A novel homodimer laccase from Cerrena unicolor BBP6: Purification, characterization, and potential in dye decolorization and denim bleaching

Optimizing laccase selection for enhanced outcomes: a comprehensive review

Despite their widespread applications in sectors such as pulp and paper, textile, food and beverage, pharmaceuticals, and biofuel production, laccases encounter challenges related to their activity and stability under varying reaction conditions. This review accumulates data on the complex interplay between laccase characteristics and reaction conditions for maximizing their efficacy in diverse biotechnological processes. Benefits of organic media such as improved substrate selectivity and reaction control, and their risks such as enzyme denaturation and reduced activity are reported. Additionally, the effect of reaction conditions such as pH and temperature on laccase activity and stability are gathered and reported. Sources like Bacillus pumilus, Alcaligenes faecalis, Bacillus clausii, and Bacillus tequilensis SN4 are producing laccases that are both thermo-active and alkali-active. Additionally, changes induced by the presence of various substances within reaction media such as metals, inhibitors, and organic solvents are also reported. Bacillus pumilus and Bacillus licheniformis LS04 produce the most resistant laccases in this case. Finally, the remarkable laccases have been highlighted and the proper laccase source for each industrial application is suggested.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-024-04015-5.

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.

Application of enzymes for an eco-friendly approach to textile processing

Textile industry is one of the oldest industries existing from several centuries. Major concern of the industry is to design, produce, and distribute yarn, cloth, and clothing. Diverse physical and chemical operations are required in order to achieve this. Environmental concerns related to textile industry have attained attention all around the world as it is generating large amounts of effluents having various toxic agents and chemicals. Enzymes have been suggested as the best possible alternative to replace or reduce these hazardous and toxic chemicals. Enzymes like amylase, cellulase, catalase, protease, pectinase, laccase, and lipase have widely been used in textile manufacturing processes. Use of enzymatic approach is very promising as they are eco-friendly, produce high-quality products, and lead to the reduction of energy, water, and time. This review highlights the significance of different enzymes employed in the textile industry at various stages along with the conventional textile processing.

Lignocellulolytic Biocatalysts: The Main Players Involved in Multiple Biotechnological Processes for Biomass Valorization

Human population growth, industrialization, and globalization have caused several pressures on the planet's natural resources, culminating in the severe climate and environmental crisis which we are facing. Aiming to remedy and mitigate the impact of human activities on the environment, the use of lignocellulolytic enzymes for biofuel production, food, bioremediation, and other various industries, is presented as a more sustainable alternative. These enzymes are characterized as a group of enzymes capable of breaking down lignocellulosic biomass into its different monomer units, making it accessible for bioconversion into various products and applications in the most diverse industries. Among all the organisms that produce lignocellulolytic enzymes, microorganisms are seen as the primary sources for obtaining them. Therefore, this review proposes to discuss the fundamental aspects of the enzymes forming lignocellulolytic systems and the main microorganisms used to obtain them. In addition, different possible industrial applications for these enzymes will be discussed, as well as information about their production modes and considerations about recent advances and future perspectives in research in pursuit of expanding lignocellulolytic enzyme uses at an industrial scale.

Degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) by fungi originating from Vietnam

Three different fungi were tested for their ability to degrade 2,4-dichlorophenoxyacetic acid and 2,4,5-trichlorophenoxyacetic acid and for the role of laccases and cytochromes P450-type in this process. We studied a white-rot fungus Rigidoporus sp. FMD21, which has a high laccase activity, for its efficiency to degrade these herbicides. A positive correlation was found between its laccase activity and the corresponding herbicide degradation rate. Even more, the doubling of the enzyme activity in this phase corresponded with a doubling of the herbicide degradation rate. It is, therefore, tempting to speculate that laccase is the most dominant enzyme in the degradation of 2,4-D and 2,4,5-T under these conditions. In addition, it was shown that Rigidoporus sp. FMD21 partly relies on cytochromes P450-type for the breakdown of the herbicides as well. Two filamentous fungi were isolated from soil contaminated with herbicides and dioxins located at Bien Hoa airbase. They belong to genera Fusarium and Verticillium of the phylum Ascomycota as judged by their 18S rRNA gene sequences. Both isolated fungi were able to degrade the herbicides but with different rates. Their laccase activity, however, was very low and did not correlate with the rate of breakdown of the herbicides. These data indicate that the white-rot fungus most likely synthesizes laccase and cytochromes P450-type for the breakdown of the herbicides, while the types of enzyme used for the breakdown of the herbicides by the two Ascomycota remain unclear.

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.

