Fungal laccases as green catalysts for dye synthesis

Research progress on carotenoid production by Rhodosporidium toruloides

Carotenoids are natural lipophilic pigments, which have been proven to provide significant health benefits to humans, relying on their capacity to efficiently scavenge singlet oxygen and peroxyl radicals as antioxidants. Strains belonging to the genus Rhodosporidium represent a heterogeneous group known for a number of phenotypic traits including accumulation of carotenoids and lipids and tolerance to heavy metals and oxidative stress. As a representative of these yeasts, Rhodosporidium toruloides naturally produces carotenoids with high antioxidant activity and grows on a wide variety of carbon sources. As a result, R. toruloides is a promising host for the efficient production of more value-added lipophilic compound carotenoids, e.g., torulene and torularhodin. This review provides a comprehensive summary of the research progress on carotenoid biosynthesis in R. toruloides, focusing on the understanding of biosynthetic pathways and the regulation of key enzymes and genes involved in the process. Moreover, the relationship between the accumulation of carotenoids and lipid biosynthesis, as well as the stress from diverse abiotic factors, has also been discussed for the first time. Finally, several feasible strategies have been proposed to promote carotenoid production by R. toruloides. It is possible that R. toruloides may become a critical strain in the production of carotenoids or high-value terpenoids by genetic technologies and optimal fermentation processes. KEY POINTS: • Biosynthetic pathway and its regulation of carotenoids in Rhodosporidium toruloides were concluded • Stimulation of abiotic factors for carotenoid biosynthesis in R. toruloides was summarized • Feasible strategies for increasing carotenoid production by R. toruloides were proposed.

Harnessing the power of bacterial laccases for xenobiotic degradation in water: A 10-year overview

Industrialization and population growth are leading to the production of significant amounts of sewage containing hazardous xenobiotic compounds. These compounds pose a threat to human and animal health, as well as the overall ecosystem. To combat this issue, chemical, physical, and biological techniques have been used to remove these contaminants from water bodies affected by human activity. Biotechnological methods have proven effective in utilizing microorganisms and enzymes, particularly laccases, to address this problem. Laccases possess versatile enzymatic characteristics and have shown promise in degrading different xenobiotic compounds found in municipal, industrial, and medical wastewater. Both free enzymes and crude enzyme extracts have demonstrated success in the biotransformation of these compounds. Despite these advancements, the widespread use of laccases for bioremediation and wastewater treatment faces challenges due to the complex composition, high salt concentration, and extreme pH often present in contaminated media. These factors negatively impact protein stability, recovery, and recycling processes, hindering their large-scale application. These issues can be addressed by focusing on large-scale production, resolving operation problems, and utilizing cutting-edge genetic and protein engineering techniques. Additionally, finding novel sources of laccases, understanding their biochemical properties, enhancing their catalytic activity and thermostability, and improving their production processes are crucial steps towards overcoming these limitations. By doing so, enzyme-based biological degradation processes can be improved, resulting in more efficient removal of xenobiotics from water systems. This review summarizes the latest research on bacterial laccases over the past decade. It covers the advancements in identifying their structures, characterizing their biochemical properties, exploring their modes of action, and discovering their potential applications in the biotransformation and bioremediation of xenobiotic pollutants commonly present in water sources.

Theoretical insights into the mechanism underlying aflatoxin B1 transformation by the BsCotA-methyl syringate system

Global concern exists regarding the contamination of food and animal feed with aflatoxin B1 (AFB1), which poses a threat to the health of both humans and animals. Previously, we found that a laccase from Bacillus subtilis (BsCotA) effectively detoxified AFB1 in a reaction mediated by methyl syringate (MS), although the underlying mechanism has not been determined. Therefore, our primary objective of this study was to explore the detoxification mechanism employed by BsCotA. First, the enzyme and mediator dependence of AFB1 transformation were studied using the BsCotA-MS system, which revealed the importance of MS radical formation during the oxidation process. Aflatoxin Q1 (AFQ1) resulting from the direct oxidation of AFB1 by BsCotA, was identified using ultra-high-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The results of UPLC-MS/MS and density functional theory calculations indicated that the products included AFQ1, AFB1-, and AFD1-MS-coupled products in the BsCotA-MS system. The toxicity evaluations revealed that the substances derived from the transformation of AFB1 through the BsCotA-MS mechanism exhibited markedly reduced toxicity compared to AFB1. Finally, we proposed a set of different AFB1-transformation pathways generated by the BsCotA-MS system based on the identified products. These findings greatly enhance the understanding of the AFB1-transformation mechanism of the laccase-mediator system.

