Potential of Trametes trogii culture fluids and its purified laccase for the decolorization of different types of recalcitrant dyes without the addition of redox mediators

Trametes trogii BAFC 463 culture fluids (containing 110 U ml⁻¹ laccase; 0.94 U ml⁻¹ manganese peroxidase), as well as its purified laccase were capable of decolorizing azoic, indigoid, triphenylmethane, anthraquinonic and heterocyclic dyes, in the absence of redox mediators. Six dyes: RBBR, Indigo Carmine, Xylidine, Malachite Green, Gentian Violet and Bromophenol Blue were almost completely degraded (more than 85% decolorization after 1 d) by either laccase or T. trogii itself in culture, proving the role of the enzyme in dye decolorization. The purified laccase also decolorized 65% of Fast Blue RR and 30% of Azure B and Methylene Blue after 24 h. The use of redox mediators significantly increased the decolorization rates (90% decolorization of Azure B after 1 h). 1-hydroxybenzotriazole resulted the best redox mediator, but the natural mediator p-hydroxybenzoic acid also demonstrated its efficiency for dye decolorization. Due to their ability to decolorize recalcitrant dyes without addition of redox mediators, high laccase activities, high thermostability and efficient decolorization at 70 °C and pH 7.0, even in the presence of high concentrations of heavy metals (100 mM Cu⁺², Pb⁺² or Cd⁺²) or in a synthetic dyebath, T. trogii culture fluids could be effectively used to decolorize synthetic dyes from effluents.     

Use of bitter gourd (Momordica charantia) peroxidase together with redox mediators to decolorize disperse dyes

In this study, salt fractionated bitter gourd (Momordica charantia) peroxidase was used for the decolorization of water-insoluble disperse dyes; Disperse Red 17 and Disperse Brown 1. Effect of nine different redox mediators; bromophenol, 2,4-dichlorophenol, guaiacol, 1-hydroxybenzotriazole, m-cresol, quinol, syringaldehyde, violuric acid, and vanillin on decolorization of disperse dyes by bitter gourd peroxidase has been investigated. Among these redox mediators, 1-hydroxybenzotriazole was the most effective mediator for decolorization of both the dyes by peroxidase. Bitter gourd peroxidase (0.36 U/mL) could decolorize Disperse Red 17 maximally 90% in the presence of 0.1 mM 1-hydroxybenzotriazole while Disperse Brown 1 was decolorized 65% in the presence of 0.2 mM 1-hydroxybenzotriazole. Maximum decolorization of these dyes was obtained within 1 h of incubation at pH 3.0 and temperature 40°C. The application of such enzyme plus redox mediator systems may be extendable to other recalcitrant and water insoluble synthetic dyes using novel redox mediators and peroxidases from other new and cheaper sources.     

红平菇产漆酶条件优化及对孔雀绿染料脱色的研究

采用LNAS(低氮天冬酰胺-琥珀酸)培养基添加方式,对红平菇Pleurotus djamor HP1进行培养,检测不同时间培养液对不同底物的氧化作用,进而得到光密度值的变化情况,作为漆酶的产生及活性测定的主要依据。结果表明:在含Cu2+的培养液中漆酶最大酶活为235.4 U/L。含Cu2+的培养液添加底物木屑后漆酶最大酶活为458.8 U/L。提取经优化筛选后的培养基培养出的漆酶粗酶液,对4种具有不同化学结构的染料进行了脱色试验。结果表明:三苯基甲烷类的孔雀绿在6 h时脱色率为87.5%,蒽醌类的SN4R在24 h时脱色率为49.4%,偶氮类的甲基橙在24 h时脱色率为45%,杂环类的中性红在24 h时脱色率为23.6%。因此,显示出红平菇漆酶对孔雀绿染料脱色具有较大的应用潜力,进而对废水处理具有更好的应用前景。     

