Ligninolytic Fungal Laccases and Their Biotechnological Applications

Basidiomycota strains as whole-cell biocatalysts for the synthesis of high-value natural benzaldehydes

Substituted benzaldehydes are the most commonly used natural-occurring flavours in the world. The consumer's preference for 'natural or organic' aromas has increased the request for flavours possessing the 'natural' status. The resulting shortage of aromatic aldehydes of extractive origin, such as vanillin, veratraldehyde and piperonal, can be offset by developing a new biotechnological synthesis method. Here, we report a study on the microbiological reduction of five natural benzoic acid derivatives, namely p-anisic, vanillic, veratric, piperonylic and eudesmic acids, to produce the corresponding fragrant aldehydes. We found that different Basidiomycota strains can efficiently perform this transformation, with good chemical selectivity and tolerance to the toxicity of substrates and products. Besides confirming the carboxylic acid reductase activity of the already studied fungi Pycnoporus cinnabarinus, we discovered that other species such as Pleurotus eryngii, Pleurotus sapidus and Laetiporus sulphureus as well as the non-ligninolytic fungi Lepista nuda are valuable microorganisms for the synthesis of anisaldehyde, vanillin, veratraldehyde, piperonal and 3,4,5-trimethoxybenzaldehyde from the corresponding acids. According to our findings, we propose a reliable process for the preparation of the above-mentioned aldehydes, in natural form. KEY POINTS: • Fragrant benzaldehydes were obtained by biotransformation. • Basidiomycota strains reduced substituted benzoic acid to the corresponding aldehydes. • Anisaldehyde, vanillin, veratraldehyde, piperonal and 3,4,5-trimethoxybenzaldehyde were prepared in natural form.

Assessment of the chemical composition of buriti (Mauritia flexuosa Liliopsida) and cassava (Manihot esculenta Crantz) residues and their possible application in the bioproduction of coconut aroma (6 pentyl-α-pyrone)

This work aimed to define strategies to increase the bioproduction of 6 pentyl-α-pyrone (bioaroma). As first strategy, fermentations were carried out in the solid state, with agro-industrial residues: Mauritia flexuosa Liliopsida. and Manihot esculenta Crantz in isolation, conducting them with different nutrient solutions having Trichoderma harzianum as a fermenting fungus. Physicochemical characterizations, centesimal composition, lignocellulosic and mineral content and antimicrobial activity were required. Fermentations were conducted under different humidification conditions (water, nutrient solution without additives and nutrient solutions with glucose or sucrose) for 9 days. Bioaroma was quantified by gas chromatography, assisted by solid-phase microextraction. The results showed the low production of this compound in fermentations conducted with sweet cassava (around 6 ppm (w/w)). The low bioproduction with sweet cassava residues can probably be related to its starch-rich composition, homogeneous substrate, and low concentration of nutrients. Already using buriti, the absence of aroma production was detected. Probably the presence of silicon and high lignin content in buriti minimized the fungal activity, making it difficult to obtain the aroma of interest. Given the characteristics presented by the waste, a new strategy was chosen: mixing waste in a 1:1 ratio. This fermentation resulted in the production of 156.24 ppm (w/w) of aroma using the nutrient solution added with glucose. This combination, therefore, promoted more favorable environment for the process, possibly due to the presence of fermentable sugars from sweet cassava and fatty acids from the buriti peel, thus proving the possibility of an increase of around 2500% in the bioproduction of coconut aroma.

Laccase: Sustainable production strategies, heterologous expression and potential biotechnological applications

Laccase is a multicopper oxidase enzyme that target different types of phenols and aromatic amines. The enzyme can be isolated and characterized from microbes, plants and insects. Its ubiquitous nature and delignification ability makes it a valuable tool for research and development. Sustainable production methods are being employed to develop low cost biomanufacturing of the enzyme while achieving high titers. Laccase have significant industrial application ranging from food industry where it can be used for wine stabilization, texture improvement and detection of phenolic compounds in food products, to cosmetics offering benefits such as skin brightening and hair colouring. Dye decolourization/degradation, removal of pharmaceutical products/emerging pollutants and hydrocarbons from wastewater, biobleaching of textile fabrics, biofuel production and delignification of biomass making laccase a promising green biocatalyst. Innovative methods such as using inducers, microbial co-culturing, recombinant DNA technology, protein engineering have pivotal role in developing laccase with tailored properties. Enzyme immobilization using new age compounds including nanoparticles, carbonaceous components, agro-industrial residues enhance activity, stability and reusability. Commercial formulations of laccase have been prepared and readily available for a variety of applications. Certain challenges including production cost, metabolic stress in response to heterologous expression, difficulty in purification needs to be addressed.

Expression profiling of laccase and β-glucan synthase genes in Pleurotus ostreatus during different developmental stages

BACKGROUND

Pleurotus ostreatus, commonly known as the oyster mushroom, is a saprophytic fungus with many applications in biotechnology and medicine. This mushroom is a rich source of proteins, polysaccharides, and bioactive compounds that have been shown to possess anticancer, antioxidant, and immunomodulatory properties. In this study, we investigated the expression profile of laccase (POXA3) and β-glucan synthase (FKS) genes during different developmental stages in two strains of P. ostreatus.

METHODS AND RESULTS

Cultural and morphological studies of the two strains were studied. DMR P115 strain recorded faster mycelial growth compared to the HUC strain. However, both strains produced white, thick fluffy mycelial growth with radiating margin. Morphological characteristics of the mushroom fruiting body were also higher in the DMR P115 strain. The expression of these genes was analyzed using quantitative real-time PCR (qPCR) and the results were compared to those of the reference gene β-actin. The expression of laccase (POXA3) was higher in the mycelial stage of DMR P115 and HUC strains indicating its role in the fruiting body development and substrate degradation. The expression of β-glucan synthase (FKS) was upregulated in the mycelium and mature fruiting body of the DMR P115 strain. In contrast, there was only significant upregulation in the mycelial stage of the HUC strain, which indicates its role in cell wall formation and the immunostimulatory properties of that strain.

CONCLUSION

The results deepen the understanding of the molecular mechanism of the fruiting body development in P. ostreatus and can be used as a foundation for future lines of research related to strain improvement of P. ostreatus.