Fungal Laccases: Fundamentals, Engineering and Classification Update

Multicopper oxidases (MCOs) share a common catalytic mechanism of activation by oxygen and cupredoxin-like folding, along with some common structural determinants. Laccases constitute the largest group of MCOs, with fungal laccases having the greatest biotechnological applicability due to their superior ability to oxidize a wide range of aromatic compounds and lignin, which is enhanced in the presence of redox mediators. The adaptation of these versatile enzymes to specific application processes can be achieved through the directed evolution of the recombinant enzymes. On the other hand, their substrate versatility and the low sequence homology among laccases make their exact classification difficult. Many of the ever-increasing amounts of MCO entries from fungal genomes are automatically (and often wrongly) annotated as laccases. In a recent comparative genomic study of 52 basidiomycete fungi, MCO classification was revised based on their phylogeny. The enzymes clustered according to common structural motifs and theoretical activities, revealing three novel groups of laccase-like enzymes. This review provides an overview of the structure, catalytic activity, and oxidative mechanism of fungal laccases and how their biotechnological potential as biocatalysts in industry can be greatly enhanced by protein engineering. Finally, recent information on newly identified MCOs with laccase-like activity is included.

Identification of laccase genes in Trichoderma asperellum Ts93

Although extensive research efforts have been dedicated to characterizing the laccase from white-rot fungus, little information is available on laccases from Trichoderma spp. A copper-tolerant strain with the ability to produce laccase was isolated and identified as Trichoderma asperellum Ts93. Under optimized conditions, the maximum laccase activity was 1.96 U/ml. The genome-wide survey of Ts93 revealed the presence of seven putative laccase genes that all contained the conserved domain and were divided into three different phylogenetic groups. Among these genes, three contained the four copper-binding conserved regions. The expression profiles acquired through real-time quantitative PCR analysis showed that five of the seven genes were significantly upregulated in response to laccase activity. Seven laccase genes in T. asperellum were identified for the first time by whole-genome sequencing followed by phylogenetic analysis. The findings of this work provide valuable information for the functional analysis of laccase genes in Trichoderma spp.

Potential of the enzyme laccase for the synthesis and derivatization of antimicrobial compounds

Laccases [E.C. 1.10.3.2, benzenediol:dioxygen oxidoreductase] can oxidize phenolic substances, e.g. di- and polyphenols, hydroxylated biaryls, aminophenols or aryldiamines. This large substrate spectrum is the basis for various reaction possibilities, which include depolymerization and polymerization reactions, but also the coupling of different substance classes. To catalyze these reactions, laccases demand only atmospheric oxygen and no depletive cofactors. The utilization of mild and environmentally friendly reaction conditions such as room temperature, atmospheric pressure, and the avoidance of organic solvents makes the laccase-mediated reaction a valuable tool in green chemistry for the synthesis of biologically active compounds such as antimicrobial substances. In particular, the production of novel antibiotics becomes vital due to the evolution of antibiotic resistances amongst bacteria and fungi. Therefore, laccase-mediated homo- and heteromolecular coupling reactions result in derivatized or newly synthesized antibiotics. The coupling or derivatization of biologically active compounds or its basic structures may allow the development of novel pharmaceuticals, as well as the improvement of efficacy or tolerability of an already applied drug. Furthermore, by the laccase-mediated coupling of two different active substances a synergistic effect may be possible. However, the coupling of compounds that have no described efficacy can lead to biologically active substances by means of laccase. The review summarizes laccase-mediated reactions for the synthesis of antimicrobial compounds valuable for medical purposes. In particular, reactions with two different reaction partners were shown in detail. In addition, studies with in vitro and in vivo experimental data for the confirmation of the antibacterial and/or antifungal efficacy of the products, synthesized with laccase, were of special interest. Analyses of the structure-activity relationship confirm the great potential of the novel compounds. These substances may represent not only a value for pharmaceutical and chemical industry, but also for other industries due to a possible functionalization of surfaces such as wood or textiles.

