Enzymatic degradation and detoxification of azo dye Congo red by a new laccase from Oudemansiella canarii

Homologous amino acids promoted co-immobilization of laccase and mediator onto geopolymer microspheres for enhancing degradation of dyes in water

A new strategy for co-immobilization of laccase (Lac) and mediator 2,2'-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) on geopolymer microspheres (GM) was reported in this work, which was promoted by pre-embedded homologous amino acids, i.e., histidine (His) and cysteine (Cys). The GM-H₂C₁ produced with a His/Cys ratio of 2:1 was highly efficient in co-immobilizing Lac and ABTS. The as-prepared composite biocatalyst (Lac-ABTS@GM-H₂C₁) exhibited the highest degradation rate (94.78%) to the model pollutant (Congo Red, CR), which was superior to free Lac-ABTS (79.23%) and Lac@GM-H₂C₁ (53.82%). The enhanced degradation efficiency of CR by the Lac-ABTS@GM-H₂C₁ was due to the promoted electron transfer and shortened mass transfer distance. Moreover, Lac-ABTS@GM-H₂C₁ demonstrated good pH resistance, competitive storage stability, and good reusability during ten cycles of CR degradation.

Production of fungal laccase on pineapple waste and application in detoxification of malachite green

The main purpose of this work was to use pineapple crowns as substrate for optimizing laccase production by Trametes versicolor in lab-scale experiments. One-factor-at-the-time analysis and response surface methodology were used to optimize production. A single laccase with molecular weight of 45 kDa was the main protein produced. A maximal laccase activity of 60.73 ± 1.01 U/g was obtained in 7-day cultures, representing a 6.7-fold increase compared to non-optimized conditions. The optimized conditions were temperature: 28 °C; initial moisture: 90%; glucose: 8.38%; yeast extract: 2.86%. Combining activity and stability, the best conditions for using this laccase during the long periods required by large-scale processes are pH 4.0-5.0 and temperature of 40-50 °C. Under these conditions, the crude laccase was efficient in detoxifying the dye malachite green with a K_M of 14.33 ± 1.94 µM and a V_max of 0.482 ± 0.029 µM/min with 0.1 units/mL. It can be concluded that pineapple crown leaves can be effectively used as substrate by T. versicolor for producing laccase under solid-state culture conditions. Laccase is an industrially relevant enzyme and its production with concomitant valorization of pineapple crowns as substrate offers highly interesting perspectives.

The production of laccases by white-rot fungi under solid-state fermentation conditions

Laccases (E.C. 1.10.3.2) produced by white-rot fungi (WRF) can be widely used, but the high cost prevents their use in large-scale industrial processes. Finding a solution to the problem could involve laccase production by solid-state fermentation (SSF) simulating the natural growth conditions for WRF. SSF offers several advantages over conventional submerged fermentation (SmF), such as higher efficiency and productivity of the process and pollution reduction. The aim of this review is therefore to provide an overview of the current state of knowledge about the laccase production by WRF under SSF conditions. The focus is on variations in the up-stream process, fermentation and down-stream process and their impact on laccase activity. The variations of up-stream processing involve inoculum preparation, inoculation of the medium and formulation of the propagation and production media. According to the studies, the production process can be shortened to 5-7 days by the selection of a suitable combination of lignocellulosic material and laccase producer without the need for any additional components of the culture medium. Efficient laccase production was achieved by valorisation of wastes as agro-food, municipal wastes or waste generated from wood processing industries. This leads to a reduction of costs and an increase in competitiveness compared to other commonly used methods and/or procedures. There will be significant challenges and opportunities in the future, where SSF could become more efficient and bring the enzyme production to a higher level, especially in new biorefineries, bioreactors and biomolecular/genetic engineering.

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.

Microbial valorization of lignin: Prospects and challenges

Lignin is the world's second most prevalent biomaterial, but its effective value-added product valorization methods are still being developed. The most common preparation processes for converting lignin to platform chemicals and biofuels are fragmentation and depolymerization. Due to its structural diversity, fragmentation generally produces a variety of products, necessitating tedious separation and purifying methods to isolate the desired products. Bacterial-based techniques are commonly utilized for lignin fragmentation due to their high metabolitic activity. Recent advancements in lignin valorization utilizing bacteria, such as lignin decomposing microbes and major pathways involved that can breakdown lignin into various valuable products namely lipids, furfural, vanillin, polyhydroxybutyrate, poly lactic acid blends were discussed in this review. This review also covers the genetic and fermentation methodologies to enhance lignin decomposition, challenges and future trends of microbe based lignin valorization.

Free and immobilized biocatalysts for removing micropollutants from water and wastewater: Recent progress and challenges

Enzymatic conversion of micropollutants into less-toxic derivatives is an important bioremediation strategy. This paper aims to critically review the progress in water and wastewater treatment by both free and immobilized enzymes presenting this approach as highly efficient and performed under environmentally benign and friendly conditions. The review also summarises the effects of inorganic and organic wastewater matrix constituents on enzymatic activity and degradation efficiency of micropollutants. Finally, application of enzymatic reactors facilitate continuous treatment of wastewater and obtaining of pure final effluents. Of a particular note, enzymatic treatment of micropollutants from wastewater has been mostly reported by laboratory scale studies. Thus, this review also highlights key research gaps of the existing techniques and provides future perspectives to facilitate the transfer of the lab-scale solutions to a larger scale and to improve operationability of biodegradation processes.

