Use of Feruloyl Esterase as Laccase-Mediator System in Paper Bleaching

Recovery of green phenolic compounds from lignin-based source: Role of ferulic acid esterase towards waste valorization and bioeconomic perspectives

The production of chemicals/products so far relies on fossil-based resources with the creation of several environmental problems at the global level. In this situation, a sustainable and circular economy model is necessitated to mitigate global environmental issues. Production of biowaste from various processing industries also creates environmental issues which would be valorized for the production of industrially important reactive and bioactive compounds. Lignin acts as a vital part in biowaste composition which can be converted into a wide range of phenolic compounds. The phenolic compounds have attracted much attention, owing to their influence on diverse not only organoleptic parameters, such as taste or color, but also active agents for active packaging systems. Crop residues of varied groups, which are an affluent source of lignocellulosic biomass could serve as a renewable resource for the biosynthesis of ferulic acid (FA). FA is obtained by the FA esterase enzyme action, and it can be further converted into various tail end phenolic flavor green compounds like vanillin, vanillic acid and hydroxycinnamic acid. Lignin being renewable in nature, processing and management of biowastes towards sustainability is the need as far as the global industrial point is concerned. This review explores all the approaches for conversion of lignin into value-added phenolic compounds that could be included to packaging applications. These valorized products can exhibit the antioxidant, antimicrobial, cardioprotective, anti-inflammatory and anticancer properties, and due to these features can emerge to incorporate them into production of functional foods and be utilization of them at active food packaging application. These approaches would be an important step for utilization of the recovered bioactive compounds at the nutraceutical and food industrial sectors.

Multiple strategies to improve extracellular secretion and activity of feruloyl esterase

Feruloyl esterase has a wide range of applications, but there are still problems with low enzyme yield and activity, and complex purification steps. Our previous research found Lactobacillus amylovorus feruloyl esterase could be secreted extracellular in Escherichia coli. In this study, multiple strategies were implemented to maximize the extracellular production of feruloyl esterase with improved activity in E. coli. Firstly, codon-optimized feruloyl esterase was obtained based on the preference of E. coli, resulting in 41.97 % increase in extracellular secretion. Furthermore, by cascading T7 promoters, replacing the 5' UTR, randomly mutating the N-terminal sequence, and co-expressing secretory cofactors, the extracellular secretion was increased by 36.46 %, 31.25 %, 20.66 % and 25.75 %, respectively. Moreover, the feruloyl esterase were mutated to improve the substrate affinity and activity. The catalytic efficiency of Fae-Q134T and Fae-Q198A increased by 4.62-fold and 5.42-fold. Combining above strategies, extracellular feruloyl esterase activity was increased from 2013.70 U/L to 10,349.04 U/L. These results indicated that the activity and yield of feruloyl esterase secreted by E. coli were significantly increased, which laid a foundation for its industrial application.

Systematic bioprospection for cellulolytic actinomycetes in the Chihuahuan Desert: isolation and enzymatic profiling

The quest for microbial cellulases has intensified as a response to global challenges in biofuel production. The efficient deconstruction of lignocellulosic biomass holds promise for generating valuable products in various industries such as food, textile, and detergents. This article presents a systematic bioprospection aimed at isolating actinomycetes with exceptional cellulose deconstruction capabilities. Our methodology explored the biodiverse oligotrophic region of Cuatro Cienegas, Coahuila, within the Chihuahuan Desert. Among the evaluated actinomycetes collection, 78% exhibited cellulolytic activity. Through a meticulous screening process based on enzymatic index evaluation, we identified a highly cellulolytic Streptomyces strain for further investigation. Submerged fermentation of this strain revealed an endoglucanase enzymatic activity of 149 U/mg. Genomic analysis of strain Streptomyces sp. STCH565-A revealed unique configurations of carbohydrate-active enzyme (CAZyme) genes, underscoring its potential for lignocellulosic bioconversion applications. These findings not only highlight the significance of the Chihuahuan Desert as a rich source of cellulolytic microorganisms but also offer insights into the systematic exploration and selection of high-performing cellulolytic microorganisms for application in diverse environmental contexts. In conclusion, our bioprospecting study lays a foundation for harnessing the cellulolytic potential of actinomycetes from the Chihuahuan Desert, with implications for advancing cellulose deconstruction processes in various industries. The findings can serve as a blueprint for future bioprospecting efforts in different regions, facilitating the targeted discovery of microorganisms with exceptional cellulosic deconstruction capabilities.