Recent Advancements in Biotechnological Applications of Laccase as a Multifunctional Enzyme

Biotechnological and industrial processes involve applications of various microorganisms and enzymes, and laccase, as a multifunctional enzyme, is admired for its role in degrading a variety of substances. Laccase is a copper-containing oxidase enzyme that is usually found in insects, plants, and microorganisms including fungi and archaea. Several phenolic substrates are oxidized by laccases, which results in crosslinking. Various research work and industrial solutions have identified the true potential of laccases to degrade various aromatic polymers, and their plausible application in bioremediation and other industries is entirely conceivable. This review focuses on laccases as a multifunctional enzyme and provides an overview of its natural origin, catalytic mechanism, and various methods of production. Further, we discuss the various applications of laccase in the biotechnological arena. We observed that laccase can degrade and detoxify various synthetic compounds. The broad substrate specificity of the same makes it worthy for different fields of industrial applications such as food and bioremediation technology, textile and paper technology, biosensors and nanobiotechnology, biofuel, and various other applications, which are described in this paper. These recent developments in the application of laccase show the multifunctional role of laccase in industrial biotechnology and provide an outlook of laccase as a multifunctional enzyme at the forefront of biotechnology.

Novel laccase from Xylaria polymorpha and its efficiency in the biotransformation of pharmaceuticals: Optimization of operational conditions, comparative effect of redox-mediators and toxicity studies

The promising potentials of biocatalytic treatment processes in the removal of micropollutants whilst eliminating health and environmental hazards have attracted great attention in recent years. This current work investigated the biotransformation efficiency of a novel laccase from Xylaria polymorpha (XPL) in comparison with commercial laccases from Trametes versicolor (TVL) and Aspergillus sp. (ASL). XPL exhibited better oxidation performance (95.7%) on AMX than TVL (92.8%) and ASL (90.5%). Optimization of operational conditions revealed that AMX was best oxidized at pH 5, temperature (30 °C), and concentration (1.0 mg L^-1). The investigation carried out to determine the effect of redox mediators revealed violuric acid (VLA) as the best redox mediator. The laccase stability experiments elucidated that the oxidation of AMX is time and mediator concentration dependent with ABTS exhibiting highest deactivation of XPL active sites. Two metabolic products; amoxicillin penilloic acid and 5-hydroxy-6-(4-hydroxyphenyl)- 3-(1,3-thiazolidin-2-yl)piperazin-2-one of AMX were obtained through Liquid Chromatography-Mass Spectrometry (LC-MS) analyses. The toxicity assessments carried out after oxidation of AMX by XPL showed 94% and 97% reduced toxicity on Artemia salina and Aliivibrio fischeri respectively. The study further underscored the efficiency of biocatalytic-mediator technology in the transformation of complex micropollutants into less toxic substances in an eco-friendly way.

Current research progress on laccase-like nanomaterials

The first systematic review of the progress of research on the types and applications of laccase-like activity of nanomaterials is reported.

Thermostable bacterial laccase for sustainable dyeing using plant phenols

Laccase is regarded as an efficacious eco-friendly enzyme in various industries. Thus, various laccases have been explored to mitigate the environmental effects of conventional industrial processing; however, the prospects of laccase in hair dyeing have not been thoroughly explored to date. On account of the adverse environmental and health-related issues posed by chemical hair dyeing, laccase as a natural alternative in dyeing hair has recently gained attention. In this study, we executed hair dyeing with different colours and shades of hair dyes developed from natural plant phenols, including ferulic acid, gallic acid, catechol, and syringaldehyde, catalysed by a novel thermostable bacterial laccase (LacT) from Brevibacillus agri. The dyed hair was characterised in terms of its colourimetric parameters (L*, a*, and b*), colour strength (K/S), reflectance (R) and colour durability. L* means luminosity and is defined by L* values from 0 (black) to 100 (white). A positive value of a* means red shades and a negative value indicates green shades. A positive value of b* shows yellow shades and a negative value indicates blue shades. Optical microscopy of circular and longitudinal sections of the dyed hair revealed that the laccase-catalysed dyes did not merely stick to the surface; instead, they well-penetrated the hair. Furthermore, the dyeing process did not affect the surface morphology of the dyed hair. The dyed hair also exhibited a desirable range of colour diversity in terms of market-driven demands and showed considerable resistance to fading during shampooing and pH alterations. Post-dyeing, the texture and tensile strength of the dyed hair remained nearly unchanged. Overall, the outcomes suggest that LacT holds high potential to be exploited extensively in the hair dyeing industry as an alternative to chemical hair dyes.