Current Insights in Fungal Importance-A Comprehensive Review

Besides plants and animals, the Fungi kingdom describes several species characterized by various forms and applications. They can be found in all habitats and play an essential role in the excellent functioning of the ecosystem, for example, as decomposers of plant material for the cycling of carbon and nutrients or as symbionts of plants. Furthermore, fungi have been used in many sectors for centuries, from producing food, beverages, and medications. Recently, they have gained significant recognition for protecting the environment, agriculture, and several industrial applications. The current article intends to review the beneficial roles of fungi used for a vast range of applications, such as the production of several enzymes and pigments, applications regarding food and pharmaceutical industries, the environment, and research domains, as well as the negative impacts of fungi (secondary metabolites production, etiological agents of diseases in plants, animals, and humans, as well as deteriogenic agents).

Recent Theoretical Insights into the Oxidative Degradation of Biopolymers and Plastics by Metalloenzymes

Molecular modeling techniques have become indispensable in many fields of molecular sciences in which the details related to mechanisms and reactivity need to be studied at an atomistic level. This review article provides a collection of computational modeling works on a topic of enormous interest and urgent relevance: the properties of metalloenzymes involved in the degradation and valorization of natural biopolymers and synthetic plastics on the basis of both circular biofuel production and bioremediation strategies. In particular, we will focus on lytic polysaccharide monooxygenase, laccases, and various heme peroxidases involved in the processing of polysaccharides, lignins, rubbers, and some synthetic polymers. Special attention will be dedicated to the interaction between these enzymes and their substrate studied at different levels of theory, starting from classical molecular docking and molecular dynamics techniques up to techniques based on quantum chemistry.

Impact of textile dyes on health and ecosystem: a review of structure, causes, and potential solutions

The rapid growth of population and industrialization have intensified the problem of water pollution globally. To meet the challenge of industrialization, the use of synthetic dyes in the textile industry, dyeing and printing industry, tannery and paint industry, paper and pulp industry, cosmetic and food industry, dye manufacturing industry, and pharmaceutical industry has increased exponentially. Among these industries, the textile industry is prominent for the water pollution due to the hefty consumption of water and discharge of coloring materials in the effluent. The discharge of this effluent into the aquatic reservoir affects its biochemical oxygen demand (BOD), chemical oxygen demand (COD), total dissolved solids (TDS), total suspended solids (TSS), and pH. The release of the effluents without any remedial treatment will generate a gigantic peril to the aquatic ecosystem and human health. The ecological-friendly treatment of the dye-containing wastewater to minimize the detrimental effect on human health and the environment is the need of the hour. The purpose of this review is to evaluate the catastrophic effects of textile dyes on human health and the environment. This review provides a comprehensive insight into the dyes and chemicals used in the textile industry, focusing on the typical treatment processes for their removal from industrial wastewaters, including chemical, biological, physical, and hybrid techniques.

Feasibility and potential of laccase-based enzyme in wastewater treatment through sustainable approach: A review

The worldwide increase in metropolitan cities and rise in industrialization have resulted in the assimilation of hazardous pollutants into the ecosystems. Different physical, chemical and biological techniques have been employed to remove these toxins from water bodies. Several bioprocess applications using microbes and their enzymes are utilized to achieve the goal. Biocatalysts, such as laccases, are employed explicitly to deplete a variety of organic pollutants. However, the degradation of contaminants using biocatalysts has many disadvantages concerning the stability and activity of the enzyme. Hence, they are immobilized on different supports to improve the enzyme kinetics and recyclability. Furthermore, standard wastewater treatment methods are not effective in eliminating all the contaminants. As a result, membrane separation technologies have emerged to overcome the limitations of traditional wastewater treatment methods. Moreover, enzymes immobilized onto these membranes have generated new avenues in wastewater purification technology. This review provides the latest information on laccases from diverse sources, their molecular framework and their mode of action. This report also gives information about various immobilization techniques and the application of membrane bioreactors to eliminate and biotransform hazardous contaminants. In a nutshell, laccases appear to be the most promising biocatalysts for green and cost-efficient wastewater treatment technologies.

Directed Evolution of Laccase for Improved Thermal Stability Facilitated by Droplet-Based Microfluidic Screening System

Laccases are attractive biocatalysts for industry due to their broad substrate spectrum, the use of oxygen as final electron acceptor, and water as the sole byproduct. Increasing efforts have been devoted to the engineering of laccases to improve their properties. The droplet-based microfluidic screening (DMFS) technology can accelerate the screening procedure and probe the large sequence space. In this study, a DMFS system including a heating step and picoinjection was used to sort large laccase libraries, yielding 12 variants with enhanced thermotolerance. All the obtained amino acid substitutions are distributed on the surface of the laccase. Interestingly, recombination of three identified substitutions of Asp to Asn on the surface resulted in the best variant M20, exhibiting 24.0-fold higher remaining activity at 58.8 °C and 1.9-3.4-fold higher remaining activity after incubation in organic solvents solution (20% (v/v) methanol and ethanol) and ionic liquid solution (20% (v/v) 1-ethyl-3-methylimidazolium ethyl sulfate) for 12 h. Furthermore, molecular dynamic simulations revealed that the recombination of the three beneficial substitutions, Asp98Asn, Asp474Asn, and Asp340Asn on the surface introduced more hydrogen bonds compared to the wild type, which made M20 more thermostable. This study highlighted the importance of the DMFS system for an efficient identification of beneficial long-distance amino acid substitutions.

Experimental and modeling of tetracycline degradation in water in a flow-through enzymatic monolithic reactor

In this work, the laccase from Trametes versicolor was immobilized in highly porous silica monoliths (0.6-cm diameter, 0.5-cm length). These monoliths feature a unique homogeneous network of interconnected macropores (20 μm) with mesopores (20 nm) in the skeleton and a high specific surface area (330 m²/g). The enzymatic monoliths were applied to degrade tetracycline (TC) in model aqueous solutions (20 ppm). For this purpose, a tubular flow-through reactor (FTR) configuration with recycling was built. The TC degradation was improved with oxygen saturation, presence of degradation products, and recirculation rate. The TC depletion reaches 50% in the FTR and 90% in a stirred tank reactor (CSTR) using crushed monoliths. These results indicate the importance of maintaining a high co-substrate concentration near active sites. A model coupling mass transfers with a Michaelis-Menten kinetics was applied to simulate the TC degradation in real wastewaters at actual TC concentration (2.8 10^-4 ppm). Simulation results show that industrial scale FTR reactor should be suitable to degrade 90% of TC in 5 h at a flow rate of 1 mL/min in a single passage flow configuration. Nevertheless, the process could certainly be further optimized in terms of laccase activity, oxygen supply near active sites, and contact time.

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.