Isolation of functional ligninolytic Bacillus aryabhattai from paper mill sludge and its lignin degradation potential

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Isolation of a functional lignin-degrading Bacillus aryabhattai.

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Production of growth-associated LiP and MnP enzymes.

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Almost 84% KL degradation at 500 mg L⁻¹ KL concentration.

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KL biodegradation process was revealed by chemical analysis.

Kraft lignin (KL), is the major pollutant in pulp and paper effluent and due to its heterogeneous structure, it is resistant to the depolymerization process. It has drawn much attention from the researcher due to its challenging degradation process. In this study, a KL-degrading bacterium was isolated and screened from paper mill sludge. This bacterium was identified as ligninolytic Bacillus aryabhattai using biochemical and 16SrRNA gene analysis. B. aryabhattai showed maximum activities of lignin peroxidase-LiP (0.74 IU mL⁻¹) and manganese peroxidase-MnP (9.2 IU mL⁻¹) on the 4th day, and 5th day, respectively. A total 84% of KL (500 mg L⁻¹) reduction was observed after 14 days. The KL bio-degradation was confirmed based on changes in chemical stracture of KL and new metabolites identification using FTIR and GC–MS, respectively. The study concluded that B. aryabhattai maybe becomes a potential biological agent in KL biodegradation and treatment of other lignin-containing industrial effluents.

Catalytic roles, immobilization and management of recalcitrant environmental pollutants by laccases: Significance in sustainable green chemistry

We are facing a high risk of exposure to emerging contaminants and increasing environmental pollution with the concomitant growth of industries. Persistence of these pollutants is a major concern to the ecosystem. Laccases, also known as "green catalysts" are multi-copper oxidases which offers an eco-friendly solution for the degradation of these hazardous pollutants to less or non-toxic compounds. Although various other biological methods exist for the treatment of pollutants, the fact that laccases catalyze the oxidation of broad range of substrates in the presence of molecular oxygen without any additional cofactor and releases water as the by-product makes them exceptional. They have a good possibility of utilization in various industries, especially for the purpose of bioremediation. Besides this, they have also been used in medical/health care, food industry, bio-bleaching, wine stabilization, organic synthesis and biosensors. This review covers the catalytic behaviour of laccases, their immobilization strategies, potential applications in bioremediation of recalcitrant environmental pollutants and their engineering. It provides a comprehensive summary of most factors to consider while working with laccases in an industrial setting. It compares the benefits and drawbacks of the current techniques. Immobilization and mediators, two of the most significant aspects in working with laccases, have been meticulously discussed.

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.

Nanomaterial conjugated lignocellulosic waste: cost-effective production of sustainable bioenergy using enzymes

The demand for novel and renewable sources of energy has increased as a result of rapid population growth, limited sources of bioenergy, and environmental pollution, caused by excessive use of fossil fuels. The need to meet future energy demands have motivated researchers to search for alternative and sustainable sources of energy. The bioconversion of lignocellulosic waste (agricultural and food waste) into biofuels shows competitive promises. Lignocellulosic waste is easily accessible and has a large enzyme system that can be immobilised onto nano-matrices. Consequently, resulting in higher biofuel production and process efficiency. However, the excessive production cost of the current procedures, which involve physical, chemical, and enzymatic reactions, is limited. The use of nanomaterials has recently been shown to concentrate lignocellulosic waste, therefore, reviewing the quest for efficient production of sustainable and cost-effective development of bioenergy from lignocellulosic wastes. This review paper explores the advanced strategies of using nanobiotechnology to combine enzyme-conjugated nanosystems for the cost-effective production of sustainable bioenergy solutions. This research will help to develop an inexpensive, eco-friendly technology for biofuels production and also help overcome the environmental burden of lignocellulosic waste worldwide.