Laccase is regarded as an efficacious eco-friendly enzyme in various industries.

Advances in laccase-triggered anabolism for biotechnology applications

This is the first comprehensive overview of laccase-triggered anabolism from fundamental theory to biotechnology applications. Laccase is a typical biological oxidordeuctase that induces the one-electronic transfer of diverse substrates for engendering four phenoxy radicals with concomitant reduction of O₂ into 2H₂O. In vivo, laccase can participate in anabolic processes to create multifarious functional biopolymers such as fungal pigments, plant lignins, and insect cuticles, using mono/polyphenols and their derivatives as enzymatic substrates, and is thus conducive to biological tissue morphogenesis and global carbon storage. Exhilaratingly, fungal laccase has high redox potential (E° = 500-800 mV) and thermodynamic efficiency, making it a remarkable candidate for utilization as a versatile catalyst in the green and circular economy. This review elaborates the anabolic mechanisms of laccase in initiating the polymerization of natural phenolic compounds and their derivatives in vivo via radical-based self/cross-coupling. Information is also presented on laccase immobilization engineering that expands the practical application ranges of laccase in biotechnology by improving the enzymatic catalytic activity, stability, and reuse rate. Particularly, advances in biotechnology applications in vitro through fungal laccase-triggered macromolecular biosynthesis may provide a key research direction beneficial to the rational design of green chemistry.

Antimicrobial Activity and Barrier Properties against UV Radiation of Alkaline and Enzymatically Treated Linen Woven Fabrics Coated with Inorganic Hybrid Material

One of the directions of development in the textiles industry is the search for new technologies for producing modern multifunctional products. New solutions are sought to obtain materials that will protect humans against the harmful effects of the environment, including such factors as the activity of microorganisms and UV radiation. Products made of natural cellulose fibers are often used. In the case of this type of material, it is very important to perform appropriate pretreatment before subsequent technological processes. This treatment has the aim of removing impurities from the surface of the fibers, which results in the improvement of sorption properties and adhesion, leading directly to the better penetration of dyes and chemical modifiers into the structure of the materials. In this work, linen fabrics were subjected to a new, innovative treatment being a combination of bio-pretreatment using laccase from Cerrena unicolor and modification with CuO-SiO₂ hybrid oxide microparticles by a dip-coating method. To compare the effect of alkaline or enzymatic pretreatment on the microstructure of the linen woven fabrics, SEM analysis was performed. The new textile products obtained after this combined process exhibit very good antimicrobial activity against Candida albicans, significant antibacterial activity against the Gram-negative Escherichia coli and the Gram-positive Staphylococcus aureus, as well as very good UV protection properties (ultraviolet protection factor (UPF) > 40). These innovative materials can be used especially for clothing or outdoor textiles for which resistance to microorganisms is required, as well as to protect people who are exposed to long-term, harmful effects of UV radiation.

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.

FTacV study of electroactive immobilized enzyme/free substrate reactions: Enzymatic catalysis of epinephrine by a multicopper oxidase from Thermothelomyces thermophila

In the present work, a kinetic analysis is made concerning the reaction of an electroactive immobilized enzyme with a free substrate, based on a Michaelis-Menten scheme. The proposed kinetic equations are investigated numerically for conditions describing large amplitude fast Fourier transform alternating current voltammetry (FTacV), under different reaction states (transient or steady state for the reaction intermediate as well as quasi or complete reversibility of the electrochemical step). The dependence of two chief observables that occur from the analysis of the results of the method, that is, the maximum of the harmonics and the potential shift of the corresponding dominant peaks, on substrate concentration is presented. The FTacV method is applied experimentally for an immobilized laccase-like multicopper oxidase from Thermothelomyces thermophila, TtLMCO1, and its reaction with epinephrine. From the experimental findings it is shown that the intrinsic characteristics of the system do not lead to the extraction of the desired kinetic data although indications on the relation between the kinetic constants is revealed. Finally, the response of the third harmonic for the first additions of epinephrine at subnanomolarity range can be exploited for the detection of epinephrine at rather low concentrations.

