Potential applications of laccase-mediated coupling and grafting reactions: A review

Genome-wide analysis of the common bean (Phaseolus vulgaris) laccase gene family and its functions in response to abiotic stress

BACKGROUND

Laccase (LAC) gene family plays a pivotal role in plant lignin biosynthesis and adaptation to various stresses. Limited research has been conducted on laccase genes in common beans.

RESULTS

29 LAC gene family members were identified within the common bean genome, distributed unevenly in 9 chromosomes. These members were divided into 6 distinct subclades by phylogenetic analysis. Further phylogenetic analyses and synteny analyses indicated that considerable gene duplication and loss presented throughout the evolution of the laccase gene family. Purified selection was shown to be the major evolutionary force through Ka / Ks. Transcriptional changes of PvLAC genes under low temperature and salt stress were observed, emphasizing the regulatory function of these genes in such conditions. Regulation by abscisic acid and gibberellins appears to be the case for PvLAC3, PvLAC4, PvLAC7, PvLAC13, PvLAC14, PvLAC18, PvLAC23, and PvLAC26, as indicated by hormone induction experiments. Additionally, the regulation of PvLAC3, PvLAC4, PvLAC7, and PvLAC14 in response to nicosulfuron and low-temperature stress were identified by virus-induced gene silence, which demonstrated inhibition on growth and development in common beans.

CONCLUSIONS

The research provides valuable genetic resources for improving the resistance of common beans to abiotic stresses and enhance the understanding of the functional roles of the LAC gene family.

Green nanobiocatalysts: enhancing enzyme immobilization for industrial and biomedical applications

Nanobiocatalysts (NBCs), which merge enzymes with nanomaterials, provide a potent method for improving enzyme durability, efficiency, and recyclability. This review highlights the use of eco-friendly synthesis methods to create sustainable nanomaterials for enzyme transport. We investigate different methods of immobilization, such as adsorption, ionic and covalent bonding, entrapment, and cross-linking, examining their pros and cons. The decreased environmental impact of green-synthesized nanomaterials from plants, bacteria, and fungi is emphasized. The review exhibits the various uses of NBCs in food industry, biofuel production, and bioremediation, showing how they can enhance effectiveness and eco-friendliness. Furthermore, we explore the potential impact of NBCs in biomedicine. In general, green nanobiocatalysts are a notable progression in enzyme technology, leading to environmentally-friendly and effective biocatalytic methods that have important impacts on industrial and biomedical fields.

Enzymatic degradability of diclofenac ozonation products: A mechanistic analysis

The treatment of waterborne micropollutants, such as diclofenac, presents a significant challenge to wastewater treatment plants due to their incomplete removal by conventional methods. Ozonation is an effective technique for the degradation of micropollutants. However, incomplete oxidation can lead to the formation of ecotoxic by-products that require a subsequent post-treatment step. In this study, we analyze the susceptibility of micropollutant ozonation products to enzymatic digestion with laccase from Trametes versicolor to evaluate the potential of enzymatic treatment as a post-ozonation step. The omnipresent micropollutant diclofenac is used as an example, and the enzymatic degradation kinetics of all 14 detected ozonation products are analyzed by high-performance liquid chromatography coupled with high-resolution mass spectrometry (HPLC-HRMS) and tandem mass spectrometry (MS2). The analysis shows that most of the ozonation products are responsive to chemo-enzymatic treatment but show considerable variation in enzymatic degradation kinetics and efficiencies. Mechanistic investigation of representative transformation products reveals that the hydroxylated aromatic nature of the ozonation products matches the substrate spectrum, facilitating their rapid recognition as substrates by laccase. However, after initiation by laccase, the subsequent chemical pathway of the enzymatically formed radicals determines the global degradability observed in the enzymatic process. Substrates capable of forming stable molecular oxidation products inhibit complete detoxification by oligomerization. This emphasizes that it is not the enzymatic uptake of the substrates but the channelling of the reaction of the substrate radicals towards the oligomerization of the substrate radicals that is the key step in the further development of an enzymatic treatment step for wastewater applications.

Enzymatic crosslinking of lignin nanoparticles and nanocellulose in cryogels improves adsorption of pharmaceutical pollutants

Pharmaceuticals, designed for treating diseases, ironically endanger humans and aquatic ecosystems as pollutants. Adsorption-based wastewater treatment could address this problem, however, creating efficient adsorbents remains a challenge. Recent efforts have shifted towards sustainable bio-based adsorbents. Here, cryogels from lignin-containing cellulose nanofibrils (LCNF) and lignin nanoparticles (LNPs) were explored as pharmaceuticals adsorbents. An enzyme-based approach using laccase was used for crosslinking instead of fossil-based chemical modification. The impact of laccase treatment on LNPs alone produced surface-crosslinked water-insoluble LNPs with preserved morphology and a hemicellulose-rich, water-soluble LNP fraction. The water-insoluble LNPs displayed a significant increase in adsorption capacity, up to 140 % and 400 % for neutral and cationic drugs, respectively. The crosslinked cryogel prepared by one-pot incubation of LNPs, LCNF and laccase showed significantly higher adsorption capacities for various pharmaceuticals in a multi-component system than pure LCNF or unmodified cryogels. The crosslinking minimized the leaching of LNPs in water, signifying enhanced binding between LNPs and LCNF. In real wastewater, the laccase-modified cryogel displayed 8-44 % removal for cationic pharmaceuticals. Overall, laccase treatment facilitated the production of bio-based adsorbents by improving the deposition of LNPs to LCNF. Finally, this work introduces a sustainable approach for engineering adsorbents, while aligning with global sustainability goals.

