Recombinant expression of Pleurotus ostreatus laccases in Kluyveromyces lactis and Saccharomyces cerevisiae

Simultaneous enhancement of activity and stability of Bacillus safensis-derived laccase and its application in lignocellulose saccharification

Effective hydrolysis of lignocelluloses for producing reducing sugar is impeded by the covalent binding of hemicellulose and cellulose through lignin, which could be eliminated by laccases. This study identified a novel thermostable laccase from Bacillus safensis TCCC 111022 and created an iterative mutant E231D/Y441H, exhibiting 1.59-fold greater specific activity and a 183 % greater half-life at 80°C than the wild-type enzyme. Computational analysis revealed that the stability and activity of the E231D/Y441H could be simultaneously enhanced by increasing the flexibility of the ring around the substrate binding pocket. Additionally, the saccharification efficiency of sugarcane bagasse and corn stalks were both enhanced by 235 % in the system adding E231D/Y441H, mixed-cellulases, and mediator (1-hydroxybenzotriazole) compared to the samples treated with mixed-cellulases. The findings of this research provide a reference for the degradation of lignocellulosic substrates and contribute to the sustainable development of biomass-based industries.

Is Laccase derived from Pleurotus ostreatus effective in microplastic degradation? A critical review of current progress, challenges, and future prospects

Exploration of Pleurotus ostreatus as a biological agent in the degradation of persistent plastics like polyethylene, polystyrene, polyvinyl chloride, and polyethylene terephthalate, revealing a promising avenue toward mitigating the environmental impacts of plastic pollution. Leveraging the intrinsic enzymatic capabilities of this fungus, mainly its production of laccase, presents a sustainable and eco-friendly approach to breaking down complex polymer chains into less harmful constituents. This review focused on enhancements in the strain's efficiency through genetic engineering, optimized culture conditions, and enzyme immobilization to underscore the potential for scalability and practical application of this bioremediation process. The utilization of laccase from P. ostreatus in plastic waste management demonstrates a vital step forward in pursuing sustainable environmental solutions. By using the potential of fungal bioremediation, researchers can move closer to a future in which the adverse effects of plastic pollution are significantly mitigated, benefiting the health of our planet and future generations.

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

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

Spectrophotometric Assay for the Detection of 2,5-Diformylfuran and Its Validation through Laccase-Mediated Oxidation of 5-Hydroxymethylfurfural

Modern biocatalysis requires fast, sensitive, and efficient high-throughput screening methods to screen enzyme libraries in order to seek out novel biocatalysts or enhanced variants for the production of chemicals. For instance, the synthesis of bio-based furan compounds like 2,5-diformylfuran (DFF) from 5-hydroxymethylfurfural (HMF) via aerobic oxidation is a crucial process in industrial chemistry. Laccases, known for their mild operating conditions, independence from cofactors, and versatility with various substrates, thanks to the use of chemical mediators, are appealing candidates for catalyzing HMF oxidation. Herein, Schiff-based polymers based on the coupling of DFF and 1,4-phenylenediamine (PPD) have been used in the set-up of a novel colorimetric assay for detecting the presence of DFF in different reaction mixtures. This method may be employed for the fast screening of enzymes (Z' values ranging from 0.68 to 0.72). The sensitivity of the method has been proved, and detection (8.4 μM) and quantification (25.5 μM) limits have been calculated. Notably, the assay displayed selectivity for DFF and enabled the measurement of kinetics in DFF production from HMF using three distinct laccase-mediator systems.

Statistical Improvement of rGILCC 1 and rPOXA 1B Laccases Activity Assay Conditions Supported by Molecular Dynamics

Laccases (E.C. 1.10.3.2) are glycoproteins widely distributed in nature. Their structural conformation includes three copper sites in their catalytic center, which are responsible for facilitating substrate oxidation, leading to the generation of H2O instead of H2O2. The measurement of laccase activity (UL-1) results may vary depending on the type of laccase, buffer, redox mediators, and substrates employed. The aim was to select the best conditions for rGILCC 1 and rPOXA 1B laccases activity assay. After sequential statistical assays, the molecular dynamics proved to support this process, and we aimed to accumulate valuable insights into the potential application of these enzymes for the degradation of novel substrates with negative environmental implications. Citrate buffer treatment T2 (CB T2) (pH 3.0 ± 0.2; λ420nm, 2 mM ABTS) had the most favorable results, with 7.315 ± 0.131 UL-1 for rGILCC 1 and 5291.665 ± 45.83 UL-1 for rPOXA 1B. The use of citrate buffer increased the enzyme affinity for ABTS since lower Km values occurred for both enzymes (1.49 × 10-2 mM for rGILCC 1 and 3.72 × 10-2 mM for rPOXA 1B) compared to those obtained in acetate buffer (5.36 × 10-2 mM for rGILCC 1 and 1.72 mM for rPOXA 1B). The molecular dynamics of GILCC 1-ABTS and POXA 1B-ABTS showed stable behavior, with root mean square deviation (RMSD) values not exceeding 2.0 Å. Enzyme activities (rGILCC 1 and rPOXA 1B) and 3D model-ABTS interactions (GILCC 1-ABTS and POXA 1B-ABTS) were under the strong influence of pH, wavelength, ions, and ABTS concentration, supported by computational studies identifying the stabilizing residues and interactions. Integration of the experimental and computational approaches yielded a comprehensive understanding of enzyme-substrate interactions, offering potential applications in environmental substrate treatments.