Oxalate oxidase from Abortiporus biennis - protein localisation and gene sequence analysis

We have described for the first time the localisation of oxalate oxidase (OXO, EC 1.2.3.4) in Abortiporus biennis cells, using histochemical and immunochemical methods coupled with transmission electron microscopy. Rabbit anti-oxalate oxidase immunoglobulins with anti-rabbit secondary antibody conjugated with 10-nm gold particles were used. Moreover, the formation of electron dense precipitation of reaction of diaminobenzidine (DAB) with horseradish peroxidase (HRP) for histochemical localisation of the enzyme was found. OXO was localised close to the membranous structures of the cell membranes, in membranous vesicles located close to the outer cell membrane, and vacuolar membranes surrounding vacuoles. The positive immunoreaction to OXO was also intense in cell wall areas. Moreover, we proved that gene coding for OXO was expressed in the same cultures. Corresponding mRNA was isolated, full length cDNA was synthesized, cloned and sequenced. Two copies of cupin domains were found in the sequence of amino-acids conserved domain coding for the cupin enzyme. Comparison of the genomic DNA and cDNA sequences has revealed the presence of seventeen introns in the gene. The isoelectric point of the protein was estimated at pH 4.5 and several possible N-glycosylation sites were predicted.

Structure and Bioactive Properties of Novel Textile Dyes Synthesised by Fungal Laccase

Novel sustainable processes involving oxidative enzymatic catalysts are considered as an alternative for classical organic chemistry. The unique physicochemical and bioactive properties of novel bio-products can be obtained using fungal laccase as catalyst. Among them are textile biodyes synthesised during oxidation of substrates belonging to the amine and methoxy organic derivatives. The process of synthesis occurs in mild conditions of pH, temperature, and pressure, and without using harmful oxidants. The effect of fungal laccase activity on the substrates mixture transformation efficiency was analysed in terms of antimicrobial dye synthesis on a large scale. Three new phenazine dyes, obtained in the presence of laccase from Cerrena unicolor, were studied for their structure and properties. The phenazine core structure of the products was a result of tri-molecular transformation of aminomethoxybenzoic acid and aminonaphthalene sulfonic acid isomers. One of the compounds from the synthesised dye, namely 10-((2-carboxy-6-methoxyphenyl)amino)-11-methoxybenzo[a]phenazine-8-carboxylic acid, was able to inhibit the growth of Staphylococcus aureus. The high concentration of substrates (5 g/L) was efficiently transformed during 72 h in the mild conditions of pH 4 with the use of laccase with an activity of 200 U per g of the substrates mixture. The new bioactive dye exhibited excellent dyeing properties with concomitant antibacterial and antioxidative activity. The proposed enzyme-mediated synthesis represents an alternative eco-friendly route for the synthesis of novel antimicrobial compounds with high importance for the medical textile industry.

Genome sequence of the fungus Pycnoporus sanguineus, which produces cinnabarinic acid and pH- and thermo- stable laccases

Pycnoporus sanguineus, an edible mushroom, produces antimicrobial and antitumor bioactive compounds and pH- and thermo- stable laccases that have multiple potential biotechnological applications. Here we reported the complete genome of the species Pycnoporus sanguineus ACCC 51,180 by using the combination of Illumina HiSeq X Ten and the PacBio sequencing technology. The represented genome is 36.6 Mb composed of 59 scaffolds with 12,086 functionally annotated protein-coding genes. The genome of Pycnoporus sanguineus encodes at least 19 biosynthetic gene clusters for secondary metabolites, including a terpene cluster for biosynthesis of the antitumor clavaric acid. Seven laccases were identified, while 22 genes were found to be involved in the kynurenine pathway in which the intermediate metabolite 3-hydroxyanthranilic acid were catalyzed by laccases into cinnabarinic acid. This study represented the third genome of the genus Pycnoporus, and wound facilitate the exploration of useful sources from Pycnoporus sanguineus for future industrial applications.