Covalent conjugation of Inca peanut albumin and polyphenols with different phenolic hydroxyl numbers through laccase catalysis to improve functional properties

BACKGROUND

Enzymatic crosslinking is a method that can be used to modify Inca peanut albumin (IPA) using polyphenols, and provides desirable functionalities; however, the effect of polyphenol structures on conjugate properties is unclear. In this study, we selected four polyphenols with different numbers of phenolic hydroxyl groups [para-hydroxybenzoic acid (HBA), protocatechuic acid (PCA), gallic acid (GA), and epigallocatechin gallate (EGCG)] for covalent modification of IPA by enzymatic crosslinking, and explored the structure-function changes of the IPA-polyphenol conjugates.

RESULTS

Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) analysis showed that laccase successfully promoted covalent crosslinking of IPA with polyphenols, with the order of degree of conjugation as EGCG > GA > PCA > HBA, the IPA-EGCG conjugate showed the highest polyphenol binding equivalents (98.35 g kg-1 protein), and a significant reduction in the content of free amino, sulfhydryl, and tyrosine group. The oxidation of polyphenols by laccase forms quinone or semiquinone radicals that are covalently crosslinked to the reactive groups of IPA, leading to significant changes in the secondary and tertiary structures of IPA, with spherical structures transforming into dense lamellar structures. The 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging ability and emulsification stability of IPA-EGCG conjugates improved by almost 6-fold and 2.7-fold, respectively, compared with those of unmodified IPA.

CONCLUSION

These data suggest that the higher the number of polyphenol hydroxyl groups, the higher the degree of IPA-polyphenol conjugation; additionally, enzymatic crosslinking can significantly improve the functional properties of IPA. © 2024 Society of Chemical Industry.

Isolation, characterization, and cloning of thermostable pullulanase from Geobacillus stearothermophilus ADM-11

This study aimed to identify thermo-stable pullulanase-producing bacteria in soil samples of potato fields and food-producing companies. Pullulan agar medium was used to screen 17 bacterial strains, which were incubated at 65 °C. The isolate with the maximum activity (375U/ml) was selected and recognized as Geobacillus stearothermophilus ADM-11 by morphological, biochemical characterization, and 16S rRNA gene sequencing. The pullulanase production required optimum pH of 7 and temperature of 75 °C, respectively. The electrophoresis of purified pullulanase on SDS-polyacrylamide gel revealed 83 kDa of a molecular weight that is active at 70 °C and pH 7.0. It was also stable at 90 °C but its activity was decreased by 10 % at 100 °C. The action of pullulanase was increased and stabilized by Ca+2 among the metal ions. Beta and gamma-cyclodextrins inhibited enzyme activity while ethylenediaminetetraacetate (EDTA) and phenylmethylsulfonyl fluoride (PMSF) have no significant effect on pullulanase activity. A full-length pullulanase gene was amplified from G. stearothermophilus ADM-11 using genomic DNA 2.1 kb of PCR product which was then purified and ligated in the cloning vector pTZ57R using the TA cloning technique. Colony PCR confirmed cloning on the positive clones after the pullulanase gene had been ligated and subjected to restriction digestion. It revealed 74 % similarity with the reported pullulanase gene from Geobacillus sp. 44C. The thermostability of pullulanase and its ability to degrade raw pullulan may therefore have wide-scale applications in starch processing, the detergent business, and new biotechnological applications.

Phenolic acid-chitosan derivatives: An effective strategy to cope with food preservation problems

Chitosan, a cost-effective and eco-friendly natural polymeric material, possesses excellent film-forming properties. However, it has low solubility and biological activity, which hinders its widespread applications. To overcome these limitations, researchers have developed phenolic acid-chitosan derivatives that greatly enhance the mechanical, antibacterial and antioxidant properties of chitosan, expanding its potential application, particularly in food preservation. This review aims to provide an in-depth understanding of the structure and biological activity of chitosan and phenolic acid, as well as various synthetic techniques employed in their modification. Phenolic acid-chitosan derivatives exhibit improved physicochemical properties, such as enhanced water solubility, thermal stability, rheological properties, and crystallinity, through grafting techniques. Moreover, these derivatives demonstrate significantly enhanced antibacterial and antioxidant activities. Through graft modification, phenolic acid-chitosan derivatives offer promising applications in food preservation for diverse food products, including fruits, vegetables, meat, and aquatic products. Their ability to improve the preservation and quality of these food items makes them an appealing option for the food industry. This review intends to provide a deeper understanding of phenolic acid-chitosan derivatives by delving into their synthetic technology, characterization, and application in the realm of food preservation.