The phenomenon of strain degeneration in biotechnologically relevant fungi

Fungi are widely exploited for large-scale production in the biotechnological industry to produce a diverse range of substances due to their versatility and relative ease of growing on various substrates. The occurrence of a phenomenon-the so-called fungal strain degeneration-leads to the spontaneous loss or decline of production capacity and results in an economic loss on a tremendous scale. Some of the most commonly applied genera of fungi in the biotechnical industry, such as Aspergillus, Trichoderma, and Penicillium, are threatened by this phenomenon. Although fungal degeneration has been known for almost a century, the phenomenon and its underlying mechanisms still need to be understood. The proposed mechanisms causing fungi to degenerate can be of genetic or epigenetic origin. Other factors, such as culture conditions, stress, or aging, were also reported to have an influence. This mini-review addresses the topic of fungal degeneration by describing examples of productivity losses in biotechnical processes using Aspergillus niger, Aspergillus oryzae, Trichoderma reesei, and Penicillium chrysogenum. Further, potential reasons, circumvention, and prevention methods are discussed. This is the first mini-review which provides a comprehensive overview on this phenomenon in biotechnologically used fungi, and it also includes a collection of strategies that can be useful to minimize economic losses which can arise from strain degeneration. KEY POINTS: • Spontaneous loss of productivity is evident in many fungi used in biotechnology. • The properties and mechanisms underlying this phenomenon are very versatile. • Only studying these underlying mechanisms enables the design of a tailored solution.

Mycoremediation with Agaricus bisporus and Pleurotus ostreatus growth substrates versus phytoremediation with Festuca rubra and Brassica sp. for the recovery of a Pb and γ-HCH contaminated soil

Mycoremediation with mushroom growth substrates can be used for the recovery of mixed contaminated soils due to the benefits derived from the physicochemical characteristics of the substrates, the activity of extracellular enzymes secreted by the fungi, and the presence of the fungal mycelia. The objective of this work was to assess the potential of Agaricus bisporus and Pleurotus ostreatus growth substrates (inoculated mushroom substrates vs. spent mushroom substrates) for the mycoremediation of soils co-contaminated with lead and lindane (γ-HCH). We compared the efficiency of these mycoremediation strategies with the phytoremediation with Brassica spp. Or Festuca rubra plants, in terms of both reduction in contaminant levels and enhancement of soil health. An enhanced soil health was achieved as a result of the application of mycoremediation treatments, compared to phytoremediation and control (untreated) treatments. The application of P. ostreatus inoculated substrate led to the most significant reduction in γ-HCH concentration (up to 88.9% compared to corresponding controls). In the presence of inoculated mushroom substrate, P. ostreatus fruiting bodies extracted more Pb than Brassica spp. Or F. rubra plants. Mycoremediation with P. ostreatus growth substrates appears a promising strategy for the recovery of the health of soils co-contaminated with Pb and γ-HCH.

Valorization of Lignin and Its Derivatives Using Yeast

As the third most plentiful biopolymer after other lignocellulosic derivates such as cellulose and hemicellulose, lignin carries abundant potential as a substitute for petroleum-based products. However, the efficient, practical, value-added product valorization of lignin remains quite challenging. Although several studies have reviewed the valorization of lignin by microorganisms, this present review covers recent studies on the valorization of lignin by employing yeast to obtain products such as single-cell oils (SCOs), enzymes, and other chemical compounds. The use of yeasts has been found to be suitable for the biological conversion of lignin and might provide new insights for future research to develop a yeast strain for lignin to produce other valuable chemical compounds.

Mushroom Ligninolytic Enzymes―Features and Application of Potential Enzymes for Conversion of Lignin into Bio-Based Chemicals and Materials

Mushroom ligninolytic enzymes are attractive biocatalysts that can degrade lignin through oxido-reduction. Laccase, lignin peroxidase, manganese peroxidase, and versatile peroxidase are the main enzymes that depolymerize highly complex lignin structures containing aromatic or aliphatic moieties and oxidize the subunits of monolignol associated with oxidizing agents. Among these enzymes, mushroom laccases are secreted glycoproteins, belonging to a polyphenol oxidase family, which have a powerful oxidizing capability that catalyzes the modification of lignin using synthetic or natural mediators by radical mechanisms via lignin bond cleavage. The high redox potential laccase within mediators can catalyze the oxidation of a wide range of substrates and the polymerization of lignin derivatives for value-added chemicals and materials. The chemoenzymatic process using mushroom laccases has been applied effectively for lignin utilization and the degradation of recalcitrant chemicals as an eco-friendly technology. Laccase-mediated grafting has also been employed to modify lignin and other polymers to obtain novel functional groups able to conjugate small and macro-biomolecules. In this review, the biochemical features of mushroom ligninolytic enzymes and their potential applications in catalytic reactions involving lignin and its derivatives to obtain value-added chemicals and novel materials in lignin valorization are discussed.