Chemically induced oxidative stress improved bacterial laccase-mediated degradation and detoxification of the synthetic dyes

To alleviate the risk of textile effluent, the development of highly effective bioremediation strategies for synthetic dye removal is needed. Herein, we aimed to assess whether intensified bioactivity of Bacillus pumilus ZB1 by oxidative stress could improve the removal of textile dyes. Methyl methanesulfonate (MMS) induced oxidative stress significantly promoted laccase expression of B. pumilus ZB1. Both the level of hydrogen dioxide and superoxide anion showed a significant positive correlation with laccase activity (RSQ = 0.963 and 0.916, respectively) along with the change of MMS concentration. The regulation of laccase expression was closely related to oxidative stress. The overexpressed laccase in the supernatant improved the decolorization of synthetic dyes (16.43% for Congo Red, 54.05% for Crystal Violet, and 41.61% for Reactive Blue 4). Laccase was subsequently expressed in E. coli. Investigation of the potential of bacterial laccase in dye remediation using Congo Red showed that an effective degradation of azo dye could be achieved with laccase treatment. Laccase remediation alleviated the cytotoxicity of Congo Red to human hepatocytes. In silico study identified eight amino acid residues of laccase involved in binding with Congo Red. Overall, regulation of oxidative stress towards bacterium can be used as a promising approach for the improvement of bacterial bioactivity in synthetic dye remediation.

Transformation of Reactive Blue 19 by a recombinant peroxidase DyP

Wastewater containing recalcitrant dyes causes environmental problems. A new superfamily of heme-containing peroxidases, dye-decolorizing peroxidases (DyPs), has been found to decolorize different kinds of dyes, especial anthraquinone dyes efficiently. However, the mechanism of dyes degradation by DyPs has not been fully understood and the toxicity of dye degradation intermediates by DyPs catalysis to microbes is unclear. In this study, a purified recombinant Thermobifida fusca DyP (TfuDyP) in E. coli BL21(DE3) was used to treat Reactive Blue 19 (RB19), an anthraquinone dye. The reaction intermediates analyzed by ultra performance liquid chromatography/mass spectroscopy (UPLC-MS) indicated the initial site of TfuDyP attack on RB19. In addition, it was found that both RB19 and its incomplete degradation products inhibited the growth of Bacillus subtilis. These findings provided a novel understanding of DyPs catalysis to anthraquinone dyes.

Decolourisation of textile dye by laccase: Process evaluation and assessment of its degradation bioproducts

Biodegradation of environmentally hazardous synthetic dyes by enzymes has been achieved the highest interest in recent years. In this work, we optimized Remazol Brilliant Blue R (RBBR) dye biodegradation by Arthrographis kalrae derived laccase via the Box-Behnken design (BBD) approach of the surface response methodology (RSM). Optimization of dye decolourisation by one variable at a time (OVAT) approach resulted in optimal dye decolourisation at laccase dose (2 IU mL^-1), pH (7.0), temperature (35 °C), incubation time (240 min), and initial dye concentration (100 mg L^-1). The optimized process through BBD enhanced dye decolourisation (97.18%). Fourier Transform Infrared Spectroscopy and UV-Visible Spectrophotometry have proven biodegradation. In addition, in comparison to untreated samples, the laccase-treated dye sample showed relatively less phyto- and cytotoxic effect on Allium cepa L. Extra Precision Glide docking exhibited the binding affinity score of -5.355 kcal mol^-1, between laccase-RBBR complex.

Biotechnological potential of fungi from a mangrove ecosystem: Enzymes, salt tolerance and decolorization of a real textile effluent

The mangrove is an ecosystem bounded by the line of the largest tide in size that occurs in climatic and subtropical regions. In this environment, microorganisms and their enzymes are involved in a series of transformations and nutrient cycling. To evaluate the biotechnological potential of fungi from a mangrove ecosystem, samples from mangrove trees were collected at the Paranaguá Estuarine Complex in Brazil and 40 fungal isolates were obtained, cultivated, and screened for hydrolytic and ligninolytic enzymes production, adaptation to salinity and genetic diversity. The results showed a predominance of hydrolytic enzymes and fungal tolerance to ≤ 50 g L^-1 sodium chloride (NaCl) concentration, a sign of adaptive halophilia. Through morphological and molecular analyses, the isolates were identified as: Trichoderma atroveride, Microsphaeropsis arundinis, Epicoccum sp., Trichoderma sp., Gliocladium sp., Geotrichum sp. and Cryphonectria sp. The ligninolytic enzymatic potential of the fungi was evaluated in liquid cultures in the presence and absence of seawater and the highest activity of laccase among isolates was observed in the presence of seawater with M. arundinis (LB07), which produced 1,037 U L^-1. Enzymatic extracts of M. arundinis fixed at 100 U L^-1 of laccase partially decolorized a real textile effluent in a reaction without pH adjustment and chemical mediators. Considering that mangrove fungi are still few explored, the results bring an important contribution to the knowledge about these microorganisms, as their ability to adapt to saline conditions, biodegradation of pollutants, and enzymatic potential, which make them promising candidates in biotechnological processes.