Effect of a Bacterial Laccase on the Quality and Micro-Structure of Whole Wheat Bread

The gluten protein content in whole-wheat flour is low, which affects the elasticity and viscosity of the dough. Enzymatic modification of the protein may result in a network that mimics gluten, which plays an important role in the processing of whole-wheat foods. In this study, the effects of Halomonas alkaliantartica laccase (LacHa) on the quality parameters of whole-wheat bread were investigated. The optimum dosage of LacHa was 4 U/100 g of whole-wheat flour. At this dosage, whole-wheat bread exhibited the best specific volume and optimum texture parameters. Laccase also extended the storage duration of whole-wheat bread. We analyzed the micro-structure of the dough to determine its gluten-free protein extractable rate and free sulfhydryl group content, and verify that LacHa mediates cross-linking of gluten-free proteins. The results demonstrated that the cross-linking of gluten-free protein by LacHa improves the texture of whole-wheat bread. As a flour improver, LacHa has great developmental and application potential in baked-food production.

Enzymatic post-treatment of ozonation: laccase-mediated removal of the by-products of acetaminophen ozonation

Ozonation is a powerful technique to remove micropollutants from wastewater. As chemical oxidation of wastewater comes with the formation of varying, possibly persistent and toxic by-products, post-treatment of the ozonated effluent is routinely suggested. This study explored an enzymatic treatment of ozonation products using the laccase from Trametes versicolor. A high-performance liquid chromatography coupled with high-resolution mass spectrometry (HPLC-HRMS) analysis revealed that the major by-products were effectively degraded by the enzymatic post-treatment. The enzymatic removal of the by-products reduced the ecotoxicity of the ozonation effluent, as monitored by the inhibition of Aliivibrio fischeri. The ecotoxicity was more effectively reduced by enzymatic post-oxidation at pH 7 than at the activity maximum of the laccase at pH 5. A mechanistic HPLC-HRMS and UV/Vis spectroscopic analysis revealed that acidic conditions favored rapid conversion of the phenolic by-products to dead-end products in the absence of nucleophiles. In contrast, the polymerization to harmless insoluble polymers was favored at neutral conditions. Hence, coupling ozonation with laccase-catalyzed post-oxidation at neutral conditions, which are present in wastewater effluents, is suggested as a new resource-efficient method to remove persistent micropollutants while excluding the emission of potentially harmful by-products.

Applications and immobilization strategies of the copper-centred laccase enzyme; a review

Laccase is a multi-copper enzyme widely expressed in fungi, higher plants, and bacteria which facilitates the direct reduction of molecular oxygen to water (without hydrogen peroxide production) accompanied by the oxidation of an electron donor. Laccase has attracted attention in biotechnological applications due to its non-specificity and use of molecular oxygen as secondary substrate. This review discusses different applications of laccase in various sectors of food, paper and pulp, waste water treatment, pharmaceuticals, sensors, and fuel cells. Despite the many advantages of laccase, challenges such as high cost due to its non-reusability, instability in harsh environmental conditions, and proteolysis are often encountered in its application. One of the approaches used to minimize these challenges is immobilization. The various methods used to immobilize laccase and the different supports used are further extensively discussed in this review.

Gelation profile of laccase-crosslinked Bambara groundnut (Vigna subterranea) protein isolate

Enzymatic crosslinking has gained attention in improving plant protein heat-induced gels, which are composed of weak network structures. The aim of the study was to investigate the effect of laccase crosslinking on the rheological and microstructural properties of heat-induced Bambara groundnut protein gels. The rheological properties of laccase-modified Bambara groundnut protein isolate (BPI¹) gel formed in situ were investigated. Changes in viscoelastic properties were monitored during heating and cooling ramps and gel structure fingerprints were analyzed by frequency sweep. Laccase addition induced an initial protein structure breakdown (G″>G') at an enzyme dose-dependent (1-3 U/g) before gel formation and stabilization. Gel point temperatures were significantly decreased from 85°C to 29°C (∼3 folds) with increasing laccase activity (0 to 3 U/g protein, respectively). For laccase crosslinked gels, G' was substantially greater than G" (>1 log) with no dependency on angular frequency, which suggests the formation of relatively well-structured gels. The highest gel strength (tan δ of 0.09, G* of 555.51 kPa & An of 468.04 kPa) was recorded at a laccase activity of 2 U/g protein and the gels formed at this activity appeared homogeneous with compact lath sheet-like structure. The crosslinking effects of laccase were corroborated by the decrease in thiol and phenolic contents as well as the crosslinking of amino acids in model reactions. Overall, the use of laccase improved gel properties and significantly altered the gelation profile of BPI. Laccase-modified Bambara groundnut protein gels have potential to be used in food texture improvement and development of new food products. For instance, they can be used in plant-based milk products such as yoghurt and cheese.