Tertiary treatment (Chlorella sp.) of a mixed effluent from two secondary treatments (immobilized recombinant P. pastori and rPOXA 1B concentrate) of coloured laboratory wastewater (CLWW)

Industrial development has increased wastewater (WW) volume; generating contamination and disturbing ecosystems, because of breeching disposal parameters. In this work, Coloured Laboratory Wastewater (CLWW), (1500.00 colour units, CU) was separately submitted to two secondary treatments. For the first one CLWW was treated for three cycles C1, C2 and C3 with P. pastoris X33/pGAPZαA-LaccPost-Stop producing rPOXA 1B laccase, immobilized in calcium alginate beads. For the second-one, rPOXA 1B enzyme concentrate was used (three processes: P1, P2, and P3). Both treatments were carried out in a 15 L reactor with 10 L effective work volume (EWV) with 72 h hydraulic retention time. C1, C2, and C3 effluents were flocculated and filtered through quartzite sand, while P1, P2, and P3 effluents were only filtered through quartzite sand. The mixture of secondary effluents was submitted to a tertiary treatment with Chlorella sp. For C1, C2, C3, P1, P2, and P3, CU removal was of 99.16, 99.58, 99.53, 96.72, 97.05 and 96.47%, respectively. Discharge parameters, total organic carbon (TOC), inorganic carbon (IC), chemical oxygen demand (COD) and biological oxygen demand (BOD₅) decreased, although they reached different final values. After the tertiary treatment (144 h) effluent discharge parameters were reduced to 34 ± 4 CU, TOC to 6.6 ± 0.9 mg L^-1 and COD to 155 ± 4 mg L^-1. It was demonstrated that secondary treatments (immobilized recombined cells or recombinant enzyme concentrate) combined with Chlorella sp., (tertiary treatment) attained a considerable removal of discharge parameters, demonstrating a promissory alternative for CLWW sequential treatment.

Identification of oleaginous yeasts that metabolize aromatic compounds

The valorization of lignin is critical for the economic viability of the bioeconomy. Microbial metabolism is advantageous for handling the myriad of aromatic compounds resulting from lignin chemical or enzymatic depolymerization. Coupling aromatic metabolism to fatty acid biosynthesis makes possible the production of biofuels, oleochemicals, and other fine/bulk chemicals derived from lignin. Our previous work identified Cutaneotrichosporon oleaginosus as a yeast that could accumulate nearly 70% of its dry cell weight as lipids using aromatics as a sole carbon source. Expanding on this, other oleaginous yeast species were investigated for the metabolism of lignin-relevant monoaromatics. Thirty-six oleaginous yeast species from the Phaff yeast collection were screened for growth on several aromatic compounds representing S-, G-, and H- type lignin. The analysis reported in this study suggests that aromatic metabolism is largely segregated to the Cutaenotrichosporon, Trichosporon, and Rhodotorula clades. Each species tested within each clade has different properties with respect to the aromatics metabolized and the concentrations of aromatics tolerated. The combined analysis suggests that Cutaneotrichosporon yeast are the best suited to broad spectrum aromatic metabolism and support its development as a model system for aromatic metabolism in yeast.

Characterization of recombinant laccase from Trametes versicolor synthesized by Arxula adeninivorans and its application in the degradation of pharmaceuticals

Recent years have seen an increasing interest in laccase enzymes. Due to their ability of oxidizing various substrates, they are nowadays applied in multiple industrial fields including pulp delignification, textile dye bleaching, and bioremediation. In contrast to laccase production from native sources, with its generally low yield and high cost, heterologous laccase expression is far better suited to meet the growing industrial demands. TVLCC5 gene encoding Trametes versicolor laccase 5 was overexpressed in Arxula adeninivorans using the strong constitutive TEF1 promoter. Recombinant Tvlcc5 protein was purified by immobilized-metal ion affinity chromatography and biochemically characterized using 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) as substrate for standard activity assays. The enzyme showed the highest activity at 50 °C between pH 4.5–5.5. The half-life of Tvlcc5 at 60 °C was around 20 min. The negative effect of chloride anions on enzyme activity was demonstrated. A fed-batch cultivation of Tvlcc5 producing strain A. adeninivorans G1212/YRC102-TEF1-TVLCC5-6H was performed and resulted in a laccase activity of 4986.3 U L⁻¹. To improve the expression level of recombinant laccase in A. adeninivorans, cultivation conditions were optimized by single factor experiments. Recombinant Tvlcc5 proved to be a promising agent for degradation of pharmaceuticals that are an important source of environmental pollution. Concentration of diclofenac and sulfamethoxazole decreased to 46.8% and 51.1% respectively after 24 h incubation with Tvlcc5. When 1 mM redox mediator ABTS was added complete degradation was obtained within 1 h.