Acid-based lignocellulosic biomass biorefinery for bioenergy production: Advantages, application constraints, and perspectives

The production of chemicals and fuels from renewable biomass with the primary aim of reducing carbon footprints has recently become one of the central points of interest. The use of lignocellulosic biomass for energy production is believed to meet the main criteria of maximizing the available global energy source and minimizing pollutant emissions. However, before usage in bioenergy production, lignocellulosic biomass needs to undergo several processes, among which biomass pretreatment plays an important role in the yield, productivity, and quality of the products. Acid-based pretreatment, one of the existing methods applied for lignocellulosic biomass pretreatment, has several advantages, such as short operating time and high efficiency. A thorough analysis of the characteristics of acid-based biomass pretreatment is presented in this review. The environmental concerns and future challenges involved in using acid pretreatment methods are discussed in detail to achieve clean and sustainable bioenergy production. The application of acid to biomass pretreatment is considered an effective process for biorefineries that aim to optimize the production of desired products while minimizing the by-products.

A review on catalytic-enzyme degradation of toxic environmental pollutants: Microbial enzymes

Industrialization and other human anthropogenic activities cause serious threats to the environment. The toxic pollutants can cause detrimental diseases on diverse living beings in their respective ecosystems. Bioremediation is one of the efficient remediation methods in which the toxic pollutants are removed from the environment by the application of microorganisms or their biologically active products (enzymes). Typically, the microorganisms in the environment produce various enzymes to immobilize and degrade the toxic environmental pollutants by utilizing them as a substrate for their growth and development. Both the bacterial and fungal enzymes can degrade the toxic pollutants present in the environment and convert them into non-toxic forms through their catalytic reaction mechanism. Hydrolases, oxidoreductases, dehalogenases, oxygenases and transferases are the major classes of microbial enzymes responsible for the degradation of most of the toxic pollutants in the environment. Recently, there are different immobilizations and genetic engineering techniques have been developed to enhance enzyme efficiency and diminish the process cost for pollutant removal. This review focused on enzymatic removal of toxic pollutants such as heavy metals, dyes, plastics and pesticides in the environment. Current trends and further expansion for efficient removal of toxic pollutants through enzymatic degradation are also reviewed in detail.

Efficient removal of various textile dyes from wastewater by novel thermo-halotolerant laccase

A novel thermostable/halotolerant metagenome-derived laccase (PersiLac2) from tannery wastewater was purified to remove textile dyes in this study. The enzyme was highly active over a wide temperature and pH range and maintained 73.35% of its initial activity after 30 days, at 50 °C. The effect of various metal and organic-solvent tolerance on PersiLac2 showed, retaining greater than 53% activity at 800 mM of metal ions, 52.12% activity at 6 M NaCl, and greater than 44.09% activity at 20% organic solvents. PersiLac2 manifested effective removal of eight different textile dyes from azo, anthraquinone, and triphenylmethane families. It decolorized 500 mg/L of Alizarin yellow, Carmine, Congo red and Bromothymol blue with 99.74-55.85% efficiency after 15 min, at 50 °C, without mediator. This enzyme could practically remove dyes from a real textile effluent and it displayed significant detoxification in rice seed germination tests. In conclusion, PersiLac2 could be useful in future for decolorization/detoxification of wastewater.

Introducing a Thermo-Alkali-Stable, Metallic Ion-Tolerant Laccase Purified From White Rot Fungus Trametes hirsuta

This study introduces a valuable laccase, designated ThLacc-S, purified from white rot fungus Trametes hirsuta. ThLacc-S is a monomeric protein in nature with a molecular weight of 57.0 kDa and can efficiently metabolize endocrine disrupting chemicals. The enzyme was successfully purified to homogeneity via three consecutive steps consisting of salt precipitation and column chromatography, resulting in a 20.76-fold increase in purity and 46.79% yield, with specific activity of 22.111 U/mg protein. ThLacc-S was deciphered as a novel member of the laccase family and is a rare metalloenzyme that contains cysteine, serine, histidine, and tyrosine residues in its catalytic site, and follows Michaelis-Menten kinetic behavior with a K _m and a k _cat /K _m of 87.466 μM and 1.479 s^-1μM^-1, respectively. ThLacc-S exerted excellent thermo-alkali stability, since it was markedly active after a 2-h incubation at temperatures ranging from 20 to 70°C and retained more than 50% of its activity after incubation for 72 h in a broad pH range of 5.0-10.0. Enzymatic activities of ThLacc-S were enhanced and preserved when exposed to metallic ions, surfactants, and organic solvents, rendering this novel enzyme of interest as a green catalyst for versatile biotechnological and industrial applications that require these singularities of laccases, particularly biodegradation and bioremediation of environmental pollutants.