Genome-wide characterization of laccase gene family in Schizophyllum commune 20R-7-F01, isolated from deep sediment 2 km below the seafloor

Laccases are ligninolytic enzymes that play a crucial role in various biological processes of filamentous fungi, including fruiting-body formation and lignin degradation. Lignin degradation is a complex process and its degradation in Schizophyllum commune is greatly affected by the availability of oxygen. Here, a total of six putative laccase genes (ScLAC) were identified from the S. commune 20R-7-F01 genome. These genes, which include three typical Cu-oxidase domains, can be classified into three groups based on phylogenetic analysis. ScLAC showed distinct intron-exon structures and conserved motifs, suggesting the conservation and diversity of ScLAC in gene structures. Additionally, the number and type of cis-acting elements, such as substrate utilization-, stress-, cell division- and transcription activation-related cis-elements, varied between ScLAC genes, suggesting that the transcription of laccase genes in S. commune 20R-7-F01 could be induced by different substrates, stresses, or other factors. The SNP analysis of resequencing data demonstrated that the ScLAC of S. commune inhabiting deep subseafloor sediments were significantly different from those of S. commune inhabiting terrestrial environments. Similarly, the large variation of conserved motifs number and arrangement of laccase between subseafloor and terrestrial strains indicated that ScLAC had a diverse structure. The expression of ScLAC5 and ScLAC6 genes was significantly up-regulated in lignin/lignite medium, suggesting that these two laccase genes might be involved in fungal utilization and degradation of lignite and lignin under anaerobic conditions. These findings might help in understanding the function of laccase in white-rot fungi and could provide a scientific basis for further exploring the relationship between the LAC family and anaerobic degradation of lignin by S. commune.

Modifying Surface Charges of a Thermophilic Laccase Toward Improving Activity and Stability in Ionic Liquid

The multicopper oxidase enzyme laccase holds great potential to be used for biological lignin valorization alongside a biocompatible ionic liquid (IL). However, the IL concentrations required for biomass pretreatment severely inhibit laccase activity. Due to their ability to function in extreme conditions, many thermophilic enzymes have found use in industrial applications. The thermophilic fungal laccase from Myceliophthora thermophila was found to retain high levels of activity in the IL [C₂C₁Im][EtSO₄], making it a desirable biocatalyst to be used for lignin valorization. In contrast to [C₂C₁Im][EtSO₄], the biocompatibility of [C₂C₁Im][OAC] with the laccase was markedly lower. Severe inhibition of laccase activity was observed in 15% [C₂C₁Im][OAc]. In this study, the enzyme surface charges were modified via acetylation, succinylation, cationization, or neutralization. However, these modifications did not show significant improvement in laccase activity or stability in [C₂C₁Im][OAc]. Docking simulations show that the IL docks close to the T1 catalytic copper, likely interfering with substrate binding. Although additional docking locations for [OAc]^- are observed after making enzyme modifications, it does not appear that these locations play a role in the inhibition of enzyme activity. The results of this study could guide future enzyme engineering efforts by showing that the inhibition mechanism of [C₂C₁Im][OAc] toward M. thermophila laccase is likely not dependent upon the IL interacting with the enzyme surface.

Pharmaceuticals in the Aquatic Environment: A Review on Eco-Toxicology and the Remediation Potential of Algae

The pollution of the aquatic environment has become a worldwide problem. The widespread use of pesticides, heavy metals and pharmaceuticals through anthropogenic activities has increased the emission of such contaminants into wastewater. Pharmaceuticals constitute a significant class of aquatic contaminants and can seriously threaten the health of non-target organisms. No strict legal regulations on the consumption and release of pharmaceuticals into water bodies have been implemented on a global scale. Different conventional wastewater treatments are not well-designed to remove emerging contaminants from wastewater with high efficiency. Therefore, particular attention has been paid to the phycoremediation technique, which seems to be a promising choice as a low-cost and environment-friendly wastewater treatment. This technique uses macro- or micro-algae for the removal or biotransformation of pollutants and is constantly being developed to cope with the issue of wastewater contamination. The aims of this review are: (i) to examine the occurrence of pharmaceuticals in water, and their toxicity on non-target organisms and to describe the inefficient conventional wastewater treatments; (ii) present cost-efficient algal-based techniques of contamination removal; (iii) to characterize types of algae cultivation systems; and (iv) to describe the challenges and advantages of phycoremediation.

Transcriptome Profiling Reveals Differential Gene Expression of Laccase Genes in Aspergillus terreus KC462061 during Biodegradation of Crude Oil

Fungal laccases have high catalytic efficiency and are utilized for the removal of crude oil because they oxidize various aliphatic and aromatic hydrocarbons and convert them into harmless compounds or less toxic compounds, thus accelerating the biodegradation potential of crude oil. Laccases are important gene families and the function of laccases genes varied widely based on transcription and function. Biodegradation of crude oil using Aspergillus terreus KC462061 was studied in the current study beside the transcription level of eight laccase (Lcc) genes have participated in biodegradation in the presence of aromatic compounds, and metal ions. Time-course profiles of laccase activity in the presence of crude oil indicated that the five inducers individual or combined have a very positive on laccase activity. In the status of the existence of crude oil, the synergistic effect of Cu-ABTS compound caused an increase in laccase yields up to 22-fold after 10 days than control. The biodegradation efficiencies of A. terreus KC462061 for aliphatic and aromatic hydrocarbons of crude oil were 82.1 ± 0.2% and 77.4 ± 0.6%, respectively. The crude oil biodegradation efficiency was improved by the supplemented Cu-ABTS compound in A. terreus KC462061. Gas chromatography-mass spectrometry was a very accurate tool to demonstrate the biodegradation efficiencies of A. terreus KC462061 for crude oil. Significant differences were observed in the SDS-PAGE of A. terreus KC462061 band intensities of laccase proteins after the addition of five inducers, but the Cu-ABTS compound highly affects very particular laccase electrophoresis. Quantitative real-time polymerase chain reaction (qPCR) was used for the analysis of transcription profile of eight laccase genes in A. terreus KC462061 with a verified reference gene. Cu²⁺ ions and Cu-ABTS were highly effective for efficient laccase expression profiling, mainly via Lcc11 and 12 transcription induction. The current study will explain the theoretical foundation for laccase transcription in A. terreus KC462061, paving the road for commercialization and usage.

