irpex lacteus (CMU-84/13), and Phlebiopsis sp. (CMU-47/13) are able to grow on and bleach kraft pulp (KP) in a simple solid-state fermentation (SSF) assay conducted in Petri dishes. Kappa number reductions obtained with Phlebiopsis sp. (48.3%), T. versicolor (43%), and I. lacteus (39.3%), evidence their capability for lignin breakdown. Scanning electron microscopy images of KP fibers from SSF assays demonstrated increased roughness and striation, evidencing significant cell wall modification. T. versicolor produces laccase (Lac), manganese peroxidase (MnP), and lignin peroxidase (LiP) in potato dextrose broth (PDB), PDB + CuSO₄, and PDB + KP, whereas Phlebiopsis sp. and I. lacteus showed no Lac and low LiP activities in all media. Compared to PDB, the highest increase in Lac (7.25-fold) and MnP (2.37-fold) activities in PDB + CuSO₄ occur in T. versicolor; for LiP, the greatest changes (6.95-fold) were observed in I. lacteus. Incubation in PDB + KP shows significant increases in Lac and MnP for T. versicolor, MnP and LiP for Phlebiopsis sp., and none for I. lacteus. SSF assays in Petri plates are a valuable tool to select fungi that are able to delignify KP. Here, delignification by Phlebiopsis sp. of this substrate is reported for the first time, and MnP activity was strongly associated with the delignification ability of the studied strains. The obtained results suggest that the studied fungal strains have biotechnological potential for use in the paper industry.

Genome sequence of the white-rot fungus Irpex lacteus F17, a type strain of lignin degrader fungus

Irpex lacteus, a cosmopolitan white-rot fungus, degrades lignin and lignin-derived aromatic compounds. In this study, we report the high-quality draft genome sequence of I. lacteus F17, isolated from a decaying hardwood tree in the vicinity of Hefei, China. The genome is 44,362,654 bp, with a GC content of 49.64% and a total of 10,391 predicted protein-coding genes. In addition, a total of 18 snRNA, 842 tRNA, 15 rRNA operons and 11,710 repetitive sequences were also identified. The genomic data provides insights into the mechanisms of the efficient lignin decomposition of this strain.

Decolorization pathways of anthraquinone dye Disperse Blue 2BLN by Aspergillus sp. XJ-2 CGMCC12963

Anthraquinone dye represents an important group of recalcitrant pollutants in dye wastewater. Aspergillus sp XJ-2 CGMCC12963 showed broad-spectrum decolorization ability, which could efficiently decolorize and degrade various anthraquinone dyes (50 mg L^-1) under microaerophilic condition. And the decolorization rate of 93.3% was achieved at 120 h with Disperse Blue 2BLN (the target dye). Intermediates of degradation were detected by FTIR and GC-MS, which revealed the cleavage of anthraquinone chromophoric group and partial mineralization of target dye. In addition, extracellular manganese peroxidase showed the most closely related to the increasing of decolorization rate and biomass among intracellular and extracellular ligninolytic enzymes. Given these results, 2 possible degraded pathways of target dye by Aspergillus sp XJ-2 CGMCC12963 were proposed first in this work. The degradation of Disperse Blue 2BLN and broad spectrum decolorization ability provided the potential for Aspergillus sp XJ-2 CGMCC12963 in the treatment of wastewater containing anthraquinone dyes.

Degradation of disperse blue 2BLN by oleaginous C. sorokiniana XJK

In this study, an oil-producing freshwater microalgae Chlorella sorokiniana XJK was identified and used for the degradation of disperse blue 2BLN.