Enhancement of Antioxidant Property of N-Carboxymethyl Chitosan and Its Application in Strawberry Preservation

Bio-enzymatic grafting phenolic acid to chitosan derivative is an efficient and environmentally friendly molecular synthesis technology. In the present study, N-carboxymethyl chitosan (CMCS) was grafted with gallic acid (GA) using recombinant bacterial laccase from Streptomyces coelicolor as a catalyst. GA and CMCS were successfully grafted as determined by measuring amino acid content, Fourier transform infrared (FTIR) spectroscopy and ultraviolet-visible (UV-Vis) spectroscopy. Then, the effect of GA-g-CMCS coating on the freshness of strawberries at 20 ± 2 °C was explored. The physiological and biochemical quality indicators of strawberries during storage were monitored. The 1.5% GA-g-CMCS coating helped to protect the antioxidant properties and nutrients of strawberries and extend the shelf life. Specifically, it reduced the weight loss of strawberries during preservation (originally 12.7%) to 8.4%, maintained titratable acidity content (TA) residuals above 60% and reduced decay rate from 36.7% to 8.9%. As a bioactive compound, GA-g-CMCS has the potential to become an emerging food packing method. These results provide a theoretical basis and reference method for the subsequent synthesis and application of CMCS derivatives.

Corn Cob as a Green Support for Laccase Immobilization-Application on Decolorization of Remazol Brilliant Blue R

The high demand for food and energy imposed by the increased life expectancy of the population has driven agricultural activity, which is reflected in the larger quantities of agro-industrial waste generated, and requires new forms of use. Brazil has the greatest biodiversity in the world, where corn is one of the main agricultural genres, and where over 40% of the waste generated is from cobs without an efficient destination. With the aim of the valorization of these residues, we proposed to study the immobilization of laccase from Aspergillus spp. (L_Asp) in residual corn cob and its application in the degradation of Remazol Brilliant Blue R (RBBR) dye. The highest yields in immobilized protein (75%) and residual activity (40%) were obtained at pH 7.0 and an enzyme concentration of 0.1 g.mL⁻¹, whose expressed enzyme activity was 1854 U.kg⁻¹. At a temperature of 60 °C, more than 90% of the initial activity present in the immobilized biocatalyst was maintained. The immobilized enzyme showed higher efficiency in the degradation (64%) of RBBR dye in 48 h, with improvement in the process in 72 h (75%). The new biocatalyst showed operational efficiency during three cycles, and a higher degradation rate than the free enzyme, making it a competitive biocatalyst and amenable to industrial applications.

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.

Green production of a yellow laccase by Coriolopsis gallica for phenolic pollutants removal

As a group of green biocatalysts, fungal laccases have aroused great interest in diverse biotechnological fields. Therein, yellow laccase has advantages over blue laccase in catalytic performance, but it is not common in the reported fungal laccases. Here, we report a yellow laccase from white-rot fungus Coriolopsis gallica NCULAC F1 about its production, purification, characterization, and application. Laccase production in the co-fermentation of pomelo peel and wheat bran reached the enzyme activity by 10,690 U/L after 5 days with a 13.58-time increase. After three steps of purification, laccase increased the specific activity from 30.78 to 188.79 U/mg protein with an activity recovery of 45.64%. The purified C. gallica laccase (CGLac) showed a molecular mass of about 57 kDa. CGLac had a yellow color and no absorption peaks at 610 nm and 330 nm, suggesting that it’s a yellow laccase. CGLac exhibited stability towards temperature (40–60 °C) and neutral pH (6.0–8.0). Fe³⁺ and Mn²⁺ strongly stimulated CGLac activity by 162.56% and 226.05%, respectively. CGLac remained high activities when exposed to organic reagents and putative inhibitors. Additionally, CGLac contributed to 90.78%, 93.26%, and 99.66% removal of phenol, p-chlorophenol and bisphenol A after 120 min, respectively. In conclusion, a green efficient production strategy was introduced for fungal laccase, and the obtained CGLac presented great enzymatic properties and catalytic potential in the removal of phenolic pollutants.

Pomelo peels and wheat bran are great nutritional sources and laccase inducers.

CGLac showed the spectral characteristic of yellow laccase.

CGLac had great stability and catalytic ability for phenolic pollutants removal.

Enzymatic synthesis, characterization and properties of the protein-polysaccharide conjugate: A review

Poor solubility of proteins negatively affects their functional properties and greatly limits their application. Enzymatic cross-linking with polysaccharides can improve solubility and functional properties of proteins. The enzymes used include transglutaminase, laccase and peroxidase. Therefore, this work introduces the cross-linking mechanisms of these enzymes and the characterization techniques, the improved properties and the potential applications of the enzymatically-synthesized protein-polysaccharide conjugate. Transglutaminase catalyzes the formation of a new peptide bond and thus works on amino-containing polysaccharides to conjugate with proteins. However, laccase and peroxidase catalyze oxidation of various compounds with phenol and aniline structures. Therefore, these two enzymes can catalyze the conjugate reaction between proteins and feruloylated polysaccharides which are widely distributed in cereal bran. Compared with the unmodified protein, the enzymatically-synthesized protein-polysaccharide conjugate usually has higher solubility and better functional properties. Thus, it is inferred that enzymatic conjugation with polysaccharide molecules can extend the application of proteins.