Signal peptide replacement resulted in recombinant homologous expression of laccase Lcc8 in Coprinopsis cinerea

Although the model agaricomycete Coprinopsis cinerea possess 17 different laccase genes, up to now only four C. cinerea laccases have been purified and characterized to some degree. By exchanging the nucleotide sequence of the deduced signal peptide of Lcc8 it was possible to homologously express lcc8 in C. cinerea under control of the Agaricus bisporus gdpII promoter and the C. cinerea lcc1 terminator. The purified Lcc8 showed two bands in the SDS-PAGE with a molecular weight of 64 kDa and 77 kDa, respectively. The IEF determined pI values of 3.3 and 3.4 for both bands. The optimal pH for oxidation of the substrates ABTS, 2,6-dimethoxyphenol, guaiacol and syringaldazine was pH 4.0, pH 5.0, pH 4.5 and pH 5.0, respectively. Best pH for enzyme storage was pH 8.0. The optimal temperature for oxidation of ABTS was 63 °C, while Lcc8 showed activity of at least 50% over 300 min at 50 °C. The comparable high stability of Lcc8 at alkaline pH and higher temperatures can be of interest for biotechnical applications.

Decolorization and detoxification of textile wastewaters by recombinant Myceliophthora thermophila and Trametes trogii laccases

Laccases are multi-copper oxidoreductases with broad biotechnological applications. Here, we report detailed biochemical characterization of purified recombinant laccases originating from Myceliophthora thermophila (MtL) and Trametes trogii (TtL). We identified optimal conditions for decolorization of commercial dyes and textile wastewater samples. We also tested the toxicity of decolorized wastewater samples using human peripheral blood mononuclear cells. MtL and TtL were expressed in Saccharomyces cerevisiae, and secreted enzymes were purified by consecutive hydrophobic and gel chromatography. The molecular masses of TtL (~ 65 kDa) and MtL (> 100 kDa) suggested glycosylation of the recombinant enzymes. Deglycosylation of MtL and TtL led to 25% and 10% decreases in activity, respectively. In a thermal stability assay, TtL retained 61% and MtL 86% of the initial activity at 40 °C. While TtL retained roughly 50% activity at 60 °C, MtL lost stability at temperatures higher than 40 °C. MtL and TtL preferred syringaldazine as a substrate, and the catalytic efficiencies for ABTS oxidation were 7.5 times lower than for syringaldazine oxidation. In the presence of the mediator HBT, purified TtL almost completely decolorized dyes within 30 min and substantially decolorized wastewater samples from a textile factory (up to 74%) within 20 h. However, products of TtL-catalyzed decolorization were more toxic than MtL-decolorized products, which were almost completely detoxified.

Evolution of the feruloyl esterase MtFae1a from Myceliophthora thermophila towards improved catalysts for antioxidants synthesis

The chemical syntheses currently employed for industrial purposes, including in the manufacture of cosmetics, present limitations such as unwanted side reactions and the need for harsh chemical reaction conditions. In order to overcome these drawbacks, novel enzymes are developed to catalyze the targeted bioconversions. In the present study, a methodology for the construction and the automated screening of evolved variants library of a Type B feruloyl esterase from Myceliophthora thermophila (MtFae1a) was developed and applied to generation of 30,000 mutants and their screening for selecting the variants with higher activity than the wild-type enzyme. The library was generated by error-prone PCR of mtfae1a cDNA and expressed in Saccharomyces cerevisiae. Screening for extracellular enzymatic activity towards 4-nitrocatechol-1-yl ferulate, a new substrate developed ad hoc for high-throughput assays of feruloyl esterases, led to the selection of 30 improved enzyme variants. The best four variants and the wild-type MtFae1a were investigated in docking experiments with hydroxycinnamic acid esters using a model of 3D structure of MtFae1a. These variants were also used as biocatalysts in transesterification reactions leading to different target products in detergentless microemulsions and showed enhanced synthetic activities, although the screening strategy had been based on improved hydrolytic activity.

A step forward in laccase exploitation: Recombinant production and evaluation of techno-economic feasibility of the process

Protein heterologous production offers viable opportunities to tailor laccase properties to specific industrial needs. The high redox potential laccase POXA1b from Pleurotus ostreatus was chosen as case study of marketable enzyme, due to its desirable properties in terms of activity/stability profile, and already assessed applicability. POXA1b was heterologously produced in Pichia pastoris by investigating the effect of inducible and constitutive expression systems on both the yield and the cost of its production. System performances were first assessed in shaken-flasks and then scaled-up in bioreactor. The production level obtained in the inducible system is 42U/mL, while the activity value achieved with the constitutive one is 60U/mL, the highest obtained in constitutive systems so far. The economic feasibility of recombinant laccase production was simulated, describing the case of an Italian small-medium enterprise. Two scenarios were evaluated: Scenario (I) production based on methanol inducible system; Scenario (II) production based on the constitutive system, fed with glycerol. At all the scales the glycerol-based fermentation is more economic than the methanol-based one. The price forecast for rPOXA1b production is 0.34€kU^-1 for glycerol-based process, and is very competitive with the current price of commercial laccase.