Exploration of Microbial Factories for Synthesis of Nanoparticles - A Sustainable Approach for Bioremediation of Environmental Contaminants

The nanomaterials synthesis is an intensifying research field due to their wide applications. The high surface-to-volume ratio of nanoparticles and quick interaction capacity with different particles make them as an attractive tool in different areas. Conventional physical and chemical procedures for development of metal nanoparticles become outmoded due to extensive production method, energy expenditure and generation of toxic by-products which causes significant risks to the human health and environment. Hence, there is a growing requirement to search substitute, non-expensive, reliable, biocompatible and environmental friendly methods for development of nanoparticles. The nanoparticles synthesis by microorganisms has gained significant interest due to their potential to synthesize nanoparticles in various sizes, shape and composition with different physico-chemical properties. Microbes can be widely applied for nanoparticles production due to easy handling and processing, requirement of low-cost medium such as agro-wastes, simple scaling up, economic viability with the ability of adsorbing and reducing metal ions into nanoparticles through metabolic processes. Biogenic synthesis of nanoparticles offers clean, non-toxic, environmentally benign and sustainable approach in which renewable materials can be used for metal reduction and nanoparticle stabilization. Nanomaterials synthesized through microbes can be used as a pollution abatement tool as they also contain multiple functional groups that can easily target pollutants for efficient bioremediation and promotes environmental cleanup. The objective of the present review is to highlight the significance of micro-organisms like bacteria, actinomycetes, filamentous fungi, yeast, algae and viruses for nanoparticles synthesis and advantages of microbial approaches for elimination of heavy metals, dyes and wastewater treatment.

Degradation and Detoxification of Congo Red azo dye by Immobilized Laccase of Streptomyces sviceus

The discharge of textile effluents enriched with reactive azo dyes is of critical importance owing to inability of the dyes to degrade in waste water and their carcinogenic, mutagenic effects to various organisms. This study initiated based on the need to gaze into molecular mechanism of marine bacterial bioremediation process to develop strategies for the decolorization and detoxification of the synthetic azo dyes. The experimental work carried out to explore decolorization and degradation efficacy of laccase derived from marine actinobacteria, Streptomyces sviceus by choosing Congo red-21 as model azo dye. The extracellular production of laccase was confirmed with plate assay in medium supplemented with ABTS as substrate. Laccase was purified to homogeneity from 72hrs culture of Streptomyces sviceus by Fast performance liquid chromatography and the molecular size of laccase was noticed as 60 kDa. The purified laccase was immobilized with an efficiency of 82% by Calcium alginate method. The crude, purified and immobilized forms of the laccase enzyme was used to decolorize the Congo red-21. Crude laccase enzyme showed 69% of decolorization of Congo red-21 after 48h where as purified and immobilized laccase represented 78% and 92% of colour removal after 24 h respectively. Fourier-transform infrared spectroscopy, High Performance Liquid Chromatography and Gas chromatography–mass spectrometry were used to unravel the molecular mechanism of dye detoxification and also identify nontoxic products released from Congo Red-21 upon administration with immobilized laccase. Based on GC-MS data, it may deduce that immobilized laccase of Streptomyces sviceus cleaves the Congo red-21 dye followed by oxidative cleavage, desulfonation, deamination, demethylation process.

Laccase as an efficacious approach to remove anticancer drugs: A study of doxorubicin degradation, kinetic parameters, and toxicity assessment

The degradation of an anticancer drug by laccase was investigated for the first time, bringing a new approach to treat these hazardous substances through the direct enzymatic application. Degradations of doxorubicin by laccase were performed in different enzymatic concentrations, pH values and temperatures through kinetic studies. The highest enzymatic degradation of doxorubicin was achieved at pH 7 and 30 ºC, which resembles effluent characteristics from wastewater treatment plants. Assays were carried out in different doxorubicin concentrations to comprehend the enzymatic kinetics of degradation. Michaelis-Menten kinetic parameters obtained were maximum velocity obtained (V_max) of 702.8 µg_DOX h^-1 L^-1 and Michaelis-Menten constant (K_M) of 4.05 µM, which showed a good affinity for the substrate. The toxicity was evaluated against L-929 cell line, and the degraded doxorubicin solution did not show a reduction in cell viability in the concentration of 250 µg L^-1. In contrast, the doxorubicin shows a reduction of 27% in cell viability. Furthermore, in the highest tested concentration (1000 µg L^-1), enzymatic degradation reduced in up 41.4% the toxicity of doxorubicin, which indicates laccase degrades doxorubicin to non-toxic compounds. In conclusion, this study provides a new application to laccase since the results showed great potential to remove anticancer drugs from effluents.