Decolorization of aqueous solutions of disperse textile dyes by oxidoreductases

The potential of three oxidoreductases, a laccase preparation of Pleurotus sajor-caju PS-2001, horseradish peroxidase (HRP) and a microbial peroxidase (MP) was evaluated for the decolorization of disperse textile dyes (CI Disperse Red 343, CI Disperse Red 167 and CI Disperse Blue 148) used in polyester dyeing. Decolorization was studied in aqueous solutions varying in dye concentration, pH, temperature, enzyme concentration and the addition of mediators HBT and syringaldazine. The best conditions found for Disperse Red 343 with laccase, HRP and MP were: 15 mg L^?1 dye concentration, 50°C, pH 3.0 for laccase and pH 5.0 for peroxidases. Without mediator, the highest decolorizaton results (38.5% and 58.6%) were achieved with the highest tested concentrations of laccase (10 U mL^?1) and HRP (89.7 U mL^?1), respectively, but no significant difference in decolorization was found for the tested MP concentrations (29.9–89.7 U mL^‐1). HBT or syringaldazine increased decolorization with peroxidases significantly, but no effect was observed for the laccase. Decolorization of Disperse Red 167 (up to 15%) and Disperse Blue 148 (up to 25%) was much lower than of Disperse Red 343. With respect to enzyme concentration, the use of mediator and under the selected test conditions the laccase of P. sajor-caju PS-2001 turned out to be more efficient in disperse dye decolorization, than peroxidases HRP and MP.     

Production of a thermostable metal-tolerant laccase from Trametes versicolor and its application in dye decolorization

Production of laccase using a submerged culture of Trametes versicolor sdu-4 was optimized using a central composite design of the Response Surface Methodology. Optimized conditions gave a laccase yield of 4,213 U/L which was approximately three times of that in basal medium. The laccase was purified to homogeneity using a three-step process. The overall yield of the purification was 58%, with a purification fold of 11.4 and a specific activity of 1320.7 U/mg protein. The molecular mass of the laccase was 60 kDa. The optimum pH values of the enzyme were 2.2, 3.7, and 7 for the oxidations of ABTS, DMP, and syringaldazine, respectively. The enzyme had adaptability to a broad pH range and high temperature and wsa stable at pH 3.0 ∼ 10.0. The half-life of this laccase at 70°C was 2.2 h. Methyl red, 2-bromophenol, and 4-bromophenol were oxidized by the purified laccase in the absence of mediators. Purified laccase was effective in the decolorization of several dyes and was not inhibited by Cu²⁺, Mn²⁺, Zn²⁺, Na⁺, K⁺, Mg²⁺, Ba²⁺, and Ca²⁺ at 5 mM. These excellent characteristics made it a highly attractive candidate for industrial use.     

Dye decolorization by <Emphasis Type="Italic">Trametes hirsuta</Emphasis> immobilized into alginate beads

Summary The present paper studies the production of laccase by Trametes hirsuta immobilized into alginate beads in an airlift bioreactor. In order to enhance laccase production fresh ammonium chloride was added, which led to the production, of high laccase activities (around 1000 U l⁻¹). The bioreactor operated for 40 days without operational problems and the bioparticles maintained their shape throughout fermentation. Dye decolorization was performed at bioreactor scale operating in the batch mode. High decolorization percentages were obtained in a short time (96% for indigo carmine and 69% for phenol red in 24 h), indicating the suitability of this process for application to synthetic dye decolorization. On the other hand, in vitro decolorization of several industrial azo dyes by crude laccase produced in the above bioreactor was also performed. It was found that some of the dyes needed the addition of 1-hydroxybenzotriazole for their decolorization.     