Upgrading Laccase Production and Biochemical Properties: Strategies and Challenges

Improving laccases continues to be crucial in novel biotechnological developments and industrial applications, where they are concerned. This review breaks down and explores the potential of the strategies (conventional and modern) that can be used for laccase enhancement (increased production and upgraded biochemical properties such as stability and catalytic efficiency). The challenges faced with these approaches are briefly discussed. We also shed light on how these strategies merge and give rise to new options and advances in this field of work. Additionally, this article seeks to serve as a guide for students and academic researchers interested in laccases. This document not only gives basic information on laccases, but also provides updated information on the state of the art of various technologies that are used in this line of investigation. It also gives the readers an idea of the areas extensively studied and the areas where there is still much left to be done. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 33:1015-1034, 2017.

Yeast Hosts for the Production of Recombinant Laccases: A Review

Laccases are multi-copper oxidoreductases which catalyze the oxidation of a wide range of substrates during the simultaneous reduction of oxygen to water. These enzymes, originally found in fungi, plants, and other natural sources, have many industrial and biotechnological applications. They are used in the food, textile, pulp, and paper industries, as well as for bioremediation purposes. Although natural hosts can provide relatively high levels of active laccases after production optimization, heterologous expression can bring, moreover, engineered enzymes with desired properties, such as different substrate specificity or improved stability. Hence, diverse hosts suitable for laccase production are reviewed here, while the greatest emphasis is placed on yeasts which are commonly used for industrial production of various proteins. Different approaches to optimize the laccase expression and activity are also discussed in detail here.

Biodegradation of phenolic compounds by Basidiomycota and its phenol oxidases: A review

The phylum Basidiomycota include organisms with enormous bioremediation potential. A variety of processes were proposed at the lab scale for using these fungi and their phenol oxidases in the degradation of phenolics. Here we present a survey of this topic using literature published mostly over the last 10 years. First, the sources of the enzymes are summarized. The laccase and tyrosinase were mainly from Trametes versicolor and Agaricus bisporus, respectively. Recently, however, new promising wild-type producers of the enzymes have emerged and a number of recombinant strains were also constructed, based mainly on yeasts or Aspergillus strains as hosts. The next part of the study summarizes the enzyme and whole-cell applications for the degradation of phenols, polyphenols, cresols, alkylphenols, naphthols, bisphenols and halogenated (bis)phenols in model mixtures or real wastewaters from the food, paper and coal industries, or municipal and hospital sewage. The enzymes were applied as free (crude or purified) enzymes or as enzymes immobilized in various supports or CLEAs, and optionally recycled or used in continuous mode. Alternatively, growing cultures or harvested mycelia were used instead. The products, which were characterized as quinones and their polymers in some cases, could be eliminated by filtration, flocculation or adsorption onto chitosan. The purity of a treated wastewater was monitored using a sensitive aquatic organism. It is concluded that low-cost sources of these enzymes should be searched for and the benefits of enzymatic, biological and physico-chemical methods could be combined to make the processes fit for industrial use.

Computational analysis and low-scale constitutive expression of laccases synthetic genes GlLCC1 from Ganoderma lucidum and POXA 1B from Pleurotus ostreatus in Pichia pastoris

Lacasses are multicopper oxidases that can catalyze aromatic and non-aromatic compounds concomitantly with reduction of molecular oxygen to water. Fungal laccases have generated a growing interest due to their biotechnological potential applications, such as lignocellulosic material delignification, biopulping and biobleaching, wastewater treatment, and transformation of toxic organic pollutants. In this work we selected fungal genes encoding for laccase enzymes GlLCC1 in Ganoderma lucidum and POXA 1B in Pleurotus ostreatus. These genes were optimized for codon use, GC content, and regions generating secondary structures. Laccase proposed computational models, and their interaction with ABTS [2, 2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid)] substrate was evaluated by molecular docking. Synthetic genes were cloned under the control of Pichia pastoris glyceraldehyde-3-phosphate dehydrogenase (GAP) constitutive promoter. P. pastoris X-33 was transformed with pGAPZαA-LaccGluc-Stop and pGAPZαA-LaccPost-Stop constructs. Optimization reduced GC content by 47 and 49% for LaccGluc-Stop and LaccPost-Stop genes, respectively. A codon adaptation index of 0.84 was obtained for both genes. 3D structure analysis using SuperPose revealed LaccGluc-Stop is similar to the laccase crystallographic structure 1GYC of Trametes versicolor. Interaction analysis of the 3D models validated through ABTS, demonstrated higher substrate affinity for LaccPost-Stop, in agreement with our experimental results with enzymatic activities of 451.08 ± 6.46 UL^-1 compared to activities of 0.13 ± 0.028 UL^-1 for LaccGluc-Stop. This study demonstrated that G. lucidum GlLCC1 and P. ostreatus POXA 1B gene optimization resulted in constitutive gene expression under GAP promoter and α-factor leader in P. pastoris. These are important findings in light of recombinant enzyme expression system utility for environmentally friendly designed expression systems, because of the wide range of substrates that laccases can transform. This contributes to a great gamut of products in diverse settings: industry, clinical and chemical use, and environmental applications.