Genomic Studies of White-Rot Fungus Cerrena unicolor SP02 Provide Insights into Food Safety Value-Added Utilization of Non-Food Lignocellulosic Biomass

Cerrena unicolor is an ecologically and biotechnologically important wood-degrading basidiomycete with high lignocellulose degrading ability. Biological and genetic investigations are limited in the Cerrena genus and, thus, hinder genetic modification and commercial use. The aim of the present study was to provide a global understanding through genomic and experimental research about lignocellulosic biomass utilization by Cerrena unicolor. In this study, we reported the genome sequence of C. unicolor SP02 by using the Illumina and PacBio 20 platforms to obtain trustworthy assembly and annotation. This is the combinational 2nd and 3rd genome sequencing and assembly of C. unicolor species. The generated genome was 42.79 Mb in size with an N50 contig size of 2.48 Mb, a G + C content of 47.43%, and encoding of 12,277 predicted genes. The genes encoding various lignocellulolytic enzymes including laccase, lignin peroxidase, manganese peroxidase, cytochromes P450, cellulase, xylanase, α-amylase, and pectinase involved in the degradation of lignin, cellulose, xylan, starch, pectin, and chitin that showed the C. unicolor SP02 potentially have a wide range of applications in lignocellulosic biomass conversion. Genome-scale metabolic analysis opened up a valuable resource for a better understanding of carbohydrate-active enzymes (CAZymes) and oxidoreductases that provide insights into the genetic basis and molecular mechanisms for lignocellulosic degradation. The C. unicolor SP02 model can be used for the development of efficient microbial cell factories in lignocellulosic industries. The understanding of the genetic material of C. unicolor SP02 coding for the lignocellulolytic enzymes will significantly benefit us in genetic manipulation, site-directed mutagenesis, and industrial biotechnology.

Evaluation of Laccase Activities by Three Newly Isolated Fungal Species in Submerged Fermentation With Single or Mixed Lignocellulosic Wastes

Three newly isolated fungal species, namely, Cerrena unicolor Han 849, Lenzites betulina Han 851, and Schizophyllum commune Han 881, isolated from their native habitats in Wulingshan National Nature Reserve of Hebei Province of northern China, were screened for laccase production with single or mixed lignocellulosic wastes. C. unicolor Han 849 was found to express the highest levels of laccase with single or mixed lignocellulosic wastes compared with L. betulina Han 851 and S. commune Han 881. The highest laccase activity from the mixed fungal culture of C. unicolor Han 849 and S. commune Han 881 or L. betulina Han 851 on Firmiana platanifolia was 1,373.12 ± 55.93 and 1,144.85 ± 34.97 U/L, respectively, higher than that from other tested conditions. L. betulina Han 851 or S. commune Han 881 mixed with other species was also helpful for accelerating laccase secretion due to reach maximum enzyme activity quickly. The treatment of mixing different species, including the mixture of two or three species, was obviously conducive to the improvement of laccase activity on Firmiana platanifolia. These results revealed that the fungal co-culture and the mixed lignocellulosic wastes contribute to the improvement of laccase activities and enhance laccase activities within a short period. These findings would be helpful for providing a new method for rapid production of low-cost laccase and for optimization of integrated industrial laccase production.

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

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

Sustainable Denim Bleaching by a Novel Thermostable Bacterial Laccase

Laccases have emerged as environment-friendly multifaceted biocatalysts for diverse biotechnological applications. Here, we isolated a high molecular weight (88 kDa) extremophilic laccase (LacT) from Brevibacillus agri, with the aim to exploit its extreme characters in denim bleaching. LacT has been characterized as a thermostable, acidophilic enzyme with high salt, organic solvent, and divalent metal tolerance properties. Denim bleaching efficiency of LacT was optimum at pH 4.0 and appeared to be surpassing over other reported laccases. LacT also exhibited remarkable efficacy in the decolorization of water-soluble health hazardous azo-dyes, and thus transpired to be a promising bio-bleaching and dye decolorizing agent.