Grapevine Wood-Degrading Activity of Fomitiporia mediterranea M. Fisch.: A Focus on the Enzymatic Pathway Regulation

Fomitiporia mediterranea is a Basidiomycetes fungus associated with some of the Esca complex diseases and responsible for decay in grapevine wood. Its role in the onset of foliar symptoms has recently been reconsidered, mainly after evidence showing a reduction in foliar symptom expression after removal of rotten wood. The study of its degradation pathways has already been approached by other authors, and with this study much information is consolidated. A microscopic observation of degraded wood provides a first approach to the characterization of F. mediterranea modalities of wood cellular structure degradation. The decay of grapevine wood was reproduced in vitro, and the measurement of each wood-forming polymer loss highlighted characteristics of F. mediterranea common to selective white rot and showed how fungal strain and vine variety are factors determining the wood degradation. All these observations were supported by the analysis of the laccase and manganese peroxidase enzyme activity, as well as by the expression of the genes coding 6 putative laccase isoforms and 3 manganese peroxidase isoforms, thereby highlighting substantial intraspecific variability.

Biocatalytic Elimination of Pharmaceutics Found in Water With Hierarchical Silica Monoliths in Continuous Flow

Pharmaceutical products (PPs) are considered as emerging micropollutans in wastewaters, river and seawaters, and sediments. The biodegradation of PPs, such as ciprofloxacin, amoxicillin, sulfamethoxazole, and tetracycline by enzymes in aqueous solution was investigated. Laccase from Trametes versicolor was immobilized on silica monoliths with hierarchical meso-/macropores. Different methods of enzyme immobilization were experienced. The most efficient process was the enzyme covalent bonding through glutaraldehyde coupling on amino-grafted silica monoliths. Silica monoliths with different macropore and mesopore diameters were studied. The best support was the monolith featuring the largest macropore diameter (20 µm) leading to the highest permeability and the lowest pressure drop and the largest mesopore diameter (20 nm) ensuring high enzyme accessibility. The optimized enzymatic reactor (150 mg) was used for the degradation of a PP mixture (20 ppm each in 30 ml) in a continuous recycling configuration at a flow rate of 1 ml/min. The PP elimination efficiency after 24 h was as high as 100% for amoxicillin, 60% for sulfamethoxazole, 55% for tetracycline, and 30% for ciprofloxacin.

Relationship between fruiting body development and extracellular laccase production in the edible mushroom Flammulina velutipes

The biochemical mechanism underlying the development of fruiting bodies in Flammulina velutipes, an edible mushroom, was investigated using the YBLB colorimetric assay to distinguish between the normal strain (FVN-1) and the degenerate strain (FVD-1). In this assay, the color of the YBLB medium (blue-green) inoculated with FVN-1 exhibiting normal fruiting body development changed to yellow, while the color of the medium inoculated with FVD-1 changed to blue. In this study, we found that this color difference originated from extracellular laccase produced by FVN-1. Moreover, FVN-1 exhibited considerably higher extracellular laccase activity than FVD-1, under conditions facilitating fruiting body formation. Overall, these findings suggest that extracellular laccase is involved in the fruiting body development process in F. velutipes.

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Flammulina velutipes, which forms a fruiting body, showed high laccase activity.

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A degenerate F. velutipes strain with no fruiting body showed low laccase activity.

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Extracellular laccase may contribute to fruiting body development in F. velutipes.

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Low temperature shift increased laccase activity in normal strain of F. velutipes.

Lignocellulose biomass bioconversion during composting: Mechanism of action of lignocellulase, pretreatment methods and future perspectives

Composting is a biodegradation and transformation process that converts lignocellulosic biomass into value-added products, such as humic substances (HSs). However, the recalcitrant nature of lignocellulose hinders the utilization of cellulose and hemicellulose, decreasing the bioconversion efficiency of lignocellulose. Pretreatment is an essential step to disrupt the structure of lignocellulosic biomass. Many pretreatment methods for composting may cause microbial inactivation and death. Thus, the pretreatment methods suitable for composting can promote the degradation and transformation of lignocellulosic biomass. Therefore, this review summarizes the pretreatment methods suitable for composting. Microbial consortium pretreatment, Fenton pretreatment and surfactant-assisted pretreatment for composting may improve the bioconversion process. Microbial consortium pretreatment is a cost-effective pretreatment method to enhance HSs yields during composting. On the other hand, the efficiency of enzyme production during composting is very important for the degradation of lignocellulose, whose action mechanism is unknown. Therefore, this review describes the mechanism of action of lignocellulase, the predominant microbes producing lignocellulase and their related genes. Finally, optimizing pretreatment conditions and increasing enzymatic hydrolysis to improve the quality of composts by controlling suitable microenvironmental factors and core target microbial activities as a research focus in the bioconversion of lignocellulose during composting in the future.

Laccases as green and versatile biocatalysts: from lab to enzyme market-an overview

Laccases are multi-copper oxidase enzymes that catalyze the oxidation of different compounds (phenolics and non-phenolics). The scientific literature on laccases is quite extensive, including many basic and applied research about the structure, functions, mechanism of action and a variety of biotechnological applications of these versatile enzymes. Laccases can be used in various industries/sectors, from the environmental field to the cosmetics industry, including food processing and the textile industry (dyes biodegradation and synthesis). Known as eco-friendly or green enzymes, the application of laccases in biocatalytic processes represents a promising sustainable alternative to conventional methods. Due to the advantages granted by enzyme immobilization, publications on immobilized laccases increased substantially in recent years. Many patents related to the use of laccases are available, however, the real industrial or environmental use of laccases is still challenged by cost-benefit, especially concerning the feasibility of producing this enzyme on a large scale. Although this is a compelling point and the enzyme market is heated, articles on the production and application of laccases usually neglect the economic assessment of the processes. In this review, we present a description of laccases structure and mechanisms of action including the different sources (fungi, bacteria, and plants) for laccases production and tools for laccases evolution and prediction of potential substrates. In addition, we both compare approaches for scaling-up processes with an emphasis on cost reduction and productivity and critically review several immobilization methods for laccases. Following the critical view on production and immobilization, we provide a set of applications for free and immobilized laccases based on articles published within the last five years and patents which may guide future strategies for laccase use and commercialization.

Laccase as a Tool in Building Advanced Lignin-Based Materials

Lignin is an abundant natural feedstock that offers great potential as a renewable substitute for fossil-based resources. Its polyaromatic structure and unique properties have attracted significant research efforts. The advantages of an enzymatic over chemical or thermal approach to construct or deconstruct lignins are that it operates in mild conditions, requires less energy, and usually uses non-toxic chemicals. Laccase is a widely investigated oxidative enzyme that can catalyze the polymerization and depolymerization of lignin. Its dual nature causes a challenge in controlling the overall direction of lignin-laccase catalysis. In this Review, the factors that affect laccase-catalyzed lignin polymerization were summarized, evaluated, and compared to identify key features that favor lignin polymerization. In addition, a critical assessment of the conditions that enable production of novel lignin hybrids via laccase-catalyzed grafting was presented. To assess the industrial relevance of laccase-assisted lignin valorization, patented applications were surveyed and industrial challenges and opportunities were analyzed. Finally, our perspective in realizing the full potential of laccase in building lignin-based materials for advanced applications was deduced from analysis of the limitations governing laccase-assisted lignin polymerization and grafting.