Laccases—Versatile Enzymes Used to Reduce Environmental Pollution

The accumulation of waste and toxic compounds has become increasingly harmful to the environment and human health. In this context, the use of laccases has become a focus of interest, due to the properties of these versatile enzymes: low substrate specificity, and water formation as a non-toxic end product. Thus, we begin our study with a general overview of the importance of laccase for the environment and industry, starting with the sources of laccases (plant, bacterial and fungal laccases), the structure and mechanism of laccases, microbial biosynthesis, and the immobilization of laccases. Then, we continue with an overview of agro-waste treatment by laccases wherein we observe the importance of laccases for the biodisponibilization of substrates and the biodegradation of agro-industrial byproducts; we then show some aspects regarding the degradation of xenobiotic compounds, dyes, and pharmaceutical products. The objective of this research is to emphasize and fully investigate the effects of laccase action on the decomposition of lignocellulosic materials and on the removal of harmful compounds from soil and water, in order to provide a sustainable solution to reducing environmental pollution.

Oxidation of Various Kraft Lignins with a Bacterial Laccase Enzyme

Modification of kraft lignin (KL), traditionally uses harsh and energy-demanding physical and chemical processes. In this study, the potential of the bacterial laccase CotA (spore coating protein A) for oxidation of KL under mild conditions was assessed. Thereby, the efficiency of CotA to oxidize both softwood and hardwood KL of varying purity at alkaline conditions was examined. For the respective type of wood, the highest oxidation activity by CotA was determined for the medium ash content softwood KL (MA_S) and the medium ash content hardwood KL (MA_H), respectively. By an up to 95% decrease in fluorescence and up to 65% in phenol content coupling of the structural lignin units was indicated. These results correlated with an increase in viscosity and molecular weight, which increased nearly 2 and 20-fold for MA_H and about 1.3 and 6.0-fold for MA_S, respectively. Thus, this study confirms that the CotA laccase can oxidize a variety of KL at alkaline conditions, while the origin and purity of KL were found to have a major impact on the efficiency of oxidation. Under the herein tested conditions, it was observed that the MA_H KL showed the highest susceptibility to CotA oxidation when compared to the other hardwood KLs and the softwood KLs. Therefore, this could be a viable method to produce sustainable resins and adhesives.

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.

Enzymatic Functionalization of Wood as an Antifouling Strategy against the Marine Bacterium Cobetia marina

The protection of wood in marine environments is a major challenge due to the high sensitivity of wood to both water and marine microorganisms. Besides, the environmental regulations are pushing the industry to develop novel effective and environmentally friendly treatments to protect wood in marine environments. The present study focused on the development of a new green methodology based on the laccase-assisted grafting of lauryl gallate (LG) onto wood to improve its marine antifouling properties. Initially, the enzymatic treatment conditions (laccase dose, time of reaction, LG concentration) and the effect of the wood specie (beech, pine, and eucalyptus) were assessed by water contact angle (WCA) measurements. The surface properties of the enzymatically modified wood veneers were assessed by X-ray photoelectron spectroscopy (XPS), Fourier transform-infrared spectroscopy (FTIR). Antifouling properties of the functionalized wood veneers against marine bacterium Cobetia marina were studied by scanning electron microscopy (SEM) and protein measurements. XPS and FTIR analysis suggested the stable grafting of LG onto the surface of wood veneers after laccase-assisted treatment. WCA measurements showed that the hydrophobicity of the wood veneers significantly increased after the enzymatic treatment. Protein measurements and SEM pictures showed that enzymatically-hydrophobized wood veneers modified the pattern of bacterial attachment and remarkably reduced the bacterium colonization. Thus, the results observed in the present study confirmed the potential efficiency of laccase-assisted treatments to improve the marine antifouling properties of wood.

Biodegradation of sulfonamide antibiotics through the heterologous expression of laccases from bacteria and investigation of their potential degradation pathways

In this study, seven laccase genes from different bacteria were linked with the signal peptides PelB, Lpp or Ompa for heterologous expression in E. coli. The recombinant strains were applied for the removal of sulfadiazine (SDZ), sulfamethazine (SMZ), and sulfamethoxazole (SMX). The results obtained for different signal peptides did not provide insights into the removal mechanism. The removal ratios of SDZ, SMZ, and SMX obtained with the recombinant strain 6#P at 60 h were around 92.0%, 89.0%, and 88.0%, respectively. The degradation pathways of sulfonamides have been proposed, including SO₂ elimination, hydroxylation, oxidation, pyrimidine ring cleavage, and N-S bond cleavage. Different mediators participate in the degradation of antibiotics through different mechanisms, and different antibiotics have different responses to the same mediator. The addition of 2,2'-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) slightly promoted the removal of sulfonamides by most recombinant strains with different signal peptides, especially for the recombinant strain 2#O. The removal of sulfonamides by 1-hydroxybenzotriazole (HBT) varied with the recombinant strains. Syringaldehyde (SA) had a slight inhibitory effect on the removal of sulfonamides, with the most significant effect on strains 7#L and 7#O.