A New Laccase of Lac 2 from the White Rot Fungus Cerrena unicolor 6884 and Lac 2-Mediated Degradation of Aflatoxin B1

Aflatoxin B₁ (AFB₁) is a known toxic human carcinogen and can be detoxified by laccases, which are multicopper oxidases that convert several environmental pollutants and toxins. In this study, a new laccase that could catalyze AFB₁ degradation was purified and identified from the white-rot fungus Cerrena unicolor 6884. The laccase was purified using (NH₄)₂SO₄ precipitation and anion exchange chromatography, and then identified as Lac 2 through zymogram and UHPLC-MS/MS based on the Illumina transcriptome analysis of C. unicolor 6884. Six putative laccase protein sequences were obtained via functional annotation. The lac 2 cDNA encoding a full-length protein of 512 amino acids was cloned and sequenced to expand the fungus laccase gene library for AFB₁ detoxification. AFB₁ degradation by Lac 2 was conducted in vitro at pH 7.0 and 45 °C for 24 h. The half-life of AFB₁ degradation catalyzed by Lac 2 was 5.16 h. Acetosyringone (AS), Syrinagaldehyde (SA) and [2,2' -azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid)] (ABTS) at 1 mM concentration seemed to be similar mediators for strongly enhancing AFB₁ degradation by Lac 2. The product of AFB₁ degradation catalyzed by Lac 2 was traced and identified to be Aflatoxin Q₁ (AFQ₁) based on mass spectrometry data. These findings are promising for a possible application of Lac 2 as a new aflatoxin oxidase in degrading AFB₁ present in food and feeds.

Bioprocess optimization of laccase production through solid substrate fermentation using Perenniporia tephropora-L168 and its application in bioremediation of triaryl-methane dye

Laccases are multi copper oxidases that can oxidize both phenolic and nonphenolic lignin related compounds. Consequently, there has been continuous demand for laccases for the oxidative degradation of phenolic dyes in effluents. In view of this, the present work was focused on laccase production by solid substrate fermentation using a newly isolated fungus Perenniporia tephropora-L168. To intensify the laccase production, the process parameters pH, nitrogen, inducer, and substrate: water ratio were optimized by using statistical model. A set of optimal conditions noted were pH 3, nitrogen 0.001 g/L; inducer 0.5% and substrate: water ratio (1:10), which yielded laccase 1,160 U/g. The crude laccase exhibited noteworthy potential to degrade a triaryl-methane dye especially Malachite green. Also, during bioremediation studies, the statistical process optimization could achieve 81% decolourization within 180 min. The laccase treatment brought chemical transformation in malachite green as evident from UV-Visible spectra, FTIR, HPLC while toxicity against bacteria and fungi was also reduced. During phytotoxicity study, effect of treated and untreated dye on germination of seed was analyzed. Interestingly, the germination index for Vigna aconitifolia and Vigna radiata was increased by two and fourfold, respectively. Overall, this work demonstrates optimized production of laccase using Perenniporia tephropora-L168 and its efficient bioremediation potential for triaryl-methane dye.

Optimization of Growth Medium and Fermentation Conditions for the Production of Laccase3 from Cryphonectria parasitica Using Recombinant Saccharomyces cerevisiae

Statistical experimental methods were used to optimize the medium for mass production of a novel laccase3 (Lac3) by recombinant Saccharomyces cerevisiae TYEGLAC3-1. The basic medium was composed of glucose, casamino acids, yeast nitrogen base without amino acids (YNB w/o AA), tryptophan, and adenine. A one-factor-at-a-time approach followed by the fractional factorial design identified galactose, glutamic acid, and ammonium sulfate, as significant carbon, nitrogen, and mineral sources, respectively. The steepest ascent method and response surface methodology (RSM) determined that the optimal medium was (g/L): galactose, 19.16; glutamic acid, 5.0; and YNB w/o AA, 10.46. In this medium, the Lac3 activity (277.04 mU/mL) was 13.5 times higher than that of the basic medium (20.50 mU/mL). The effect of temperature, pH, agitation (rpm), and aeration (vvm) was further examined in a batch fermenter. The best Lac3 activity was 1176.04 mU/mL at 25 °C, pH 3.5, 100 rpm, and 1 vvm in batch culture.

Directed Evolution of a Homodimeric Laccase from Cerrena unicolor BBP6 by Random Mutagenesis and In Vivo Assembly

Laccases have great potential for industrial applications due to their green catalytic properties and broad substrate specificities, and various studies have attempted to improve the catalytic performance of these enzymes. Here, to the best of our knowledge, we firstly report the directed evolution of a homodimeric laccase from Cerrena unicolor BBP6 fused with α-factor prepro-leader that was engineered through random mutagenesis followed by in vivo assembly in Saccharomyces cerevisiae. Three evolved fusion variants selected from ~3500 clones presented 31- to 37-fold increases in total laccase activity, with better thermostability and broader pH profiles. The evolved α-factor prepro-leader enhanced laccase expression levels by up to 2.4-fold. Protein model analysis of these variants reveals that the beneficial mutations have influences on protein pKa shift, subunit interaction, substrate entrance, and C-terminal function.