Removal of Aflatoxin B1 by Edible Mushroom-Forming Fungi and Its Mechanism

Aflatoxins (AFs) are biologically active toxic metabolites, which are produced by certain toxigenic Aspergillus sp. on agricultural crops. In this study, five edible mushroom-forming fungi were analyzed using high-performance liquid chromatography fluorescence detector (HPLC-FLD) for their ability to remove aflatoxin B₁ (AFB₁), one of the most potent naturally occurring carcinogens known. Bjerkandera adusta and Auricularia auricular-judae showed the most significant AFB₁ removal activities (96.3% and 100%, respectively) among five strains after 14-day incubation. The cell lysate from B. adusta exhibited higher AFB₁ removal activity (35%) than the cell-free supernatant (13%) after 1-day incubation and the highest removal activity (80%) after 5-day incubation at 40 °C. In addition, AFB₁ analyses using whole cells, cell lysates, and cell debris from B. adusta showed that cell debris had the highest AFB₁ removal activity at 5th day (95%). Moreover, exopolysaccharides from B. adusta showed an increasing trend (24–48%) similar to whole cells and cell lysates after 5- day incubation. Our results strongly suggest that AFB₁ removal activity by whole cells was mainly due to AFB₁ binding onto cell debris during early incubation and partly due to binding onto cell lysates along with exopolysaccharides after saturation of AFB₁ binding process onto cell wall components.

Review of advances in the development of laccases for the valorization of lignin to enable the production of lignocellulosic biofuels and bioproducts

Development and deployment of commercial biorefineries based on conversion of lignocellulosic biomass into biofuels and bioproducts faces many challenges that must be addressed before they are commercially viable. One of the biggest challenges faced is the efficient and scalable valorization of lignin, one of the three major components of the plant cell wall. Lignin is the most abundant aromatic biopolymer on earth, and its presence hinders the extraction of cellulose and hemicellulose that is essential to biochemical conversion of lignocellulose to fuels and chemicals. There has been a significant amount of work over the past 20 years that has sought to develop innovative processes designed to extract and recycle lignin into valuable compounds and help reduce the overall costs of the biorefinery process. Due to the complex matrix of lignin, which is essential for plant survival, the development of a reliable and efficient lignin conversion technology has been difficult to achieve. One approach that has received significant interest relies on the use of enzymes, notably laccases, a class of multi‑copper green oxidative enzymes that catalyze bond breaking in lignin to produce smaller oligomers. In this review, we first assess the different innovations of lignin valorization using laccases within the context of a biorefinery process, and then assess the latest economical advances that these innovations offered. Finally, we review laccase characterization and optimization, as well as the prospects and bottlenecks of this class of enzymes within the industrial and biorefining sectors.

Molecular self-organization of wood lignin-carbohydrate matrix

The analysis of the state of research on the chemical composition, functional nature and structure of the main components of the lignin-carbohydrate matrix allows considering the wood substance as a thermodynamically self-organizing nanobiocomposite system. Features of biosynthesis of the wood matrix main biopolymers, the formation of their functional nature and structure determine the complex hierarchical organization of cell walls. The supramolecular level of biosynthesis considers the interaction of cell wall components. On the one hand, these are questions of dynamics of cell walls synthesis and processes of self-organization that control the formation of chaotic objects of biological origin; on the other hand, it is the question of thermodynamic compatibility of plant tissue components. Various models of structural organization are currently being considered, focusing on various features (biological, chemical, structural) of wood substance. At the same time, the lignin-carbohydrate matrix is a three-component system of natural polymers: lignin-hemicelluloses-cellulose, the state of which is described by specific values of thermodynamic parameters that characterize the degree of its stability. The new approach proposed in this paper allows considering the plant lignin-carbohydrate matrix from the standpoint of physical chemistry of polymer as quasi-equilibrium, thermodynamically limited ordered system of biopolymers. Thus, the biochemical processes of synthesis and self-organization lead to the formation of a complex multicomponent system of wood substance, considered as a nanobiocomposite. This determines the need to study the applicability of the fundamental cycle "structure-functional nature-properties" from the standpoint of physical chemistry of biopolymers both for the investigation of plant objects and for the development of modern technologies for complex processing based on the principles of "green chemistry".

Biochemical Characterization of a Novel Bacterial Laccase and Improvement of Its Efficiency by Directed Evolution on Dye Degradation

Laccase is a copper-containing polyphenol oxidase with a wide range of substrates, possessing a good application prospect in wastewater treatment and dye degradation. The purpose of this research is to study the degradation of various industrial dyes by recombinant laccase rlac1338 and the mutant enzyme lac2-9 with the highest enzyme activity after modification by error-prone PCR. Four enzyme activities improved mutant enzymes were obtained through preliminary screening and rescreening, of which lac2-9 has the highest enzyme activity. There are four mutation sites, including V281A, V281A, P309L, S318G, and D232V. The results showed that the expression of the optimized mutant enzyme also increased by 22 ± 2% compared to the unoptimized enzyme and the optimal reaction temperature of the mutant enzyme lac2-9 was 5°C higher than that of the rlac1338, and the optimal pH increased by 0.5 units. The thermal stability and pH stability of mutant enzyme lac2-9 were also improved. With ABTS as the substrate, the k_cat/K_m of rlac1338 and mutant strain lac2-9 are the largest than other substrates, 0.1638 and 0.618 s^–1M^–1, respectively, indicating that ABTS is the most suitable substrate for the recombinant enzyme and mutant enzyme. In addition, the K_m of the mutant strain lac2-9 (76 μM) was significantly lower, but the k_cat/K_m (0.618 s^–1M^–1) was significantly higher, and the specific enzyme activity (79.8 U/mg) increased by 3.5 times compared with the recombinant laccase (22.8 U/mg). The dye degradation results showed that the use of rlac1338 and lac2-9 alone had no degradation effect on the industrial dyes [indigo, amaranth, bromophenol blue, acid violet 7, Congo red, coomassie brilliant blue (G250)], however, adding small molecular mediators Ca²⁺ and ABTS at the same time can significantly improve the degradation ability. Compared to the rlac1338, the degradation rates with the simultaneous addition of Ca²⁺ and ABTS of mutant enzyme lac2-9 for acid violet 7, bromophenol blue and coomassie brilliant blue significantly improved by 8.3; 3.4 and 3.4 times. Therefore, the results indicated that the error-prone PCR was a feasible method to improve the degradation activity of laccase for environmental pollutants, which provided a basis for the application of laccase on dye degradation and other environmental pollutants.