Purification and characterization of laccase produced by a white rot fungus Pleurotus sajor-caju under submerged culture condition and its potential in decolorization of azo dyes

An extracellular laccase was isolated and purified from Pleurotus sajor-caju grown in submerged culture in a bioreactor, and used to investigate its ability to decolorize three azo dyes. The extracellular laccase production was enhanced up to 2.5-fold in the medium amended with xylidine (1 mM). Purification was carried out using ammonium sulfate (70% w/v), DEAE-cellulose, and Sephadex G-100 column chromatography. The enzyme was purified up to 10.3-fold from the initial protein preparation with an overall yield of 53%. The purified laccase was monomeric with an apparent molecular mass of 61.0 kDa. The purified enzyme exerted its optimal activity with 2,2-azino–bis(3-ethylbenzo-thiazoline-6-sulfonate (ABTS) and oxidized various lignin-related phenols. The catalytic efficiencies k _cat/K _m determined for ABTS and syringaldazine were 9.2×10⁵ and 8.7×10⁵, respectively. The optimum pH and temperature for the purified enzyme was 5.0 and 40 °C, respectively. Sodium azide completely inhibited the laccase activity. The absorption spectrum revealed type 1 and type 3 copper signals. The purified enzyme decolorized azo dyes such as acid red 18, acid Black 1, and direct blue 71 up to 90, 87, and 72%, respectively. Decolorization ability of P. sajor-caju laccase suggests that this enzyme could be used for decolorization of industrial effluents.     

Lignin-Derived Compounds as Efficient Laccase Mediators for Decolorization of Different Types of Recalcitrant Dyes

Ten phenols were selected as natural laccase mediators after screening 44 different compounds with a recalcitrant dye (Reactive Black 5) as a substrate. Their performances were evaluated at different mediator/dye ratios and incubation times (up to 6 h) by the use of Pycnoporus cinnabarinus and Trametes villosa laccases and were compared with those of eight known synthetic mediators (including -NOH- compounds). Among the six types of dyes assayed, only Reactive Blue 38 (phthalocyanine) was resistant to laccase-mediator treatment under the conditions used. Acid Blue 74 (indigoid dye), Reactive Blue 19 (anthraquinoid dye), and Aniline Blue (triarylmethane-type dye) were partially decolorized by the laccases alone, although decolorization was much more efficient and rapid with mediators, whereas Reactive Black 5 (diazo dye) and Azure B (heterocyclic dye) could be decolorized only in the presence of mediators. The efficiency of each natural mediator depended on the type of dye to be treated but, with the only exception being Azure B (<50% decolorization), nearly complete decolorization (80 to 100%) was attained in all cases. Similar rates were attained with the best synthetic mediators, but the reactions were significantly slower. Phenolic aldehydes, ketones, acids, and esters related to the three lignin units were among the best mediators, including p-coumaric acid, vanillin, acetovanillone, methyl vanillate, and above all, syringaldehyde and acetosyringone. The last two compounds are especially promising as ecofriendly (and potentially cheap) mediators for industrial applications since they provided the highest decolorization rates in only 5 to 30 min, depending on the type of dye to be treated.     

Dye decolorization by sub-tropical basidiomycetous fungi and the effect of metals on decolorizing ability

White-rot basidiomycetous fungi from sub-tropical forests plus a Phanerochaete chrysosporium control were able to decolorize several azo, triphenylmethane and heterocyclic/polymeric dyes over 14 days. The effects of metal ions on decolorizing ability towards the dye Poly-R varied. Two sub-tropical strains were capable of decolorization in the presence of up to 0.25 mM Cd²⁺, Cu²⁺ and Zn²⁺, whereas decolorization by P. chrysosporium was completely inhibited by all metals at concentrations as low as 0.1 mM. In all cases decolorizing ability was more sensitive than biomass production to metal inhibition.     

Redox-mediated decolorization of recalcitrant textile dyes by <Emphasis Type="Italic">Trichoderma harzianum</Emphasis> WL1 laccase

The efficiency of crude and partially purified Trichoderma harzianum WL1 laccase for the decolorization of synthetic dyes (Rhodamine 6G, Erioglaucine and Trypan blue) with complex aromatic structures were evaluated. Selection of dyes was based on their extensive usage in local dyeing and textile industries around the study area. Studies on the role of redox potential of laccases on dye decolorization are rarely discussed and hence, for the first time we have shown the redox mediated dye decolorizing efficiency of T. harzianum WL1 laccase with the commonly employed redox mediator 1-hydroxybenzotriazole (HBT). The process parameters such as initial dye concentration, enzyme load and HBT concentration were studied and found that they had a great influence on dye removal process. When the dyes were treated with increased concentration of enzyme, it showed a greater percentage of decolorization. Compared to the crude laccase, partially purified laccase accounts for maximum decolorization of all the dyes studied. In addition, the rate of dye decolorization was considerably enhanced in presence of 4 mM HBT. Maximum and minimum decolorization were recorded for Rhodamine 6G and Trypan blue, respectively. The results of this study further confirmed that, T. harzianum laccase was found to be suitable with HBT and this laccase-mediator system (LMS) could be applied for the decolorization of various classes of dyes.     