A laccase Gl-LAC-4 purified from white-rot fungus Ganoderma lucidum had a strong ability to degrade and detoxify the alkylphenol pollutants 4-n-octylphenol and 2-phenylphenol

In this study, the ability of laccase Gl-LAC-4, purified from Ganoderma lucidum, to degrade and detoxify two representative alkylphenol pollutants, 4-n-octylphenol and 2-phenylphenol, was systematically studied. Gl-LAC-4 laccase had a very strong ability to degrade high concentrations of 4-n-octylphenol, 2-phenylphenol, and alkylphenol mixtures. The degradation speed of Gl-LAC-4 toward 2-phenylphenol was very fast. Gl-LAC-4 displayed strong tolerance for a variety of metal salts and organic solvents in the degradation of alkylphenols. Gl-LAC-4 showed strong tolerance for high concentrations of various metal salts, such as MgSO₄, MnSO₄, Na₂SO₄, CuSO₄, ZnSO₄, CdSO₄, and K₂SO₄, in the degradation of 4-n-octylphenol and 2-phenylphenol.In the case of the same metal cation, the inhibitory effect of the metal salt with Cl^- as the anion on the degradation of 4-n-octylphenol and 2-phenylphenol by laccase was stronger than that of the metal salt with SO₄^2- as the anion. An increase in the number of chloride ions caused a greater inhibitory effect on alkylphenol degradation by laccase. Gl-LAC-4 exhibited strong tolerance for glycerol, ethylene glycol, butanediol, propylene glycol, and organic solvent mixtures in the degradation of alkylphenols. Gl-LAC-4 treatment significantly reduced or eliminated the phytotoxicity of 4-n-octylphenol and 2-phenylphenol.

Polyethyleneimine-impregnated alkali treated waste bamboo powder for effective dye removal

In this study, the polyethyleneimine (PEI) modified waste bamboo powder (WBP-Na-PEI) was successfully prepared and applied to adsorbing Congo red (CR) dye from aqueous solution. The obtained materials were characterized by field emission scanning electron microscope, X-ray diffraction, Fourier transform-infrared, and thermogravimetric analysis. The results showed that WBP-Na-PEI(1.8 K-5) was synthesized successfully and PEI uniformly covered the WBP-Na-PEI(1.8 K-5) surface. In the process of adsorption, four kinds of influencing factors were discussed, and the adsorption mechanisms such as kinetics, isotherm, thermodynamics were explored. The maximum adsorption capacity of WBP-Na-PEI(1.8 K-5) was 992.94 mg·g^-1 at 298 ± 1 K, and the removal efficiency was over 98%. Pseudo-first-order, pseudo-second-order and intra-particle diffusion models were studied, the results showed that the adsorption process conformed to the pseudo-second-order model, and the rate of this process was controlled by many steps. Furthermore, the removal efficiency of the adsorption kinetics reached 85% within 10 minutes. The results of the isotherm model and thermodynamics showed that the adsorption process was consistent with the Langmuir model and was mainly a spontaneous chemical endothermic process of monolayer. And the removal efficiency of the adsorbent reached 93% at the concentration of 400 mg/L, which can be expected to have a broad prospect in the treatment of CR industrial wastewater.

Characterization of a Novel Laccase LAC-Yang1 from White-Rot Fungus Pleurotus ostreatus Strain Yang1 with a Strong Ability to Degrade and Detoxify Chlorophenols

In this study, a laccase LAC-Yang1 was successfully purified from a white-rot fungus strain Pleurotus ostreatus strain yang1 with high laccase activity. The enzymatic properties of LAC-Yang1 and its ability to degrade and detoxify chlorophenols such as 2,6-dichlorophenol and 2,3,6-trichlorophenol were systematically studied. LAC-Yang1 showed a strong tolerance to extremely acidic conditions and strong stability under strong alkaline conditions (pH 9–12). LAC-Yang1 also exhibited a strong tolerance to different inhibitors (EDTA, SDS), metal ions (Mn²⁺, Cu²⁺, Mg²⁺, Na⁺, K⁺, Zn²⁺, Al³⁺, Co²⁺, and metal ion mixtures), and organic solvents (glycerol, propylene glycol). LAC-Yang1 showed good stability in the presence of Mg²⁺, Mn²⁺, glycerol, and ethylene glycol. Our results reveal the strong degradation ability of this laccase for high concentrations of chlorophenols (especially 2,6-dichlorophenol) and chlorophenol mixtures (2,6-dichlorophenol + 2,3,6-trichlorophenol). LAC-Yang1 displayed a strong tolerance toward a variety of metal ions (Na²⁺, Zn²⁺, Mn²⁺, Mg²⁺, K⁺ and metal ion mixtures) and organic solvents (glycerol, ethylene glycol) in its degradation of 2,6-dichlorophenol and 2,3,6-trichlorophenol. The phytotoxicity of 2,6-dichlorophenol treated by LAC-Yang1 was significantly reduced or eliminated. LAC-Yang1 demonstrated a good detoxification effect on 2,6-dichlorophenol while degrading this compound. In conclusion, LAC-Yang1 purified from Pleurotus ostreatus has great application value and potential in environmental biotechnology, especially the efficient degradation and detoxification of chlorophenols.

Optimization and kinetic modeling of Trametes maxima IIPLC-32 laccase and application in recalcitrant dye decolorization

Enhanced laccase production by the Trametes maxima fungus and its use for decolorization of the textile dye RBBR.