Development of an improved variant of GH51 α-l-arabinofuranosidase from Pleurotus ostreatus by directed evolution

In this study, the α-l-arabinofuranosidase from Pleurotus ostreatus was subjected to directed evolution by expressing a library of around 7000 randomly mutated variants by error prone Polymerase Chain Reaction. High-throughput screening of the library for the most active variants was performed by assaying activity towards p-nitrophenyl α-l-arabinofuranoside, and a variant with higher activity than the wild type was selected, purified and characterised. It exhibited a kcat of 7.3 ×1 0¹ ± 0.3 min⁻¹, around 3-fold higher than that of the wild type (2.2 × 10³ ± 0.2 min⁻¹), and a KM (0.54 ± 0.0 6mM) 30% lower than that of the wild type (0.70 ± 0.05 mM) towards this substrate. The mutant also showed improved catalytic properties towards pNP-β-d-glucopyranoside (kcat of 50.85 ± 0.21 min⁻¹ versus 11.0 ± 0.6 min⁻¹) and it was shown able to hydrolyse larch arabinogalactan which is not recognised by the wild type. The mutant was also more active than the wild type towards arabinoxylan and was able to hydrolyse arabinan, which was not transformed by the wild type. The ability of rPoAbf F435Y/Y446F to hydrolyse these insoluble substrates expands its potential for application also to hemicelluloses, which in some types of pretreatment are recovered in solid fractions.

Effective mutations in a high redox potential laccase from Pleurotus ostreatus

Since the first report on a laccase, there has been a notable development in the interest towards this class of enzymes, highlighted from the number of scientific papers and patents about them. At the same time, interest in exploiting laccases-mainly high redox potential-for various functions has been growing exponentially over the last 10 years. Despite decades of work, the molecular determinants of the redox potential are far to be fully understood. For this reason, interest in tuning laccase redox potential to provide more efficient catalysts has been growing since the last years. The work herein described takes advantage of the filamentous fungus Aspergillus niger as host for the heterologous production of the high redox potential laccase POXA1b from Pleurotus ostreatus and of one of its in vitro selected variants (1H6C). The system herein developed allowed to obtain a production level of 35,000 U/L (583.3 μkat/L) for POXA1b and 60,000 U/L (1,000 μkat/L) for 1H6C, corresponding to 13 and 20 mg/L for POXA1b and 1H6C, respectively. The characterised proteins exhibit very similar characteristics, with some exceptions regarding catalytic behaviour, stability and spectro-electrochemical properties. Remarkably, the 1H6C variant shows a higher redox potential with respect to POXA1b. Furthermore, the spectro-electrochemical results obtained for 1H6C make it tempting to claim that we spectro-electrochemically determined the redox potential of the 1H6C T2 site, which has not been studied in any detail by spectro-electrochemistry yet.

Molecular adaptation mechanisms employed by ethanologenic bacteria in response to lignocellulose-derived inhibitory compounds

Current international interest in finding alternative sources of energy to the diminishing supplies of fossil fuels has encouraged research efforts in improving biofuel production technologies. In countries which lack sufficient food, the use of sustainable lignocellulosic feedstocks, for the production of bioethanol, is an attractive option. In the pre-treatment of lignocellulosic feedstocks for ethanol production, various chemicals and/or enzymatic processes are employed. These methods generally result in a range of fermentable sugars, which are subjected to microbial fermentation and distillation to produce bioethanol. However, these methods also produce compounds that are inhibitory to the microbial fermentation process. These compounds include products of sugar dehydration and lignin depolymerisation, such as organic acids, derivatised furaldehydes and phenolic acids. These compounds are known to have a severe negative impact on the ethanologenic microorganisms involved in the fermentation process by compromising the integrity of their cell membranes, inhibiting essential enzymes and negatively interact with their DNA/RNA. It is therefore important to understand the molecular mechanisms of these inhibitions, and the mechanisms by which these microorganisms show increased adaptation to such inhibitors. Presented here is a concise overview of the molecular adaptation mechanisms of ethanologenic bacteria in response to lignocellulose-derived inhibitory compounds. These include general stress response and tolerance mechanisms, which are typically those that maintain intracellular pH homeostasis and cell membrane integrity, activation/regulation of global stress responses and inhibitor substrate-specific degradation pathways. We anticipate that understanding these adaptation responses will be essential in the design of 'intelligent' metabolic engineering strategies for the generation of hyper-tolerant fermentation bacteria strains.

Transgenic tobacco plants expressing a fungal laccase are able to reduce phenol content from olive mill wastewaters

A biotechnological approach was applied to reduce phenol content in olive mill wastewaters by transgenic tobacco plants. The cDNA laccase of poxC gene from Pleurotus ostreatus, carrying its own signal peptide for extracellular secretion, was transferred into the Nicotiana tabacum genome. Transgenic tobacco plants were obtained and the recombinant enzyme was secreted into the rhizosphere by the plant root apparatus, confirming the ability of the plant machinery to recognize the fungal POXC peptide signal leader appropriately as secretory tag. Total laccase activity assayed by ABTS in transgenic lines increased sharply compared to control plants. Moreover, plants cultivated in a hydroponic solution with the addition of olive mill wastewaters were able to reduce the total phenol content up to 70%.