Lignin-derived compounds as efficient laccase mediators for decolorization of different types of recalcitrant dyes

Ten phenols were selected as natural laccase mediators after screening 44 different compounds with a recalcitrant dye (Reactive Black 5) as a substrate. Their performances were evaluated at different mediator/dye ratios and incubation times (up to 6 h) by the use of Pycnoporus cinnabarinus and Trametes villosa laccases and were compared with those of eight known synthetic mediators (including -NOH- compounds). Among the six types of dyes assayed, only Reactive Blue 38 (phthalocyanine) was resistant to laccase-mediator treatment under the conditions used. Acid Blue 74 (indigoid dye), Reactive Blue 19 (anthraquinoid dye), and Aniline Blue (triarylmethane-type dye) were partially decolorized by the laccases alone, although decolorization was much more efficient and rapid with mediators, whereas Reactive Black 5 (diazo dye) and Azure B (heterocyclic dye) could be decolorized only in the presence of mediators. The efficiency of each natural mediator depended on the type of dye to be treated but, with the only exception being Azure B (< 50% decolorization), nearly complete decolorization (80 to 100%) was attained in all cases. Similar rates were attained with the best synthetic mediators, but the reactions were significantly slower. Phenolic aldehydes, ketones, acids, and esters related to the three lignin units were among the best mediators, including p-coumaric acid, vanillin, acetovanillone, methyl vanillate, and above all, syringaldehyde and acetosyringone. The last two compounds are especially promising as ecofriendly (and potentially cheap) mediators for industrial applications since they provided the highest decolorization rates in only 5 to 30 min, depending on the type of dye to be treated.     

Influence of structure on dye degradation with laccase mediator systems

A new laccase was purified from Trametes hirsuta IMA2002. The laccase had a molecular mass of 62 kDa and an isoelectric point of pH 7. It had an optimum pH of 3.0 and an optimum temperature of 55°C. The laccase was quite stable at 30°C and pH 4.0 with a half-life of more than 100 hours. On ABTS, syringaldazide, and DMP the laccase showed K_M and K_cat values of 75, 12 and 37 μM and 64, 83 and 54 s^?1, respectively. The structurally diverse commercial dyes Indigo Carmine, Lanaset Blue 2R, Diamond Black PV 200 and Diamond Fast Brown were oxidized by the laccase. While the rate and extent of decolorization of the latter dye was significantly enhanced by the presence of different types of mediators, the structurally similar azo-dye Tartrazine was not oxidized. Lanaset Blue 2R, a commercial textile dye containing an anthrachinoid structural fragment acted similarly to anthrachinone sulfonic acid by strongly enhancing the rate of the decolorization reaction. Twenty two model azo-dyes based on the molecular framework of 2,7-dihydroxy-1-phenylazonaphtalene-3,6-disulfonic acid were synthesized and the kinetics of their laccase-catalyzed decolorization was studied. Hydroxy-substituted dyes were the most susceptible to enzyme/mediator action. All reactions were well described by Michaelis–Menten-like kinetics and the Hammett free energy linear relationship could be successfully applied to describe the influence of dye structure (substituents on the aromatic ring) on decolorization. Strongly electron withdrawing substituents such as a nitro-group in the meta-position (+0.7) resulted in positive σ-constants whereas electron donating groups such as para-methyl (?0.3) resulted in negative values for σ-constants.     