Application of the immobilized enzyme on magnetic graphene oxide nano-carrier as a versatile bi-functional tool for efficient removal of dye from water

Herein, we report bi-functional applications of a novel immobilized enzyme on the modified magnetic graphene oxide (GO) for effective removal of dyes from water. The amine functionalized GO nano-carrier was covalently attached to a model enzyme (PersiManXyn1). The enzyme assays showed that the specific activities of the free and immobilized enzyme were 856.05 and 1141.1 µmolmin^-1mg^-1, respectively. While the free enzyme showed only 5% of its maximum activity, the immobilized PersiManXyn1 preserved more than 35% of its activity, at 90 °C. After four weeks storage, the free enzyme has been deactivated, but the immobilized enzyme retained 54% of its initial activity. The immobilized PersiManXyn1 was proficiently applied for dye removal from water using two strategies. While only pristine nano-carrier and free enzyme showed no considerable catalytic ability, the immobilized PersiManXyn1 could catalytically reduce the concentrated dye solutions within 150 s with superior reusability (94% dye removal after 15^th cycle). Proficient treatment of a real textile effluent by the immobilized PersiManXyn1 approved its practical applications in the water remediation.

Synthetic dyes biodegradation by fungal ligninolytic enzymes: Process optimization, metabolites evaluation and toxicity assessment

This work aimed to provide information that contributes to establishing environmental-friendly methods for synthetic dyes' degradation. The potential decolorization capacity of the crude enzymatic extract produced by Phanerochaete chrysosporium CDBB 686 using corncob as a substrate was evaluated on seven different dyes. Critical variables affecting the in-vitro decolorization process were further evaluated and results were compared with an in-vivo decolorization system. Decolorization with enzymatic extracts presented advantages over the in-vivo system (higher or similar decolorization within a shorter period). Under improved in-vitro process conditions, the dyes with higher decolorization were: Congo red (41.84 %), Poly R-478 (56.86 %), Methyl green (69.79 %). Attempts were made to confirm the transformation of the dyes after the in-vitro process as well as to establish a molecular basis for interpreting changes in toxicity along with the degradation process. In-vitro degradation products of Methyl green presented a toxicity reduction compared with the original dye; however, increased toxicity was found for Congo red degradation products when compared with the original dyes. Thus, for future applications, it is crucial to evaluate the mechanisms of biodegradation of each target synthetic dye as well as the toxicity of the products obtained after enzymatic oxidation.

Studies on laccase mediated conversion of lignin from ginseng residues for the production of sugars

The purpose of this study was to determine the production of sugars from ginseng residues treated with laccase. Laccase was used to degrade lignin from ginseng residues in order to increase the yield of sugars. Reaction conditions, including solid loading, pH, enzyme concentration, incubation temperature, and incubation time, were investigated and optimized. The results showed that the optimum conditions were 20% of solid loading (w/v), pH 7, 300 IU/ml, temperature of 40 °C and incubation time of 6 h. The minimum residual lignin obtained was 59.89%. The results also showed that 56.58% sugars including 12.04% water soluble polysaccharides (WSP), 16.24% water insoluble polysaccharides (WIP) and 5.08% reducing sugar were afforded from delignify substance. Chemical characters of these sugars were analyzed. Pretreat of laccase delignification for sugars production is expected to be applied to other herbal residues.

Fabrication of thermostable and reusable nanobiocatalyst for dye decolourization by immobilization of lignin peroxidase on graphene oxide functionalized MnFe2O4 superparamagnetic nanoparticles

In view of the potential applications of immobilized enzymes, partially purified Lignin Peroxidase (LiP) from Pseudomonas fluorescens LiP-RL5 was immobilized on Graphene Oxide functionalized MnFe2O4 nanoparticles (10 nm, synthesized by sol-gel auto-combustion) to fabricate a new hyperactive and thermostable nanobiocatalyst and thereafter characterized by using standard techniques. Immobilized LiP was quite stable at 50 °C with the half-life of 14 h and showed higher tolerance towards various metal ions and solvents than free LiP. Immobilized LiP retained 50% of enzyme activity even after nine consecutive runs. When tested against various textile dyes, the immobilized LiP was found quite effective with higher dye decolourization efficiency (up to 88%) within 1 h of incubation at 30 °C. The results of this research effort confirmed that the immobilization of LiP and fabrication of nanobiocatalyst increase the efficacy, stability, and reusability of the enzyme which could be efficiently utilized under harsh industrial conditions.

Ligninolytic Enzyme Production and Decolorization Capacity of Synthetic Dyes by Saprotrophic White Rot, Brown Rot, and Litter Decomposing Basidiomycetes

An extensive screening of saprotrophic Basidiomycetes causing white rot (WR), brown rot (BR), or litter decomposition (LD) for the production of laccase and Mn-peroxidase (MnP) and decolorization of the synthetic dyes Orange G and Remazol Brilliant Blue R (RBBR) was performed. The study considered in total 150 strains belonging to 77 species. The aim of this work was to compare the decolorization and ligninolytic capacity among different ecophysiological and taxonomic groups of Basidiomycetes. WR strains decolorized both dyes most efficiently; high decolorization capacity was also found in some LD fungi. The enzyme production was recorded in all three ecophysiology groups, but to a different extent. All WR and LD fungi produced laccase, and the majority of them also produced MnP. The strains belonging to BR lacked decolorization capabilities. None of them produced MnP and the production of laccase was either very low or absent. The most efficient decolorization of both dyes and the highest laccase production was found among the members of the orders Polyporales and Agaricales. The strains with high MnP activity occurred across almost all fungal orders (Polyporales, Agaricales, Hymenochaetales, and Russulales). Synthetic dye decolorization by fungal strains was clearly related to their production of ligninolytic enzymes and both properties were determined by the interaction of their ecophysiology and taxonomy, with a more relevant role of ecophysiology. Our screening revealed 12 strains with high decolorization capacity (9 WR and 3 LD), which could be promising for further biotechnological utilization.