Cloning, expression and biochemical characterization of lignin-degrading DyP-type peroxidase from Bacillus sp. Strain BL5

Lignin is a major byproduct of pulp and paper industries, which is resistant to depolymerization due to its heterogeneous structure. The enzymes peroxidases can be utilized as potent bio-catalysts to degrade lignin. In the current study, an Efeb gene of 1251bp encoding DyP-type peroxidase from Bacillus sp. strain BL5 (DyPBL5) was amplified, cloned into a pET-28a (+) vector and expressed in Escherichia coli BL21 (DE3) cells. A 46 kDa protein of DyPBL5 was purified through ion-exchange chromatography. Purified DyPBL5 was active at wide temperature (25-50 °C) and pH (3.0-8.0) range with optimum activity at 35 °C and pH 5.0. Effects of different chemicals on DyPBL5 were determined. The enzyme activity was strongly inhibited by SDS, DDT and β-mercaptoethanol, whereas stimulated in the presence of organic solvents such as methanol and ethanol. The kinetic parameters were determined and K_m, V_max and K_cat values were 1.06 mM, 519.75 μmol/min/mg and 395 S̶ ¹, respectively. Docking of DyPBL5 with ABTS revealed that, Asn 244, Arg 339, Asp 383 and Thr 389 are putative amino acids, taking part in the oxidation of ABTS. The recombinant DyPBL5 resulted in the reduction of lignin contents up to 26.04 %. The SEM and FT-IR analysis of test samples gave some indications about degradation of lignin by DyPBL5. Various low molecular weight lignin degradation products were detected by analyzing the samples through gas chromatography mass spectrometry. High catalytic efficiency and lignin degradation rate make DyPBL5 an ideal bio-catalyst for remediation of lignin-contaminated sites.

Expression of an alkaline feruloyl esterases from thermophilic Chaetomium thermophilum and its boosting effect on delignification of pulp

Exploration of feruloyl esterase (FAE) with the resistance to heat and alkali conditions in biobleaching process to improve the separation efficiency of lignocellulose is the key to achieving green papermaking. Herein, we expressed FAEB of C. thermophilum and obtained a thermostable alkaline FAE that can effectively promote the removal of lignin from pulp. The faeB gene was successfully obtained through genomic Blast strategy and high-efficiency expressed under the control of strong alcohol oxidase promoter in Pichia pastoris. The recombinant CtFAEB has an optimal temperature of 65 °C and pH of 7.0. After treated at 65 °C for 1 h, CtFAEB can still retain 63.21 % of its maximum activity, showing a good thermal stability. In addition, the recombinant CtFAEB has broad pH stability and can retain about 56 % of the maximum activity even at pH 11.0. Compared with the effect of mesophilic FAE, pretreatment with thermostable CtFAEB can promote the delignification by laccase and alkaline hydrogen peroxide from the pulp at 70 °C and pH 9.0. Alignment of the protein sequences of CtFAEB and mesophilic FAE suggested that the percentage of amino acids that easily form alpha helix in CtFAEB increases, which enhances its structural rigidity and thereby improves its thermal stability and alkali tolerance. Our study provides an effective method to obtain thermostable and alkaline FAEs, which will promote its application in biobleaching and other biorefining industries.

Purification and Characterization of a Thermo- and pH-Stable Laccase From the Litter-Decomposing Fungus Gymnopus luxurians and Laccase Mediator Systems for Dye Decolorization

An extracellular laccase (GLL) was purified from fermentation broth of the litter-decomposing fungus Gymnopus luxurians by four chromatography steps, which resulted in a high specific activity of 118.82 U/mg, purification fold of 41.22, and recovery rate of 42.05%. It is a monomeric protein with a molecular weight of 64 kDa and N-terminal amino acid sequence of AIGPV TDLHI, suggesting that GLL is a typical fungal laccase. GLL demonstrated an optimum temperature range of 55°C-65°C and an optimum pH 2.2 toward 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS). It displayed considerably high thermostability and pH stability with about 63% activity retained after 24 h at 50°C, and 86% activity retained after 24 h at pH 2.2, respectively. GLL was significantly enhanced in the presence of K+, Na+, and Mg2+ ions. It demonstrated K m of 539 μM and k cat /K m of 140 mM-1⋅s-1 toward ABTS at pH 2.2 and 37°C. Acetosyringone (AS) and syringaldehyde (SA) were the optimal mediators of GLL (0.4 U/ml) for dye decolorization with decolorization rates of about 60%-90% toward 11 of the 14 synthetic dyes. The optimum reaction conditions were determined to be mediator concentration of 0.1 mM, temperature range of 25°C -60°C, and pH 4.0. The purified laccase was the first laccase isolated from genus Gymnopus with high thermostability, pH stability, and effective decolorization toward dyes, suggesting that it has potentials for textile and environmental applications.