Optimization of manganese peroxidase and laccase production in the South American fungus<Emphasis Type="Italic"> Fomes sclerodermeus</Emphasis> (Lév.) Cke

Fomes sclerodermeus produces manganese peroxidase (MnP) and laccase as part of its ligninolytic system. A Doehlert experimental design was applied in order to find the optimum conditions for MnP and laccase production. The factors studied were Cu²⁺, Mn²⁺ and asparagine. The present model and data analysis allowed us not only to define optimal media for production of both laccase and MnP, but also to show the combined effects between the factors. MnP was strongly influenced by Mn²⁺, which acts as an inducer. Under these conditions Cu²⁺ negatively affected MnP activity. At 13 days of growth 0.75 U ml^–1 were produced in the optimized culture medium supplemented with 1 mM MnSO₄ and 4 g l^–1 asparagine. The laccase titer under optimized conditions reached maximum values at 16 days of growth: 13.5 U ml^–1 in the presence of 0.2 mM CuSO₄, 0.4 mM MnSO₄ and 6 g l^–1 asparagine. Mn²⁺ promoted production of both enzymes. There were important interactions among the nutrients evaluated, the most significant being those between Cu²⁺ and asparagine.     

Decolorization of simulated textile dye baths by crude laccases from Trametes hirsuta and Cerrena unicolor

In this study crude laccases from the white‐rot fungi Cerrena unicolor and Trametes hirsuta were tested for their ability to decolorize simulated textile dye baths. The dyes used were Remazol Brilliant Blue R (RBBR) (100 mg/L), Congo Red (12.5 mg/L), Lanaset Grey (75 mg/L) and Poly R‐478 (50 mg/L). The effect of redox mediators on dye decolorization by laccases was also assessed. C. unicolor laccase was able to decolorize all the dyes tested. It was especially effective towards Congo Red and RBBR with 91 and 80% of color removal in 19.5 h despite the fact that simulated textile dye baths were used. Also Poly R‐478 and Lanaset Grey were partially decolorized (69 and 48%, respectively). C. unicolor laccase did not need any mediators for removing the dyes. However, T. hirsuta laccase was only able to decolorize simulated Congo Red and RBBR dye baths (91 and 45%, respectively) in 19.5 h without mediators. When using mediators the decolorization capability was enhanced substantially, e.g. Poly R‐478 was decolorized by 78% in 25.5 h. On the whole, both laccases showed potential to be used in industrial applications.     

Differential decolorization of textile dyes in mixtures and the joint effect of laccase and cellobiose dehydrogenase activities present in extracellular extracts from Funalia trogii

The largest part of the bio-decolorization investigations have been performed to date on a single dye without exploring the behavior in complex mixtures as the real dyeing baths. Therefore, mixtures of dyes belonging to azo and anthraquinonic classes, chosen among the most utilized in textile wool dyeing, were employed for comparative enzymatic decolorization studies using the extracellular extracts from the white rot fungus Funalia trogii, to understand how the concomitant presence of more than one dye could influence their degradation course and yield.Fungal extracts containing laccase activity only were capable to partially decolorize dyes mixtures from the different classes analyzed. The deconvolution of the decolorization with time allowed to monitor the degradation of the single dyes in the mixtures evidencing a time dependent differential decolorization not observed for the singles alone. Some dyes in the blend were in fact decolorized only when the most easily converted dyes were largely transformed. These experiments would allow to help the dyeing factories in the selection of the most readily degraded dyes.Since F. trogii grown on different media and activators shows diverse levels of expression of the redox enzymes laccase and cellobiose dehydrogenase (CDH), the dyes mixtures recalcitrant to decolorization by laccase activity alone, were subjected to the combined action of extracts containing laccase and CDH. The use of CDH, in support to the activity of laccase, resulted in substantial decolorization increases (>84%) for all the refractory dyes mixtures.     