Mold resistance of bamboo after laccase-catalyzed attachment of thymol and proposed mechanism of attachment

Laccase-catalyzed attachment of functional molecules onto the surface of bamboo represents an alternative, green approach to improve performance. Although treatment of bamboo with thymol improved resistance to mold, using laccase to fix the same concentration of thymol to the surface of the bamboo could increase both the antifungal activity and resistance to leaching. Leaching of thymol was reduced by as much as 48.4% when laccase was used in thymol fixation. To make clear the mechanisms of fixation, reaction of thymol catalyzed with laccase, was investigated using Fourier-transform infrared spectroscopy, ¹H-NMR, high-resolution mass spectrometry and thermogravimetric analysis, respectively. Results show that thymol oligomer (l-thymol) was formed with ether linkages, which resist water leaching. Although further confirmatory studies are needed, it seems that ether linkages were the main connection of thymol to lignin. This study demonstrates that laccase catalysis is a promising strategy to functionalize the surface of bamboo in order to bestow new properties suitable for a wide range of applications.

Schematic diagram of laccase-catalysed fixation of natural antimicrobial phenol to bamboo.

Applications of Microbial Laccases: Patent Review of the Past Decade (2009–2019)

There is a high number of well characterized, commercially available laccases with different redox potentials and low substrate specificity, which in turn makes them attractive for a vast array of biotechnological applications. Laccases operate as batteries, storing electrons from individual substrate oxidation reactions to reduce molecular oxygen, releasing water as the only by-product. Due to society’s increasing environmental awareness and the global intensification of bio-based economies, the biotechnological industry is also expanding. Enzymes such as laccases are seen as a better alternative for use in the wood, paper, textile, and food industries, and they are being applied as biocatalysts, biosensors, and biofuel cells. Almost 140 years from the first description of laccase, industrial implementations of these enzymes still remain scarce in comparison to their potential, which is mostly due to high production costs and the limited control of the enzymatic reaction side product(s). This review summarizes the laccase applications in the last decade, focusing on the published patents during this period.

Novel textile dye obtained through transformation of 2-amino-3-methoxybenzoic acid by free and immobilised laccase from a Pleurotus ostreatus strain

Transformation of 2-amino-3-methoxybenzoic acid into novel and eco-friendly orange dye (N15) was performed using native and immobilised laccase (LAC) from Pleurotus ostreatus strain. A several parameters affecting laccase-mediated transformation efficiency included the selection of type and pH value of buffer, reaction temperature, substrate and laccase concentration as well as the type of carrier and LAC storage conditions were evaluated. The optimal conditions for N15 dye synthesis were 40 mM sodium-tartrate buffer pH 5.5 containing 3 mM of the substrate, efficiently transformed by 2 U of free laccase per 1 mmol of the substrate. Laccase was immobilised on porous Purolite® carriers, which had never been tested as a support for oxidoreductases. Immobilised laccase, characterised by a high immobilisation yield, was obtained by adsorption of laccase on a porous acrylic carrier with octadecyl groups (C₁₈) incubated in optimum conditions of 40 mM phosphate buffer pH 7.0 containing 1 mg of laccase per 1 g of the carrier (wet mass). The immobilised LAC showed the highest storage stability for 21 days and higher thermostability at 40 ℃ and 60 ℃ in comparison to its native form. The N15 dye showed good dyeing properties towards natural fibres, and the dyed fibre demonstrated resistance to different physicochemical factors during use, which was confirmed by commercial quality tests. The N15 dye is a phenazine, i.e. a heterogenic compound containing amino-, methoxy-, and three carboxyl functional groups with the molecular weight of approximately 449.37 U.