Rational engineering of the lccβ T. versicolor laccase for the mediator-less oxidation of large polycyclic aromatic hydrocarbons

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Computational-assisted protein engineering of the binding pocket of laccases.

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Mutants have activity increased up to ~ 300% in a broader pH range compared to the WT.

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Enhanced activity towards bulky PAHs in comparison to the WT enzyme.

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Ability to oxidize harmful PAH model compounds (dyes) that the WT enzyme cannot modify.

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Higher oxidation levels without mediators compared to the WT laccase with mediators.

Laccases are among the most sought-after biocatalyst for many green applications, from biosensors to pollution remedial, because they simply need oxygen from the air to oxidize and degrade a broad range of substrates. However, natural laccases cannot process large and toxic polycyclic aromatic hydrocarbons (PAHs) except in the presence of small molecules, called mediators, which facilitate the reaction but are inconvenient for practical on-field applications. Here we exploited structure-based protein engineering to generate rationally modified fungal laccases with increased ability to process bulky PAHs even in a mediator-less reaction. Computational simulations were used to estimate the impact of mutations in the enzymatic binding pocket on the ability to bind and oxidize a selected set of organic compounds. The most promising mutants were produced and their activity was evaluated by biochemical assays with phenolic and non-phenolic substrates. Mutant laccases engineered with a larger binding pocket showed enhanced activity (up to ~ 300% at pH 3.0) in a wider range of pH values (3.0–8.0) in comparison to the wild type enzyme. In contrast to the natural laccase, these mutants efficiently degraded bulky and harmful triphenylmethane dyes such as Ethyl Green (up to 91.64% after 24 h), even in the absence of mediators, with positive implications for the use of such modified laccases in many green chemistry processes (e.g. wastewater treatment).

Cloning, Overexpression, and Characterization of a Thermostable, Organic Solvent-Tolerant Laccase from Bacillus pumilus ARA and Its Application to Dye Decolorization

A thermostable and organic solvent-tolerant bacterial laccase from Bacillus pumilus ARA has been expressed heterologously and characterized, which shows potential decolorization capacity to various types of industrial synthetic dyes. The optimal temperature and pH were 85 °C and 3.5, respectively, while the purified recombinant laccase B.P.Lacc was stable under 55-75 °C and pH 5.0-8.0 conditions. The apparent kinetic parameters K m and V max of B.P.Lacc for ABTS as the substrate were 0.33 mM and 32.4 U/mg, respectively. Ethanol (1%, v/v) and methanol (2%, v/v) could stimulate the enzyme activity. The recombinant laccase retained over 95% of its initial activity in 10% (v/v) methanol. The optimal expression conditions for the laccase production of B.P.Lacc in LB medium were obtained: induction temperature of 25 °C, 0.4 mM Cu2+, and 1.0 mM IPTG added into the culture. After 5 h, the final laccase production was 1283 U/mL. Moreover, the laccase activity increased to 4822 U/mL after follow-up 2 h stationary cultivation, with about a 3.76-fold increase. The purified B.P.Lacc was able to efficiently decolorize synthetic dyes combined with mediators. Adding 1.0 mM ABTS, more than 90% of BRRB was decolorized by the enzyme, whether at pH 4.0 or pH 7.9. The outstanding enzymatic properties suggested that B.P.Lacc may be suitable for a wide application in future biodegradation fields.

Phytocatalytic and cytotoxic activity of the purified laccase from bled resin of Pistacia atlantica Desf

This study reports an efficient and fast procedure for the purification of laccase (PaL) obtained from the resin of Pistacia atlantica Desf. It was purified by one-step affinity chromatography and showed the specific activity of 393 U/mg with 81.9-fold purification. The molecular weight of PaL was estimated to be approximately 60 kDa using gel electrophoresis SDS-PAGE. Moreover, it depicted diphenolase activity and high affinity towards 2,6-dimethoxy phenol (K_m = 10.01 ± 0.5 mM) and syringaldazine (K_m = 6.57 ± 0.2 mM) comparing with plant-origin polyphenol oxidases reported in the literature. It should be noted that PaL possessed optimal activity at pH 7.5 and 45 °C. It also remained stable under different conditions of pH (6.5-8.0), temperature (25-45 °C), and when it was exposed to several metal ions. The MTT and flow cytometry assays demonstrated that the enzyme treatment significantly affected growth of HeLa, HepG2, and MDA-MB-231 cells with LC₅₀ values of 4.83 ± 0.02, 61 ± 0.31, and 26.83 ± 0.11 μM after 72 h, respectively. NOVELTY STATEMENT: This is the first attempt to isolate and characterize a new oxidoreductase from the resin of Pistacia atlantica Desf., native species of Iran, to recruit it in cytotoxicity researches. In the purification process by an efficient affinity column (SBA-NH₂-GA), the enzyme was eluted promptly with a satisfied yield. The purified laccase exerted higher affinity to diphenolic compounds and pH-thermal stability compared to other plant-derived polyphenol oxidases. The purified enzyme was found to show anti-oxidant capacity and significantly inhibited the growth of cancerous cells in vitro. PaL showed more cytotoxic activity towards HeLa and MDA-MB-231 cells by induction of apoptosis. The cytotoxic activity of the laccase was measured by flow cytometry.

Application of laccases for mycotoxin decontamination

Several food commodities can be infected by filamentous fungi, both in the field and during storage. Some of these fungi, under appropriate conditions, are capable of producing a wide range of secondary metabolites, including mycotoxins, which may resist food processing and arise in the final feed and food products. Contamination of these products with mycotoxins still occurs very often and that is why research in this area is valuable and still evolving. The best way to avoid contamination is prevention; however, when it is not possible, remediation is the solution. Enzymatic biodegradation of mycotoxins is a green solution for removal of these compounds that has attracted growing interest over recent years. Due to their ability to detoxify a wide variety of recalcitrant pollutants, laccases have received a lot of attention. Laccases are multi-copper proteins that use molecular oxygen to oxidise various aromatic and non-aromatic compounds, by a radical-catalysed reaction mechanism. Being non-specific, they are capable of degrading a wide range of compounds and the radical species formed can evolve towards both synthetic and degradative processes. The present review provides an overview of structural features, biological functions and catalytic mechanisms of laccases. The utilisation of laccases for mycotoxin degradation is reviewed, as well as shortcomings and future needs related with the use of laccases for mycotoxin decontamination from food and feed.