Microbial degradation of dyes: An overview

Industrialization increases use of dyes due to its high demand in paper, cosmetic, textile, leather and food industries. This in turn would increase wastewater generation from dye industrial activities. Various dyes and its structural compounds present in dye industrial wastewater have harmful effects on plants, animals and humans. Synthetic dyes are more resistant than natural dyes to physical and chemical methods for remediation which makes them more difficult to get decolorize. Microbial degradation has been researched and reviewed largely for quicker dye degradation. Genetically engineered microorganisms (GEMs) play important role in achieving complete dye degradation. This paper provides scientific and technical information about dyes & dye intermediates and biodegradation of azo dye. It also compiles information about factors affecting dye(s) biodegradation, role of genetically modified organisms (GMOs) in process of dye(s) degradation and perspectives in this field of research.

Enhancing the decolorization activity of Bacillus pumilus W3 CotA-laccase to Reactive Black 5 by site-saturation mutagenesis

Reactive Black 5 (RB5) is a typical refractory azo dye. Widespread utilization of RB5 has caused a variety of environmental and health problems. The enzymatic degradation of RB5 can be a promising solution due to its superiority as an eco-friendly and cost-competitive process. Bacterial CotA-laccase shows great application prospect to eliminate hazardous dyes from wastewater. However, efficient decolorization of RB5 CotA-laccase generally requires the participation of costly, toxic mediators. In the present study, we modified the amino acids Thr415 and Thr418 near the type 1 copper site and the amino acid Gln442 at the entrance of the substrate-binding pocket of Bacillus pumilus W3 CotA-laccase to boost its RB5 decolorization activity based on molecular docking analysis and site-saturation mutagenesis. Through the strategies, two double site mutants T415D/Q442A and T418K/Q442A obtained demonstrated 43.94 and 52.64% RB5 decolorization rates in the absence of a mediator at pH 10.0, respectively, which were about 3.70- and 4.43-fold higher compared with the wild-type CotA-laccase. Unexpectedly, the catalytic efficiency of the T418K/Q442A to ABTS was enhanced by 5.33-fold compared with the wild-type CotA-laccase. The mechanisms of conferring enhanced activity to the mutants were proposed by structural analysis. In summary, the mutants T415D/Q442A and T418K/Q442A have good application potentials for the biodegradation of RB5. KEY POINTS: • Three amino acids of CotA-laccase were manipulated by site-saturation mutagenesis. • Decolorization rate of two mutants to RB5 was enhanced 3.70- and 4.43-fold, respectively. • The mechanisms of awarding enhanced activity to the mutants were supposed.

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.

Using Electrolytic Manganese Residue to prepare novel nanocomposite catalysts for efficient degradation of Azo Dyes in Fenton-like processes

In this study, Electrolytic Manganese Residue (EMR) was treated by EDTA-2Na/NaOH, ultrasonic etching, and hydrothermal reaction to obtain a novel nanocomposite catalyst (called N-EMR), which then was used, together with H₂O₂, to treat synthetic textile wastewater containing Reactive Red X-3B, Methyl Orange, Methylene blue and Acid Orange 7. Results indicated that the N-EMR had a nano-sheet structure in sizes of 100-200 nm; new iron and manganese oxides with high activity were produced. The mixture of a small amount of N-EMR (40 mg/L) and H₂O₂ (0.4 × 10^-3 M) could removal about 99% of azo dyes (at 100 mg/L in 100 mL) within 6-15 min, much faster than many advanced oxidation processes (AOPs) reported in the literature. The elucidation of the associated mechanism for azo dyes degradation indicates that azo dyes were attacked by superoxide radicals, hydroxyl radicals, and electron holes generated within system. N-EMR was found to be reusable and showed limited inhibition by co-existing anions and cations. Moreover, high removal efficiency of azo dyes could happen in the system with a wide range of pH (1-8.5) and temperatures (25-45 °C), indicating that the process developed in this study may have broad application potential in treatment of azo dyes contaminated wastewater.

Elucidation of fungal dye-decolourizing peroxidase (DyP) and ligninolytic enzyme activities in decolourization and mineralization of azo dyes

AIM

The aim of the study is to investigate the efficiency of Geotrichum candidum in the decolourization and mineralization of synthetic azo dyes.