Synthesizing Polyaniline With Laccase/O2 as Catalyst

The polymerization of aniline to polyaniline (PANI) can be achieved chemically, electrochemically or enzymatically. In all cases, the products obtained are mixtures of molecules which are constituted by aniline units. Depending on the synthesis conditions there are variations (i) in the way the aniline molecules are connected, (ii) in the average number of aniline units per molecule, (iii) in the oxidation state, and (iv) in the degree of protonation. For many possible applications, the synthesis of electroconductive PANI with para-N-C-coupled aniline units in their half-oxidized and protonated state is of interest. This is the emeraldine salt form of PANI, abbreviated as PANI-ES. The enzymatic synthesis of PANI-ES is an environmentally friendly alternative to conventional chemical or electrochemical methods. Although many studies have been devoted to the in vitro synthesis of PANI-ES by using heme peroxidases with added hydrogen peroxide (H2O2) as the oxidant, the application of laccases is of particular interest since the oxidant for these multicopper enzymes is molecular oxygen (O2) from air, which is beneficial from environmental and economic points of view. In vivo, laccases participate in the synthesis and degradation of lignin. Various attempts of synthesizing PANI-ES with laccase/O2 in slightly acidic aqueous media from aniline or the linear aniline dimer PADPA (p-aminodiphenylamine) are summarized. Advances in the understanding of the positive effects of soft dynamic templates, as chemical structure guiding additives (anionic polyelectrolytes, micelles, or vesicles), for obtaining PANI-ES-rich products are highlighted. Conceptually, some of these template effects appear to be related to the effect "dirigent proteins" exert in the biosynthesis of lignin. In both cases intermediate radicals are formed enzymatically which then must react in a controlled way in follow-up reactions for obtaining the desired products. These follow-up reactions are controlled to some extent by the templates or specific proteins.

Aptitude of Oxidative Enzymes for Treatment of Wastewater Pollutants: A Laccase Perspective

Natural water sources are very often contaminated by municipal wastewater discharges which contain either of xenobiotic pollutants and their sometimes more toxic degradation products, or both, which frustrates the universal millenium development goal of provision of the relatively scarce pristine freshwater to water-scarce and -stressed communities, in order to augment their socioeconomic well-being. Seeing that both regulatory measures, as regards the discharge limits of wastewater, and the query for efficient treatment methods remain unanswered, partially, the prospects of enzymatic treatment of wastewater is advisable. Therefore, a reconsideration was assigned to the possible capacity of oxidative enzymes and the respective challenges encountered during their applications in wastewater treatment, and ultimately, the prospects of laccase, a polyphenol oxidase that oxidizes aromatic and inorganic substrates with electron-donating groups in treatment aromatic contaminants of wastewater, in real wastewater situations, since it is assumed to be a vehicle for a greener community. Furthermore, the importance of laccase-driven catalysis toward maintaining mass-energy balance, hence minimizing environmental waste, was comprehensibly elucidated, as well the strategic positioning of laccase in a model wastewater treatment facility for effective treatment of wastewater contaminants.

Synthesis of Azobenzene Dyes Mediated by CotA Laccase

An eco-friendly protocol for the synthesis of azobenzene dyes by oxidative coupling of primary aromatic amines is reported. As efficient biocatalytic systems, CotA laccase and CotA laccase/ABTS (2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid)) enable the oxidation of various substituted anilines, in aqueous medium, ambient atmosphere and under mild reaction conditions of pH and temperature. A series of azobenzene dyes were prepared in good to excellent yields in an one-pot reaction. A mechanistic proposal for the formation of the azo derivatives is presented. Our strategy offers an alternative approach for the direct synthesis of azobenzene dyes, avoiding the harsh conditions generally required for most of the traditional synthetic methods.

Potential of Trichoderma koningii to eliminate alachlor in the presence of copper ions

The filamentous fungus Trichoderma koningii is capable of fast and effective eliminate alachlor (90% after 72 h when added separately and 80-60% in the presence of 1-5 mM of copper). After 168 h over 99% elimination of alachlor resulted in detoxification and was connected with the mitigation of reactive oxygen species (ROS) production. Using MS/MS techniques, seven dechlorinated and hydroxylated metabolites were identified. Cytochrome P450 and laccase participate in biotransformation of the herbicide by this non-ligninolytic fungus. Laccase activity is stimulated both by copper and the mixture of copper and alachlor, which seems to be important for combined pollutants. T. koningii is characterized by high tolerance to copper (up to 7.5 mM). The metal content in mycelia reached 0.9-7.76 mg in 1 g of dry biomass. Our results suggest that T. koningii strain seems to be a promising tool for bioremediation of agricultural areas co-contaminated with copper-based fungicides and chloroacetanilide herbicides.