Genome-based engineering of ligninolytic enzymes in fungi

Background

Many fungi grow as saprobic organisms and obtain nutrients from a wide range of dead organic materials. Among saprobes, fungal species that grow on wood or in polluted environments have evolved prolific mechanisms for the production of degrading compounds, such as ligninolytic enzymes. These enzymes include arrays of intense redox-potential oxidoreductase, such as laccase, catalase, and peroxidases. The ability to produce ligninolytic enzymes makes a variety of fungal species suitable for application in many industries, including the production of biofuels and antibiotics, bioremediation, and biomedical application as biosensors. However, fungal ligninolytic enzymes are produced naturally in small quantities that may not meet the industrial or market demands. Over the last decade, combined synthetic biology and computational designs have yielded significant results in enhancing the synthesis of natural compounds in fungi.

Main body of the abstract

In this review, we gave insights into different protein engineering methods, including rational, semi-rational, and directed evolution approaches that have been employed to enhance the production of some important ligninolytic enzymes in fungi. We described the role of metabolic pathway engineering to optimize the synthesis of chemical compounds of interest in various fields. We highlighted synthetic biology novel techniques for biosynthetic gene cluster (BGC) activation in fungo and heterologous reconstruction of BGC in microbial cells. We also discussed in detail some recombinant ligninolytic enzymes that have been successfully enhanced and expressed in different heterologous hosts. Finally, we described recent advance in CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats)-Cas (CRISPR associated) protein systems as the most promising biotechnology for large-scale production of ligninolytic enzymes.

Short conclusion

Aggregation, expression, and regulation of ligninolytic enzymes in fungi require very complex procedures with many interfering factors. Synthetic and computational biology strategies, as explained in this review, are powerful tools that can be combined to solve these puzzles. These integrated strategies can lead to the production of enzymes with special abilities, such as wide substrate specifications, thermo-stability, tolerance to long time storage, and stability in different substrate conditions, such as pH and nutrients.

Genes Identification, Molecular Docking and Dynamics Simulation Analysis of Laccases from Amylostereum areolatum Provides Molecular Basis of Laccase Bound to Lignin

An obligate mutualistic relationship exists between the fungus Amylostereum areolatum and woodwasp Sirex noctilio. The fungus digests lignin in the host pine, providing essential nutrients for the growing woodwasp larvae. However, the functional properties of this symbiosis are poorly described. In this study, we identified, cloned, and characterized 14 laccase genes from A. areolatum. These genes encoded proteins of 508 to 529 amino acids and contained three typical copper-oxidase domains, necessary to confer laccase activity. Besides, we performed molecular docking and dynamics simulation of the laccase proteins in complex with lignin compounds (monomers, dimers, trimers, and tetramers). AaLac2, AaLac3, AaLac6, AaLac8, and AaLac10 were found that had low binding energies with all lignin model compounds tested and three of them could maintain stability when binding to these compounds. Among these complexes, amino acid residues ALA, GLN, LEU, PHE, PRO, and SER were commonly present. Our study reveals the molecular basis of A. areolatum laccases interacting with lignin, which is essential for understanding how the fungus provides nutrients to S. noctilio. These findings might also provide guidance for the control of S. noctilio by informing the design of enzyme mutants that could reduce the efficiency of lignin degradation.

Enzyme Properties of a Laccase Obtained from the Transcriptome of the Marine-Derived Fungus Stemphylium lucomagnoense

Only a few studies have examined how marine-derived fungi and their enzymes adapt to salinity and plant biomass degradation. This work concerns the production and characterisation of an oxidative enzyme identified from the transcriptome of marine-derived fungus Stemphylium lucomagnoense. The laccase-encoding gene SlLac2 from S. lucomagnoense was cloned for heterologous expression in Aspergillus niger D15#26 for protein production in the extracellular medium of around 30 mg L⁻¹. The extracellular recombinant enzyme SlLac2 was successfully produced and purified in three steps protocol: ultrafiltration, anion-exchange chromatography, and size exclusion chromatography, with a final recovery yield of 24%. SlLac2 was characterised by physicochemical properties, kinetic parameters, and ability to oxidise diverse phenolic substrates. We also studied its activity in the presence and absence of sea salt. The molecular mass of SlLac2 was about 75 kDa, consistent with that of most ascomycete fungal laccases. With syringaldazine as substrate, SlLac2 showed an optimal activity at pH 6 and retained nearly 100% of its activity when incubated at 50°C for 180 min. SlLac2 exhibited more than 50% of its activity with 5% wt/vol of sea salt.

A highly thermotolerant laccase produced by Cerrena unicolor strain CGMCC 5.1011 for complete and stable malachite green decolorization

Laccases are a class of multi-copper oxidases with important industrial values. A thermotolerant laccase produced by a basidiomycete fungal strain Cerrena unicolor CGMCC 5.1011 was studied. With glycerin and peptone as the carbon and nitrogen sources, respectively, a maximal laccase activity of 121.7 U/mL was attained after cultivation in the shaking flask for 15 days. Transcriptomics analysis revealed an expressed laccase gene family of 12 members in C. unicolor strain CGMCC 5.1011, and the gene and cDNA sequences were cloned. A glycosylated laccase was purified from the fermentation broth of Cerrena unicolor CGMCC 5.1011 and corresponded to Lac2 based on MALDI-TOF MS/MS identification. Lac2 was stable at pH 5.0 and above, and was resistant to organic solvents. Lac2 displayed remarkable thermostability, with half-life time of 1.67 h at 70 ºC. Consistently, Lac2 was able to completely decolorize malachite green (MG) at high temperatures, whereas Lac7 from Cerrena sp. HYB07 resulted in accumulation of colored MG transformation intermediates. Molecular dynamics simulation of Lac2 was conducted, and possible mechanisms underlying Lac2 thermostability were discussed. The robustness of C. unicolor CGMCC 5.1011 laccase would not only be useful for industrial applications, but also provide a template for future work to develop thermostable laccases.