Biobleaching: An eco-friendly approach to reduce chemical consumption and pollutants generation

The pulp and paper industry is known to be a large contributor to environmental pollution due to the huge consumption of chemicals and energy. Several chemicals including H2SO4, Cl2, ClO2, NaOH, and H2O2 are used during the bleaching process. These chemicals react with lignin and carbohydrates to generate a substantial amount of pollutants in bleach effluents. Environmental pressure has compelled the pulp and paper industry to reduce pollutant generation from the bleaching section. Enzymes have emerged as simple, economical, and eco-friendly alternatives for bleaching of pulp. The pretreatment of pulp with enzymes is termed as biobleaching or pre-bleaching. Different microbial enzymes such as xylanases, pectinases, laccases, manganese peroxidases (MnP), and lignin peroxidases are used for biobleaching. Xylanases depolymerize the hemicelluloses precipitated on pulp fiber surfaces and improves the efficiency of bleaching chemicals. Xylanase treatment also increases the pulp fibrillation and reduces the beating time of the pulp. Pectinases hydrolyze pectin available in the pulp fibers and improve the papermaking process. Laccase treatment is found more effective along with mediator molecules (as a laccase-mediator system). Biobleaching of pulp results in the superior quality of pulp along with lower consumption of chlorine-based chemicals and lower generation of adsorbable organic halidesadsorbable organic halides (AOX. An enzyme pretreatment reduces the kappa number of pulp and improves ISO brightness significantly. Better physical strength properties and pulp viscosity have also been observed during biobleaching of pulp.

Tree bark scrape fungus: A potential source of laccase for application in bioremediation of non-textile dyes

Although laccase has been recognized as a wonder molecule and green enzyme, the use of low yielding fungal strains, poor production, purification, and low enzyme kinetics have hampered its large-scale application. Thus,this study aims to select high yielding fungal strains and optimize the production, purification, and kinetics of laccase of Aspergillus sp. HB_RZ4. The results obtained indicated that Aspergillus sp. HB_RZ4 produced a significantly large amount of laccase under meso-acidophilic shaking conditions in a medium containing glucose and yeast extract. A 25 μM CuSO4 was observed to enhance the enzyme yield. The enzyme was best purified on a Sephadex G-100 column. The purified enzyme resembled laccase of A. flavus. The kinetics of the purified enzyme revealed high substrate specificity and good velocity of reaction,using ABTS as a substrate. The enzyme was observed to be stable over various pH values and temperatures. The peptide structure of the purified enzyme was found to resemble laccase of A. kawachii IFO 4308. The fungus was observed to decolorize various dyes independent of the requirement of a laccase mediator system.Aspergillus sp. HB_RZ4 was observed to be a potent natural producer of laccase, and it decolorized the dyes even in the absence of a laccase mediator system. Thus, it can be used for bioremediation of effluent that contains non-textile dyes.

Ligninolytic enzymes and its mechanisms for degradation of lignocellulosic waste in environment

Ligninolytic enzymes play a key role in degradation and detoxification of lignocellulosic waste in environment. The major ligninolytic enzymes are laccase, lignin peroxidase, manganese peroxidase, and versatile peroxidase. The activities of these enzymes are enhanced by various mediators as well as some other enzymes (feruloyl esterase, aryl-alcohol oxidase, quinone reductases, lipases, catechol 2, 3-dioxygenase) to facilitate the process for degradation and detoxification of lignocellulosic waste in environment. The structurally laccase is isoenzymes with monomeric or dimeric and glycosylation levels (10–45%). This contains four copper ions of three different types. The enzyme catalyzes the overall reaction: 4 benzenediol + O₂ to 4 benzosemiquinone + 2H₂O. While, lignin peroxidase is a glycoprotein molecular mass of 38–46 kDa containing one mole of iron protoporphyrin IX per one mol of protein, catalyzes the H₂O₂ dependent oxidative depolymerization of lignin. The manganese peroxidase is a glycosylated heme protein with molecular mass of 40–50kDa. It depolymerizes the lignin molecule in the presence of manganese ion. The versatile peroxidase has broad range substrate sharing typical features of the manganese and lignin peroxidase families. Although ligninolytic enzymes have broad range of industrial application specially the degradation and detoxification of lignocellulosic waste discharged from various industrial activities, its large scale application is still limited due to lack of limited production. Further, the extremophilic properties of ligninolytic enzymes indicated their broad prospects in varied environmental conditions. Therefore it needs more extensive research for understanding its structure and mechanisms for broad range commercial applications.