Transcriptional and enzymatic profiling of Pleurotus ostreatus laccase genes in submerged and solid-state fermentation cultures

The genome of the white rot basidiomycete Pleurotus ostreatus includes 12 phenol oxidase (laccase) genes. In this study, we examined their expression profiles in different fungal strains under different culture conditions (submerged and solid cultures) and in the presence of a wheat straw extract, which was used as an inducer of the laccase gene family. We used a reverse transcription-quantitative PCR (RT-qPCR)-based approach and focused on determining the reaction parameters (in particular, the reference gene set for the normalization and reaction efficiency determinations) used to achieve an accurate estimation of the relative gene expression values. The results suggested that (i) laccase gene transcription is upregulated in the induced submerged fermentation (iSmF) cultures but downregulated in the solid fermentation (SSF) cultures, (ii) the Lacc2 and Lacc10 genes are the main sources of laccase activity in the iSmF cultures upon induction with water-soluble wheat straw extracts, and (iii) an additional, as-yet-uncharacterized activity (Unk1) is specifically induced in SSF cultures that complements the activity of Lacc2 and Lacc10. Moreover, both the enzymatic laccase activities and the Lacc gene family transcription profiles greatly differ between closely related strains. These differences can be targeted for biotechnological breeding programs for enzyme production in submerged fermentation reactors.

Engineered tobacco and microalgae secreting the fungal laccase POXA1b reduce phenol content in olive oil mill wastewater

Olive oil mill wastewaters (OMWs) are characterised by low pH and a high content of mono- and polyaromatic compounds that exert microbial and phytotoxic activity. The laccase cDNA of the poxA1b gene from Pleurotus ostreatus, carrying a signal peptide sequence for enzyme secretion and driven by the CaMV 35S promoter, was cloned into a plant expression vector. Nuclear genetic transformation was carried out by co-cultivation of Agrobacterium tumefaciens with tobacco cv Samsun NN leaves and cells of five different microalgae accessions belonging to the genera Chlamydomonas, Chlorella and Ankistrodesmus. Transgenic plants and microalgae were able to express and secrete the recombinant laccase in the root exudates and the culture medium, respectively. In comparison to untransformed controls, the ability to reduce phenol content in OMW solution was enhanced up to 2.8-fold in transgenic tobacco lines and by up to about 40% in two microalgae accessions. The present work provides new evidence for metabolic improvement of green organisms through the transgenic approach to remediation.

A chloride tolerant laccase from the plant pathogen ascomycete Botrytis aclada expressed at high levels in Pichia pastoris

Fungal laccases from basidiomycetous fungi are thoroughly investigated in respect of catalytic mechanism and industrial applications, but the number of reported and well characterized ascomycetous laccases is much smaller although they exhibit interesting catalytic properties. We report on a highly chloride tolerant laccase produced by the plant pathogen ascomycete Botrytis aclada, which was recombinantly expressed in Pichia pastoris with an extremely high yield and purified to homogeneity. In a fed-batch fermentation, 495 mg L(-1) of laccase was measured in the medium, which is the highest concentration obtained for a laccase by a yeast expression system. The recombinant B. aclada laccase has a typical molecular mass of 61,565 Da for the amino acid chain. The pI is approximately 2.4, a very low value for a laccase. Glycosyl residues attached to the recombinant protein make up for approximately 27% of the total protein mass. B. aclada laccase exhibits very low K(M) values and high substrate turnover numbers for phenolic and non-phenolic substrates at acidic and near neutral pH. The enzyme's stability increases in the presence of chloride ions and, even more important, its substrate turnover is only weakly inhibited by chloride ions (I(50)=1.4M), which is in sharp contrast to most other described laccases. This high chloride tolerance is mandatory for some applications such as implantable biofuel cells and laccase catalyzed reactions, which suffer from the presence of chloride ions. The high expression yield permits fast and easy production for further basic and applied research.

A family GH51 α-L-arabinofuranosidase from Pleurotus ostreatus: identification, recombinant expression and characterization

An α-L-arabinofuranosidase produced by Pleurotus ostreatus (PoAbf) during solid state fermentation on tomato pomace was identified and the corresponding gene and cDNA were cloned and sequenced. Molecular analysis showed that the poabf gene carries 26 exons interrupted by 25 introns and has an open reading frame encoding a protein of 646 amino acid residues, including a signal peptide of 20 amino acid residues. The amino acid sequence similar to the other α-L-arabinofuranosidases indicated that the enzyme encoded by poabf can be classified as a family 51 glycoside hydrolase. Heterologous recombinant expression of PoAbf was carried out in the yeasts Pichia pastoris and Kluyveromyces lactis achieving the highest production level of the secreted enzyme (180 mg L(-1)) in the former host. rPoAbf produced in P. pastoris was purified and characterized. It is a glycosylated monomer with a molecular weight of 81,500 Da in denaturing conditions. Mass spectral analyses led to the localization of a single O-glycosylation site at the level of Ser160. The enzyme is highly specific for α-L-arabinofuranosyl linkages and when assayed with p-nitrophenyl α-L-arabinofuranoside it follows Michaelis-Menten kinetics with a K (M) of 0.64 mM and a k (cat) of 3,010 min(-1). The optimum pH is 5 and the optimal temperature 40°C. It is worth noting that the enzyme shows a very high stability in a broad range of pH. The more durable activity showed by rPoAbf in comparison to the other α-L-arabinofuranosidases enhances its potential for biotechnological applications and increases interest in elucidating the molecular bases of its peculiar properties.