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.

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.

Enzymatic treatment of phenolic pollutants by a small laccase immobilized on APTES-functionalised magnetic nanoparticles

In this study, we have successfully synthesized magnetic nanoparticles (MNPs), functionalised them by silanization and used them for the covalent immobilization of a recombinant small laccase (rSLAC) from Streptomyces coelicolor. The immobilized recombinant laccase (MNP-rSLAC) was subsequently used for the treatment of phenol, 4-chlorophenol (4-CP) and 4-fluorophenol (4-FP). The enzyme completely degraded 80 µg/mL of the selected phenolic compounds within 2 h in the presence of a natural mediator, acetosyringone. The MNP-rSLAC retained > 73% of initial activity (2,6-dimethoxyphenol as substrate) after 10 catalytic cycles and could be easily recovered from the reaction mixture by the application of magnetic field. Furthermore, immobilised rSLAC exhibited better storage stability than its free counterpart. The Michaelis constant (K_m) value for the immobilised rSLAC was higher than free rSLAC, however the maximum velocity (V_max) of the immobilised SLAC was similar to that of the free rSLAC. Growth inhibition studies using Escherichia coli showed that rSLAC-mediated treatment of phenolic compounds reduced the toxicity of phenol, 4-CP and 4-FP by 90, 60 and 55%, respectively. Interestingly, the presence of selected metal ions (Co²⁺, Cu²⁺, Mn²⁺) greatly enhanced the catalytic activity of rSLAC and MNP-rSLAC. This study indicates that immobilized small laccase (MNP-rSLAC) has potential for treating wastewater contaminated with phenolic compounds.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-02854-0.

Advances in laccase-triggered anabolism for biotechnology applications

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

Chitosan grafting via one-enzyme double catalysis: An effective approach for improving performance of wool

Chitosan is considered as a green additive with broad application prospects due to its advantages like biodegradability and antibacterial ability. Herein, we proposed an effective chitosan grafting approach via "one-enzyme double catalysis" strategy which aimed at functionalizing wool fibers to achieve bidirectionally multiple covalent crosslinking between chitosan and wool by laccase/2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) mediated oxidization. The mechanism was studied using models of wool and chitosan in terms of UV, FTIR, GPC and MALDI-TOF MS. Meanwhile, the structure and morphology of wool fiber grafted with chitosan were characterized by ATR-FTIR and SEM. Compared with untreated wool, this efficient method can significantly improve the dimensional stability to felting (2.53 %), wettability and dyeability of wool fabric, and can also compensate for the strength loss caused by the pretreatment. The present work provides a useful path for the enzymatic modification of keratin-containing fibers like wool using chitosan and other natural biopolymers with similar structure.

Recent environmental applications of and development prospects for immobilized laccase: a review