Decolorization of Victoria blue by the white rot fungus, <Emphasis Type="Italic">Phanerochaete chrysosporium</Emphasis>

Synthetic textile dyes are among the most dangerous chemical pollutants released in industrial wastewater streams. Recognizing the importance of reducing the environmental impact of these dyes, the ability of the white rot fungus Phanerochaete chrysosporium to decolorize various textile dyes was investigated. This fungus decolorized 6 of the 14 structurally diverse dyes with varying efficiency (between 14% and 52%). There was no discernable pattern of decolorization even among dyes of the same chemical class, suggesting that attack on the dyes is relatively non-specific. Among the three dyes which showed >40% decolorization, Victoria Blue B (VB) was chosen for further analysis because the ability of the fungus to decolorize VB was nearly independent over a relatively broad concentration range. Blocking lignin peroxidase (LiP) and manganese peroxidase (MnP) production by the fungus did not substantially affect VB decolorization. Inhibition of laccase production by adding various inhibitors to shaken cultures reduced VB decolorization significantly suggesting a role for laccase in VB decolorization. When sodium azide and aminotriazole were used to inhibit endogenous catalase and cytochrome P-450 oxygenase activities, there was 100% and 70% reduction in VB decolorization, respectively. Adding benzoate to trap hydrogen peroxide-derived hydroxyl radicals resulted in 50% decolorization of VB. Boiling the extracellular fluid (ECF) for 30 min resulted in approximately 50% reduction in VB decolorization. Collectively, these data suggest that laccase, and/or oxygenase/oxidase and a heat-stable non-enzymatic factor, but not Lip and MnP, play a role in VB decolorization by P. chrysosporium.     

Decolorization of reactive dyes by a thermostable laccase produced by Ganoderma lucidum in solid state culture

Dye decolorizing potential of the white rot fungus Ganoderma lucidum KMK2 was demonstrated for recalcitrant textile dyes. G. lucidum produced laccase as the dominant lignolytic enzyme during solid state fermentation (SSF) of wheat bran (WB), a natural lignocellulosic substrate. Crude enzyme shows excellent decolorization activity to anthraquinone dye Remazol Brilliant Blue R (RBBR) without redox mediator whereas diazo dye Remazol Black-5 (RB-5) requires a redox mediator. Polyacrylamide gel electrophoresis (PAGE) of crude enzyme confirms that the laccase enzyme was the major enzyme involved in decolorization of either dyes. Native and SDS-PAGE indicates that the presence of single laccase with molecular weight of 43 kDa. N-Hydroxybenzotriazole (HBT) at a concentration of 1 mM was found as the best redox mediator. RB-5 (50 mg l^−l) was decolorized by 62% and 77.4% within 1 and 2 h, respectively by the crude laccase (25 U ml⁻¹). RBBR (50 mg l^−l) was decolorized by 90% within 20 h, however, it was more efficient in presence of HBT showing 92% decolorization within 2 h. Crude laccase showed high thermostability and maximum decolorization activity at 60 °C and pH 4.0. The decolorization was completely inhibited by the laccase inhibitor sodium azide (0.5 mM). Enzyme inactivation method is a good method which averts the undesirable color formation in the reaction mixture after decolorization. High thermostability and efficient decolorization suggest that this crude enzyme could be effectively used to decolorize the synthetic dyes from effluents.     

Role of microalgal ligninolytic enzymes in industrial dye decolorization

Abstract

In this study, the decolorization efficiency of seven microalgae isolates; Nostoc muscorum, Nostoc humifusum, Spirulina platensis, Anabaena oryzae, Wollea saccata, Oscillatoria sp. and Chlorella vulgaris was investigated for dye decolorization. The highest decolorization percentages of Brazilwood, Orange G, and Naphthol Green B dyes (99.5%, 99.5%, and 98.5%, respectively) were achieved by Chlorella vulgaris. However, the maximum efficiency for dye decolorization percentages of CV and malachite green dyes were exhibited by A. oryzae (97.4%) and W. saccata (93.3%). Ligninolytic enzymes activity assay was carried out for laccase and lignin peroxidase enzymes, which revealed a high efficiency of the C. vulgaris, A. oryzae and W. saccata to lignin containing compound degradation. The highest laccase production recorded by C. vulgaris with Brazilwood, Orange G, and Naphthol Green B dyes (665.0, 678.6, and 659.5?U/ml, respectively). Similarly, C. vulgaris gave a high lignin peroxidase enzyme production with the above three dyes respectively (306.00, 298.34, and 311.45?U/ml). In addition, A. oryzae and W. saccata showed the highest production of the laccase enzyme (634.6 and 577.45?U/ml, respectively) with CV and malachite green dyes. The degradation products have been characterized after decolorization and verified using FTIR analysis. The high decolorization percentages achieved by C. vulgaris, A. oryzae and W. saccata make them potential candidates for bioremediation and pre-processing to remove dyes from textile effluents.     