Engineering laccases: in search for novel catalysts

Laccases (p-diphenol oxidase, EC 1.10.3.2) are blue multicopper oxidases that catalyze the reduction of dioxygen to water, with a concomitant oxidation of small organic substrates. Since the description at the end of the nineteenth century of a factor catalyzing the rapid hardening of the latex of the Japanese lacquer trees (Rhus sp.) exposed to air laccases from different origins (plants, fungi bacteria) have been continuously discovered and extensively studied. Nowadays, molecular evolution and other powerful protein modification techniques offer possibilities to develop tailored laccases for a wide array of applications including drug synthesis, biosensors or biofuel cells. Here, we give an overview on strategies and results of our laboratory in the design of new biocatalysts based on laccases.

Heterologous laccase production and its role in industrial applications

Laccases are blue multicopper oxidases, catalyzing the oxidation of an array of aromatic substrates concomitantly with the reduction of molecular oxygen to water. These enzymes are implicated in a variety of biological activities. Most of the laccases studied thus far are of fungal origin. The large range of substrates oxidized by laccases has raised interest in using them within different industrial fields, such as pulp delignification, textile dye bleaching, and bioremediation. Laccases secreted from native sources are usually not suitable for large-scale purposes, mainly due to low production yields and high cost of preparation/purification procedures. Heterologous expression may provide higher enzyme yields and may permit to produce laccases with desired properties (such as different substrate specificities, or improved stabilities) for industrial applications. This review surveys researches on heterologous laccase expression focusing on the pivotal role played by recombinant systems towards the development of robust tools for greening modern industry.

Multiple multi-copper oxidase gene families in basidiomycetes - what for?

Genome analyses revealed in various basidiomycetes the existence of multiple genes for blue multi-copper oxidases (MCOs). Whole genomes are now available from saprotrophs, white rot and brown rot species, plant and animal pathogens and ectomycorrhizal species. Total numbers (from 1 to 17) and types of mco genes differ between analyzed species with no easy to recognize connection of gene distribution to fungal life styles. Types of mco genes might be present in one and absent in another fungus. Distinct types of genes have been multiplied at speciation in different organisms. Phylogenetic analysis defined different subfamilies of laccases sensu stricto (specific to Agaricomycetes), classical Fe2+-oxidizing Fet3-like ferroxidases, potential ferroxidases/laccases exhibiting either one or both of these enzymatic functions, enzymes clustering with pigment MCOs and putative ascorbate oxidases. Biochemically best described are laccases sensu stricto due to their proposed roles in degradation of wood, straw and plant litter and due to the large interest in these enzymes in biotechnology. However, biological functions of laccases and other MCOs are generally little addressed. Functions in substrate degradation, symbiontic and pathogenic intercations, development, pigmentation and copper homeostasis have been put forward. Evidences for biological functions are in most instances rather circumstantial by correlations of expression. Multiple factors impede research on biological functions such as difficulties of defining suitable biological systems for molecular research, the broad and overlapping substrate spectrum multi-copper oxidases usually possess, the low existent knowledge on their natural substrates, difficulties imposed by low expression or expression of multiple enzymes, and difficulties in expressing enzymes heterologously.

A semi-rational approach to engineering laccase enzymes

In order to develop improved laccase-based bio-catalysts, semi-rational mutagenesis of the laccase POXA1b from Pleurotus ostreatus was performed through a combination of directed evolution with elements of rational enzyme modification. The R4 laccase was prepared by joining mutations of previously selected POXA1b random variants. An enhancement of stability features was thus obtained, making the novel enzyme R4 more appropriate as scaffold for directed evolution. A library of 1000 randomly mutated variants of R4 was prepared and screened for the ability of oxidising 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS). One of the variants selected (V148L) for improved activity was also proved to show higher stability than R4 at pH 5, and to retain its high stability at pH 7 and 10. In comparison with the POXA1b wild-type laccase, the semi-rational approach allowed us to develop a more efficient bio-catalyst, rising specific activity on ABTS up to around 5-fold. The new variant was also proved to be both more versatile and more durable than the wild-type enzyme, exhibiting higher activity in wide temperature and pH ranges and higher stability at acidic (t (1/2) at pH 5 = 35 days), neutral (t (1/2) at pH 7 = 38 days) and alkaline (t (1/2) at pH 10 = 62 days) pH values.

Laccases: a never-ending story

Laccases (benzenediol:oxygen oxidoreductases, EC 1.10.3.2) are blue multicopper oxidases that catalyze the oxidation of an array of aromatic substrates concomitantly with the reduction of molecular oxygen to water. In fungi, laccases carry out a variety of physiological roles during their life cycle. These enzymes are being increasingly evaluated for a variety of biotechnological applications due to their broad substrate range. In this review, the most recent studies on laccase structural features and catalytic mechanisms along with analyses of their expression are reported and examined with the aim of contributing to the discussion on their structure-function relationships. Attention has also been paid to the properties of enzymes endowed with unique characteristics and to fungal laccase multigene families and their organization.