New strategy for grafting hydrophobization of lignocellulosic fiber materials with octadecylamine using a laccase/TEMPO system

The enzymatic functionalization of lignocellulosic fibers using oxidoreductases was successfully achieved by targeting lignin moieties as grafting sites on the surface. In this study, a novel strategy for hydrophobization of lignocelluloses was investigated, which involved the laccase/TEMPO-mediated grafting of octadecylamine (OA) onto both lignin and cellulose components of jute fabrics. The results showed that OA monomers were successfully grafted onto jute fabric surface using the laccase/TEMPO system with the grafting percentage and efficiency values of 0.712% and 10.571%, respectively. The primary hydroxyl groups of cellulose were oxidized by laccase/TEMPO to carbonyl groups, which were then coupled with amino-contained OA monomers via Schiff base reaction. The phenolic hydroxyl groups of lignin were transformed by laccase to radicals, on which OA molecules were grafted via Michael addition reaction. Consequently, grafted jute fabrics showed a considerable increase in the surface hydrophobicity with a contact angle of 125.9° and a wetting time of at least 2 h. Furthermore, there was an acceptable decrease in the breaking strength of jute fabrics by 13.60%, and the color of fabrics turned yellowish and reddish. This eco-friendly enzymatic process provides a new strategy for grafting hydrophobization and even functionalization of lignocellulosic fiber materials using amino compounds.

High-potency white-rot fungal strains and duration of fermentation to optimize corn straw as ruminant feed

Five white-rot fungi Pleurotus ostreatus, Lentinus edodes, Hericium erinaceus, Pleurotus eryngii and Flammulina filiformis were studied (solid-state incubation and in vitro gas production) to determine lignin degradation and optimal duration of fermentation of corn straw. All fungi significantly decreased lignin, with optimal reductions after 28 d. Although cellulose also decreased, L. edodes and P. eryngii minimized these losses. In intro dry matter digestibility, total volatile fatty acid concentration and total gas production of fermented corn straw decreased (P < 0.001) as fermentation was prolonged, with improved rumen fermentability for all fungal treatments except F. filiformis. Total gas production in L. edodes did not decrease but peaked on day 28, whereas F. filiformis reduced methane emission. In conclusion, fermentation of corn straw with P. eryngii or L. edodes for 28 d degraded lignin and improved nutritional value as ruminant feed.

Multiple Tolerance and Dye Decolorization Ability of a Novel Laccase Identified from Staphylococcus Haemolyticus

Laccases are multicopper oxidases with important industrial value. In the study, a novel laccase gene (mco) in a Staphylococcus haemolyticus isolate is identified and heterologously expressed in Escherichia coli. Mco shares less than 40% of amino acid sequence identities with the other characterized laccases, exhibiting the maximal activity at pH 4.0 and 60°C with 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid) diammonium salt (ABTS) as a substrate. Additionally, the Mco is tolerant to a wide range of pH, heavy metal ions and many organic solvents, and it has a high decolorization capability toward textile dyes in the absence of redox mediators. The characteristics of the Mco make this laccase potentially useful for industrial applications such as textile finishing. Based on BLASTN results, mco is found to be widely distributed in both the bacterial genome and bacterial plasmids. Its potential role in oxidative defense ability of staphylococci may contribute to the bacterial colonization and survival.

Model Compounds Study for the Mechanism of Horseradish Peroxidase-Catalyzed Lignin Modification

Horseradish peroxidase (HRP) has demonstrated high activity for the modification of lignin. In this paper, several lignin model compounds with different functional groups and linkages are selected to investigate the reactivity of HRP-catalyzed lignin modification. The phenolic groups of lignin model compounds are indispensable for the HRP-catalyzed modification process. The introduction of the sulfomethylated methyl group or methoxyl group could facilitate or inhibit the modification, respectively. The oxidative coupling activity of α-O-4 lignin model compounds is higher than that of β-O-4 compounds. Meanwhile, the free energy obtained by density functional theory (DFT) is used to verify the results of the experimental study, and the order of preference for linkages is β-5 > β-β > β-O-4 in most cases. In addition, electron cloud density and steric hindrance of lignin model compounds have crucial effects on the oxidation and modification processes. Finally, the mechanism of HRP-catalyzed lignin modification is proposed.

Degradation of Aflatoxin B1 by a Sustainable Enzymatic Extract from Spent Mushroom Substrate of Pleurotus eryngii

Ligninolytic enzymes from white-rot fungi, such as laccase (Lac) and Mn-peroxidase (MnP), are able to degrade aflatoxin B₁ (AFB1), the most harmful among the known mycotoxins. The high cost of purification of these enzymes has limited their implementation into practical technologies. Every year, tons of spent mushroom substrate (SMS) are produced as a by-product of edible mushroom cultivation, such as Pleurotus spp., and disposed at a cost for farmers. SMS may still bea source of ligninolytic enzymes useful for AFB1 degradation. The in vitro AFB1-degradative activity of an SMS crude extract (SMSE) was investigated. Results show that: (1) in SMSE, high Lac activity (4 U g⁻¹ dry matter) and low MnP activity (0.4 U g⁻¹ dry matter) were present; (2) after 1 d of incubation at 25 °C, the SMSE was able to degrade more than 50% of AFB1, whereas after 3 and 7 d of incubation, the percentage of degradation reached the values of 75% and 90%, respectively; (3) with increasing pH values, the degradation percentage increased, reaching 90% after 3 d at pH 8. Based on these results, SMS proved to be a suitable source of AFB1 degrading enzymes and the use of SMSE to detoxify AFB1 contaminated commodities appears conceivable.

TiO2 Sol-Gel Coated PAN/O-MMT Multi-Functional Composite Nanofibrous Membrane Used as the Support for Laccase Immobilization: Synergistic Effect between the Membrane Support and Enzyme for Dye Degradation

Removal of a triphenylmethane dye (crystal violet, CV) by a simultaneous enzymatic-photocatalytic-adsorption treatment was investigated in this work. A desirable synergistic effect on dye treatment was achieved by decorating laccase (Lac) onto the surface of TiO₂ sol-gel coated polyacrylonitrile/organically modified montmorillonite (PAN/O-MMT) nanofibers prepared by electrospinning. The assembly of Lac on the surface of PAN/O-MMT/TiO₂ nanofibers was confirmed by confocal laser scanning microscope (CLSM). In comparison with free Lac, the immobilized Lac showed better pH, temperature and operational stabilities, reaching highest relative activity at an optimum pH of 3 and optimum temperature of 50 °C. Therefore, the immobilized Lac displayed a higher degradation efficiency of CV at an initial dye concentration of 100 mg/L, an optimum pH of 4.5 and temperature at 60 °C. Under UV illumination, the CV removal efficiency was further improved by ~20%. These results demonstrated that the Lac-immobilized PAN/O-MMT/TiO₂ composite nanofibers with a combined effect between the immobilized enzyme and the polymeric support have potential for industrial dye degradation.