Laccases have enormous potential as promising 'green' biocatalysts in environmental applications including wastewater treatment and polluted soil bioremediation. The catalytic oxidation reaction they perform uses only molecular oxygen without other cofactors, and the only product after the reaction is water. The immobilization of laccase offers several improvements such as protected activity and enhanced stability over free laccase. In addition, the reusability of immobilized laccase is adistinct advantage for future applications. This review covers the sources of and progress in laccase research, and discusses the different methodologies of laccase immobilization that have emerged in the recent 5-10 years, as well as its applications to environmental fields, and evaluates these emerging technologies. Abbreviations: (2,4,6-TCP): 2,4,6-trichlorophenol; (2,4-DCP): 2,4-dichlorophenol; (ABTS), 2,2-azinobis (3-ethylbenzothiazoline-6-sulfonic acid); (ACE), acetaminophen; (BC-AS), almond shell; (BC-PM), pig manure; (BC-PW), pine wood; (BPA), bisphenol A; (BPA), bisphenol A; (BPF), bisphenol F; (BPS), bisphenol S; (C₆₀), fullerene; (Ca-AIL), calcium-alginate immobilized laccase; (CBZ), carbamazepine; (CETY), cetirizine; (CHT-PGMA-PEI-Cu (II) NPs), Cu (II)-chelated chitosan nanoparticles; (CLEAs), cross-linked enzyme aggregates; (CMMC), carbon-based mesoporous magnetic composites; (COD), chemical oxygen demand; (CPH), ciprofloxacin hydrochloride; (CS), chitosan; (CTC), chlortetracycline; (Cu-AIL), copper-alginate immobilized laccase; (DBR K-4BL), Drimarene brilliant red K-4BL; (DCF), diclofenac; (E1),estrone; (E2), 17 β-estradiol; (EDC), 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride; (EDCs), endocrine disrupting chemicals; (EE2), 17α-ethinylestradiol; (EFMs), electrospun fibrous membranes; (FL), free laccase; (fsMP), fumed silica microparticles; (GA-CBs), GLU-crosslinked chitosan beads; (GA-CBs), glutaraldehyde-crosslinked chitosan beads; (GA-Zr-MOF), graphene aerogel-zirconium-metal organic framework; (GLU), glutaraldehyde; (GO), graphene oxide; (HMCs), hollow mesoporous carbon spheres; (HPEI/PES), hyperbranched polyethyleneimine/polyether sulfone; (IC), indigo carmine; (IL), immobilized laccase; (k_cat), catalytic constant; (K_m), Michealis constant; (M-CLEAs), Magnetic cross-linked enzyme aggregates; (MMSNPs-CPTS-IDA-Cu²⁺), Cu²⁺-chelated magnetic mesoporous silica nanoparticles; (MSS), magnetic mesoporous silica spheres; (MWNTs), multi-walled carbon nanotubes; (MWNTs), multi-walled carbon nanotubes; (NHS), N-hydroxy succinimide; (O-MWNTs), oxidized-MWNTs; (P(AAm-NIPA)), poly(acrylamide-N-isopropylacrylamide); (p(GMA)), poly(glycidyl methacrylate); (p(HEMA)), poly(hydroxyethyl methacrylate); (p(HEMA-g-GMA)-NH₂, poly(glycidyl methacrylate) brush grafted poly(hydroxyethyl methacrylate); (PA6/CHIT), polyamide 6/chitosan; (PAC), powdered active carbon; (PAHs), polycyclic aromatic hydrocarbons; (PAM-CTS), chitosan grafted polyacrylamide hydrogel; (PAN/MMT/GO), polyacrylonitrile/montmorillonite/graphene oxide; (PAN/PVdF), polyacrylonitrile/polyvinylidene fluoride; (PEG), poly ethylene glycol; (PEI), Poly(ethyleneimine); (poly(4-VP)), poly(4-vinyl pyridine); (poly(GMA-MAA)), poly(glycidyl methacrylate-methacrylic acid); (PVA), polyvinyl alcohol; (RBBR), Remazol Brilliant Blue R; (SDE), simulated dye effluent; (semi-IPNs), semi-interpenetrating polymer networks; (TC), tetracycline; (TCH), tetracycline hydrochloride; (TCS), triclosan; (Vmax), maximum activity; (Zr-MOF, MMU), micro-mesoporous Zr-metal organic framework.

Kinetics and reaction pathways for the transformation of 4-tert-butylphenol by ferrate(VI)

4-tert-butylphenol (4-tBP) is a phenolic endocrine disrupting chemical that has attracted great attention due to its wide occurrence, environmental persistence, and possible toxic effects. In this study, we systematically investigated the transformation of 4-tBP in ferrate (VI) oxidation process. The second-order reaction rate constant (k_app) of Fe(VI) with 4-tBP decreases with solution pH, and the k_app value was determined as 295 M^-1·s^-1 at pH 8.0. The removal efficiency of 4-tBP was slightly decreased by Mg²⁺ and HCO₃^-, while accelerated at varying degrees by the presence of Cu²⁺ and humic acid. Product analysis revealed that 4-tBP was mainly transformed into hydroxylation products, benzene-ring cleavage products, dimers and higher polymerization products via oxygen atom transfer, ring-opening of the benzene ring and radical coupling reaction. Furthermore, initial reactions of 4-tBP were rationalized by theoretical analysis of atom partial charges, frontier electron densities, and spin densities. Nearly complete removal of 4-tBP (20 μM) was achieved after 5 min of reaction in both ultrapure water and natural waters, demonstrating the feasibility of this Fe(VI) oxidation method in treating phenols-contaminated waters.

KMnO4-mediated reactions for hexachlorophene in aqueous solutions: Direct oxidation, self-coupling, and cross-coupling

Hexachlorophene (HCP) is used in a range of general cleaning and disinfecting products and has received increased attention due to its damaging effect to the central nervous system in animals and its toxicity in humans. The chemical oxidation of HCP by KMnO₄ was performed to systematically evaluate the effects of oxidant dose, pH, temperature, typical anions, humic acid (HA), and various matrices on HCP removal. The second-order rate constant for HCP was determined to be 4.83 × 10⁴ M^-1 s^-1 at pH 7.0 and 25 °C. The presence of HA can inhibit the removal of HCP by KMnO₄, while Cl^-, NO₃^-, SO₄^2-, PO₄^3-, and CO₃^2- have negligible effects. Degradation products analysis of the reaction, as well as theoretical calculations of HCP molecule and its phenoxy radical species, indicated that KMnO₄ oxidation for HCP included a C-C bridge bond cleavage, hydroxylation, direct oxidation and self-coupling, and cross-coupling reactions. This study revealed that KMnO₄ oxidation is an effective technique for eliminating HCP in real water and wastewater.