Decolorization and detoxification of textile dyes using a versatile Streptomyces laccase-natural mediator system

Currently, there is increasing interest in assessing the potential of bacterial laccases for industrial and environmental applications especially in harsh conditions. The environmental impact of the textile industry requires novel and effective technologies to mitigate the presence of dyes in wastewaters before discharging into the environment. Dyes usually remain stable in the presence of a variety of chemicals, light and are recalcitrant to microbial degradation. Among available technologies the biological treatments offer environmentally friendly strategies for decolorizing and detoxifying these compounds. The recent discovery of versatile laccases in streptomycetes opens up new opportunities for their commercial application. The aim of this study is to assess the potential of a novel bacterial laccase SilA produced by Streptomyces ipomoeae CECT 3341 active over wide temperature and pH ranges for use as an eco-friendly, biological treatment for the degradation of textile dyes. Insights into the enhancement of the oxidative action of this enzyme through the use of natural redox mediators are presented together with an assessment of the potential toxicity of the degradation products. Our results confirm that the combination of the laccase and natural mediators such as acetosyringone and methyl syringate enhanced the decolorization and detoxification of a variety of textile dyes up to sixfold and 20-fold, respectively. Mediator concentration was found to have a significant effect (p < 0.05) on dye decolorization at 60 °C; thus, the decolorization of Acid Orange 63 increased from 6 to 70-fold when the mediator concentration was increased from 0.1 to 0.5 mM. Further, the toxicity of tartrazine decreased 36-fold when the SilA-MeS system was used to decolorize the dye. The thermal properties of the SilA coupled with the stability of SilA at high pH suggest a potential commercial application for use in the decolorization of textile wastewaters which generally are performed at high temperature (>55 °C) and salinity and neutral pH, conditions which are unfavourable for conventional fungal laccases.     

Enhanced transformation of malachite green by laccase of <Emphasis Type="Italic">Ganoderma lucidum</Emphasis> in the presence of natural phenolic compounds

In this study, we investigated the efficacy of phenolic extract of wheat bran and lignin-related phenolic compounds as natural redox mediators on laccase-mediated transformation of malachite green (MG) using purified laccase from the white-rot fungus Ganoderma lucidum. G. lucidum laccase was able to decolorize 40.7% MG dye (at 25 mg l⁻¹) after 24 h of incubation. Whereas, the addition of phenolic extract of wheat bran enhanced the decolorization significantly (p < 0.001) by two- to threefold than that of purified laccase alone. Among various natural phenolic compounds, acetovanillone, p-coumaric acid, ferulic acid, syringaldehyde, and vanillin were the most efficient mediators, as effective as the synthetic mediator 1-hydroxybenzotriazole. Characterization of MG transformation products by HPLC, UV–Vis, and liquid chromatography-mass spectrometry-electrospray ionization analysis revealed that N-demethylation was the key mechanism of decolorization of MG by laccase. Growth inhibition test based on mycelial growth inhibition of white rot fungus Phanerochaete chrysosporium revealed that treatment with laccase plus natural mediators effectively reduced the growth inhibitory levels of MG than that of untreated one. Among all the tested compounds, syringaldehyde showed the highest enhanced decolorization, as a consequence reduced growth inhibition was observed in syringaldehyde-treated samples. The results of the present study revealed that the natural phenolic compounds could alternatively be used as potential redox mediators for effective laccase-mediated decolorization of MG.