METHODS AND RESULTS

It includes screening of enzymes from G. candidum and its optimization, followed by decolourization and mineralization studies. Decolourization was observed to be maximum in methyl orange (94·6%) followed by Congo red (85%), trypan blue (70·4%) and Eriochrome Black T (55·6%) in 48 h, suggesting the plausible degradation of the azo dyes by G. candidum. The enzyme activity study showed that DyP-type peroxidase has highest activity of 900 mU ml^-1 compared to that of laccase (405 mU ml^-1 ) and lignin peroxidase (LiP) (324 mU ml^-1 ) at optimized pH (6) and temperature (35°C). Moreover, the rate of decolourization was found to be directly proportional to the production of laccase and LiP, unlike DyP-type peroxidase. Furthermore, mineralization study demonstrated reduction in aromatic amines, showing 20% mineralization of methyl orange.

CONCLUSION

Geotrichum candidum with its enzyme system is able to efficiently decolourize and mineralize the experimental azo dyes.

SIGNIFICANCE AND IMPACT OF THE STUDY

The efficient decolourization and mineralization of azo dyes makes G. candidum a promising alternative in the treatment of textile effluent contaminated with azo dyes.

Fast decolorization of azo dyes in alkaline solutions by a thermostable metal-tolerant bacterial laccase and proposed degradation pathways

Biocatalytic decolorization of azo dyes is hampered by their recalcitrance and the characteristics of textile effluents. Alkaline pH and heavy metals present in colored wastewaters generally limit the activity of enzymes such as laccases of fungal origin; this has led to an increasing interest in bacterial laccases. In this work, the dye decolorization ability of LAC_2.9, a laccase from the thermophilic bacterial strain Thermus sp. 2.9, was investigated. Its resistance towards different pHs and toxic heavy metals frequently present in wastewaters was also characterized. LAC_2.9 was active and highly stable in the pH range of 5.0 to 9.0. Even at 100 mM Cd⁺², As⁺⁵ and Ni⁺² LAC_2.9 retained 99%, 86% and 75% of its activity, respectively. LAC_2.9 was capable of decolorizing 98% of Xylidine, 54% of RBBR, 40% of Gentian Violet, and 33% of Methyl Orange after 24 h incubation at pH 9, at 60 °C, without the addition of redox mediators. At acidic pH, the presence of the mediator 1-hydroxybenzotriazole generally increased the catalytic effectiveness. We analyzed the degradation products of laccase-treated Xylidine and Methyl Orange by capillary electrophoresis and mass spectrometry, and propose a degradation pathway for these dyes. For its ability to decolorize recalcitrant dyes, at pH 9, and its stability under the tested conditions, LAC_2.9 could be effectively used to decolorize azo dyes in alkaline and heavy metal containing effluents.

Laccases: structure, function, and potential application in water bioremediation

The global rise in urbanization and industrial activity has led to the production and incorporation of foreign contaminant molecules into ecosystems, distorting them and impacting human and animal health. Physical, chemical, and biological strategies have been adopted to eliminate these contaminants from water bodies under anthropogenic stress. Biotechnological processes involving microorganisms and enzymes have been used for this purpose; specifically, laccases, which are broad spectrum biocatalysts, have been used to degrade several compounds, such as those that can be found in the effluents from industries and hospitals. Laccases have shown high potential in the biotransformation of diverse pollutants using crude enzyme extracts or free enzymes. However, their application in bioremediation and water treatment at a large scale is limited by the complex composition and high salt concentration and pH values of contaminated media that affect protein stability, recovery and recycling. These issues are also associated with operational problems and the necessity of large-scale production of laccase. Hence, more knowledge on the molecular characteristics of water bodies is required to identify and develop new laccases that can be used under complex conditions and to develop novel strategies and processes to achieve their efficient application in treating contaminated water. Recently, stability, efficiency, separation and reuse issues have been overcome by the immobilization of enzymes and development of novel biocatalytic materials. This review provides recent information on laccases from different sources, their structures and biochemical properties, mechanisms of action, and application in the bioremediation and biotransformation of contaminant molecules in water. Moreover, we discuss a series of improvements that have been attempted for better organic solvent tolerance, thermo-tolerance, and operational stability of laccases, as per process requirements.

Sequential electrochemical oxidation and bio-treatment of the azo dye congo red and textile effluent

Textile effluent is often difficult to manage as it contains a high concentration of toxic and recalcitrant synthetic dyes. In this study, congo Red and textile effluent were treated by electrochemical oxidation using RuO₂-IrO₂ coated titanium electrode as an anode followed by biodecolorization using Pseudomonas stutzeri MN1 and Acinetobacter baumannii MN3. Effluent pre-treatment is often necessary to minimize the inhibitory effects of textile dyes on dye degrading bacterial during bio-treatment. The pre-treatment of Congo Red by electrochemical oxidation for 10 min resulted in a decolorization rate of 98% at a pH, NaCl concentration, and current density of 7, 2 g L^-1, and 20 mA cm^-2. Subsequent bio-treatment of the pretreated Congo Red enhanced the biodegradation to 93%. The COD removal efficiency in real textile effluent following electrochemical pretreatment and biological treatment using bacterial consortium were 3.8% and 93%, respectively. Therefore, integrating electrochemical oxidation and microbial consortia offers an effective and environmentally friendly approach for treating complex industrial effluents.