Laccase-Mediated Grafting on Biopolymers and Synthetic Polymers: A Critical Review

Laccase-mediated grafting on lignocelluloses has gained considerable attention as an environmentally benign method to covalently modify wood, paper and cork. In recent decades this technique has also been employed to modify fibres with a polysaccharide backbone, such as cellulose or chitosan, to infer colouration, antimicrobial activity or antioxidant activity to the material. The scope of this approach has been further widened by researchers, who apply mediators or high redox potential laccases and those that modify synthetic polymers and proteins. In all cases, the methodology relies on one- or two-electron oxidation of the surface functional groups or of the graftable molecule in solution. However, similar results can very often be achieved through simple deposition, even after extensive washing. This unintended adsorption of the active substance could have an adverse effect on the durability of the applied coating. Differentiating between actual covalent binding and adsorption is therefore essential, but proves to be challenging. This review not only covers excellent research on the topic of laccase-mediated grafting over the last five to ten years, but also provides a critical comparison to highlight either the lack or presence of compelling evidence for covalent grafting.

Preparation of Biocolorant and Eco-Dyeing Derived from Polyphenols Based on Laccase-Catalyzed Oxidative Polymerization

Natural products have been believed to be a promising source to obtain ecological dyes and pigments. Plant polyphenol is a kind of significant natural compound, and tea provides a rich source of polyphenols. In this study, biocolorant derived from phenolic compounds was generated based on laccase-catalyzed oxidative polymerization, and eco-dyeing of silk and wool fabrics with pigments derived from tea was investigated under the influence of pH variation. This work demonstrated that the dyeing property was better under acidic conditions compared to alkalinity, and fixation rate was the best when pH value was 3. Furthermore, breaking strength of dyed fabrics sharply reduced under the condition of pH 11. Eventually, the dyeing method was an eco-friendly process, which was based on bioconversion, and no mordant was added during the process of dyeing.

Laccase-mediated functionalization of chitosan with 4-hexyloxyphenol enhances antioxidant and hydrophobic properties of copolymer

An effective method to functionalize chitosan with 4-hexyloxyphenol (HP) under homogeneous reaction conditions was developed using laccase as the catalyst. The resulting copolymer was characterized for chemical structure, grafted-HP content, surface morphology, thermal stability, antioxidant capacity, hydrophobic properties and tensile strength. Solid-state ¹³C NMR spectrum confirmed the incorporation of HP onto chitosan. X-ray diffraction (XRD) showed a decrease in the degree of crystallinity for laccase/HP treated chitosan compared to pure chitosan. The grafted-HP content in laccase/HP-treated chitosan first increased and then declined with increase of the initial HP/chitosan ratio. A heterogeneous surface with spherical particles on the laccase/HP treated chitosan was observed by environmental scanning electron microscopy (ESEM) and scanning probe microscopy (SPM). The laccase/HP treatment of chitosan improved the thermal stability of copolymer. More significantly, the HP functionalized chitosan showed greatly improved ABTS⁺ and DPPH radicals scavenging capacity, compared with pure chitosan. The hydrophobicity property of the HP functionalized chitosan also significantly increased although its tensile strength decreased. This new type of composite with double functionalities (i.e., antioxidant and hydrophobic) could potentially be used as food packaging materials or coating agents.

Laccase: a multi-purpose biocatalyst at the forefront of biotechnology

Laccases are multicopper containing enzymes capable of performing one electron oxidation of a broad range of substrates. Using molecular oxygen as the final electron acceptor, they release only water as a by-product, and as such, laccases are eco-friendly, versatile biocatalysts that have generated an enormous biotechnological interest. Indeed, this group of enzymes has been used in different industrial fields for very diverse purposes, from food additive and beverage processing to biomedical diagnosis, and as cross-linking agents for furniture construction or in the production of biofuels. Laccases have also been studied intensely in nanobiotechnology for the development of implantable biosensors and biofuel cells. Moreover, their capacity to transform complex xenobiotics makes them useful biocatalysts in enzymatic bioremediation. This review summarizes the most significant recent advances in the use of laccases and their future perspectives in biotechnology.

Laccase: a green catalyst for the biosynthesis of poly-phenols

Laccases (benzene diol: oxidoreductases, EC 1.10.3.2) are able to catalyze the oxidation of various compounds containing phenolic and aniline structures using dissolved oxygen in water. Laccase structural features and catalytic mechanisms focused on the polymerization of aromatic compounds are reported. A description about the most recent research on the biosynthesis of chemicals and polymers is made. Selected applications of this technology are considered as well as the advantages, shortcomings and future needs related with the use of laccases.