Influence of humic acids on fungal laccase-initiated 17α-ethynylestradiol oligomerization: Transformation kinetics and products distribution

Fungal laccase has aroused great concern in rapidly removing estrogens because of its ability to accelerate humification and oligomerization. Here, the effect of two humic acids (HAs) on the reaction kinetics and products distribution of 17α-ethynylestradiol (EE2) in laccase-initiated humification and coupling was systematically elucidated. Laccase from Trametes versicolor exhibited over 98.3% removal rate for EE2 at pH 5.0 within 120 min, while HAs invariably restrained EE2 transformation by competing with target-substrate for the enzymatic catalytic center. EE2 removal followed pseudo-first-order kinetics, and the rate constant was decreased markedly with increasing concentration of two HAs (0-60 mg L^-1). Additionally, laccase heightened the aromaticity and humification degrees (A_{250 nm}/A_{365 nm} ratio) of HAs probably due to the formation of new humic polymers such as (HA)_m and/or (HA)_m-(EE2)_n (m and n represent the number of HA and EE2 units, respectively). Three major EE2 oligomers were identified, in accordance with a mechanism involving the phenoxy radical-driven polymerization to yield a wide variety of self-coupling products. Notably, HAs diminished the extent of EE2 self-coupling but aggrandized the cross-coupling between EE2 and HAs, and the inhibition degree of EE2 self-coupling increased with the concentration of HAs. One major reason is EE2 could be covalently incorporated into humic molecules to produce (HA)_m-(EE2)_n cross-coupling products via radical-caused C-C, C-O-C, and/or C-O-C bonds, thereby reducing EE2 self-oligomerization. These findings highlight that HAs play a vital role in the fungal laccase-induced humification and oligomerization of EE2, which obviously alter the geochemical fate and transport of EE2 in natural aquatic ecosystems.

The functionality of laccase- or peroxidase-treated potato flour: Role of interactions between protein and protein/starch

Potato flour is used in bakery products, extruded products and snacks. However, it displays weaker gel strengths and thus the wholesome utility is curtailed significantly. To improve viscoelastic properties and stability of potato gels, herein potato flour was treated with laccase and peroxidase to create a protein network structure leading to stable gels. The results revealed that the secondary structure of potato proteins altered upon the enzyme treatment. The gels of peroxidase-treated potato flour (PPF) and laccase-treated potato flour (LPF) displayed larger anti-shear ability, thermal stability and stronger three-dimensional network structure compared to the native potato gel. The PPF and LPF gels exhibited stronger viscoelastic properties and structural stability compared to peroxidase-treated potato protein and laccase-treated potato protein gels. The outcome serves as a theoretical basis to improve the properties of potato gels and to promote the designing and the development of novel potato flour based functional food.

Enhanced Physicochemical Stability of β-Carotene Emulsions Stabilized by β-Lactoglobulin-Ferulic Acid-Chitosan Ternary Conjugate

The purpose of the present work is to fabricate emulsions with excellent stability to deliver β-carotene using a novel biomacromolecule. β-Lactoglobulin-ferulic acid-chitosan ternary conjugate (BFCC), which was synthesized based on the carbodiimide-mediated coupling reaction and laccase induction, was confirmed by Fourier transform infrared (FTIR) and proton nuclear magnetic resonance (¹H NMR) spectra. Also, BFCC was used to stabilize β-carotene emulsions. The results indicated that the concentration of BFCC affected the physical stability of β-carotene emulsions. Compared with the emulsions stabilized by β-lactoglobulin (β-LG), chitosan-ferulic acid conjugate (CFC), and β-LG-CFC mixture (BFCM), the emulsion stabilized by BFCC exhibited better stability under various environmental stresses. Moreover, the emulsion stabilized by BFCC had higher β-carotene retention during storage at 25 and 55 °C or under ultraviolet (UV) light exposure. The knowledge acquired in the current research offered an effective way to develop novel biomacromolecular emulsifiers and could find potential in fabricating delivery systems for bioactive compounds with markedly enhanced physiochemical properties.

Evolution and stabilization of environmental persistent free radicals during the decomposition of lignin by laccase

Soil microbial enzymes may induce lignin decomposition, accompanied by generation of free radicals. The evolution of environmentally persistent free radicals (EPFRs) and reactive oxygen species (ROS) during laccase-catalyzed lignin decomposition remains unclear. Characterization by electron paramagnetic resonance spectroscopy revealed gradually increased concentration of EPFRs, with maximum levels within 6 h that remained constant, accompanied by the increase in g-factor from 2.0037 to 2.0041. The results suggested the generation of oxygen-centered radicals on lignin. The EPFRs produced on solid samples slowly decreased by 17.2% over 17 d. ROS were also detected to have a similar trend as that of the evolution of EPFRs. Scanning electron microscopy, attenuated total reflectance-Fourier transform infrared spectroscopy, gel permeation chromatography and nuclear magnetic resonance analyses suggested the demethylation and oxidation of lignin. We clarify the biogeochemical transformation of lignin and potential contributions to the generation of EPFRs and ROS in soil.