Refolding, characterization, and dye decolorization ability of a highly thermostable laccase from Geobacillus sp. JS12

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

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

Biodegradation of bisphenol A by a Pichia pastoris whole-cell biocatalyst with overexpression of laccase from Bacillus pumilus and investigation of its potential degradation pathways

Bisphenol A (BPA), an endocrine disrupter with estrogen activity, can infiltrate animal and human bodies through the food chain. Enzymatic degradation of BPA holds promise as an environmentally friendly approach while it is limited due to lower stability and recycling challenges. In this study, laccase from Bacillus pumilus TCCC 11568 was expressed in Pichia pastoris (fLAC). The optimal catalytic conditions for fLAC were at pH 6.0 and 80 °C, with a half-life T1/2 of 120 min at 70 °C. fLAC achieved a 46 % degradation rate of BPA, and possible degradation pathways were proposed based on identified products and reported intermediates of BPA degradation. To improve its stability and degradation capacity, a whole-cell biocatalyst (WCB) was developed by displaying LAC (dLAC) on the surface of P. pastoris GS115. The functionally displayed LAC demonstrated enhanced thermostability and pH stability along with an improved BPA degradation ability, achieving a 91 % degradation rate. Additionally, dLAC maintained a degradation rate of over 50 % after the fourth successive cycles. This work provides a powerful catalyst for degrading BPA, which might decontaminate endocrine disruptor-contaminated water through nine possible pathways.

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.

Exploring laccase: a sustainable enzymatic solution for the paper recycling domain

The global advocacy of resource conservation and waste management emphasizes the significance of sustainable practices, particularly in sectors such as paper manufacturing and recycling. Currently, conventional chemical methods are predominant for paper production, necessitating the use of substantial amount of toxic chemicals. This chemical-intensive approach compromises the recycled fiber quality, generates hazardous effluent causing serious ecological threats which triggers regulatory complexities for the mills. To address these challenges modern research suggests adopting sustainable eco-friendly practices such as employing enzymes. This review aims to explore the applicability of 'laccase' enzyme for paper recycling, investigating its properties and contribution to improved recycling practices. By delving into the potential application of laccase integration into the papermaking process, this article sheds light on the limitations inherent in traditional methods surmounted within both research and translational landscapes. Culture and process optimization studies, supporting the technological improvements and the future prospects have been documented.

Harnessing the power of bacterial laccases for xenobiotic degradation in water: A 10-year overview

Industrialization and population growth are leading to the production of significant amounts of sewage containing hazardous xenobiotic compounds. These compounds pose a threat to human and animal health, as well as the overall ecosystem. To combat this issue, chemical, physical, and biological techniques have been used to remove these contaminants from water bodies affected by human activity. Biotechnological methods have proven effective in utilizing microorganisms and enzymes, particularly laccases, to address this problem. Laccases possess versatile enzymatic characteristics and have shown promise in degrading different xenobiotic compounds found in municipal, industrial, and medical wastewater. Both free enzymes and crude enzyme extracts have demonstrated success in the biotransformation of these compounds. Despite these advancements, the widespread use of laccases for bioremediation and wastewater treatment faces challenges due to the complex composition, high salt concentration, and extreme pH often present in contaminated media. These factors negatively impact protein stability, recovery, and recycling processes, hindering their large-scale application. These issues can be addressed by focusing on large-scale production, resolving operation problems, and utilizing cutting-edge genetic and protein engineering techniques. Additionally, finding novel sources of laccases, understanding their biochemical properties, enhancing their catalytic activity and thermostability, and improving their production processes are crucial steps towards overcoming these limitations. By doing so, enzyme-based biological degradation processes can be improved, resulting in more efficient removal of xenobiotics from water systems. This review summarizes the latest research on bacterial laccases over the past decade. It covers the advancements in identifying their structures, characterizing their biochemical properties, exploring their modes of action, and discovering their potential applications in the biotransformation and bioremediation of xenobiotic pollutants commonly present in water sources.

Heterologous expression, purification, and characterization of thermo- and alkali-tolerant laccase-like multicopper oxidase from Bacillus mojavensis TH309 and determination of its antibiotic removal potential

Laccases or laccase-like multicopper oxidases have great potential in bioremediation to oxidase phenolic or non-phenolic substrates. However, their inability to maintain stability in harsh environmental conditions and against non-substrate compounds is one of the main reasons for their limited use. The gene (mco) encoding multicopper oxidase from Bacillus mojavensis TH309 were cloned into pET14b( +), expressed in Escherichia coli, and purified as histidine tagged enzyme (BmLMCO). The molecular weight of the enzyme was about 60 kDa. The enzyme exhibited laccase-like activity toward 2,6-dimethoxyphenol (2,6-DMP), syringaldazine (SGZ), and 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid) (ABTS). The highest enzyme activity was recorded at 80 °C and pH 8. BmLMCO showed a half-life of ~ 305, 99, 50, 46, 36, and 20 min at 40, 50, 60, 70, 80, and 90 °C, respectively. It retained more than 60% of its activity after pre-incubation in the range of pH 5-12 for 60 min. The enzyme activity significantly increased in the presence of 1 mM of Cu2+. Moreover, BmLMCO tolerated various chemicals and showed excellent compatibility with organic solvents. The Michaelis constant (Km) and the maximum velocity (Vmax) values of BmLMCO were 0.98 mM and 93.45 µmol/min, respectively, with 2,6-DMP as the substrate. BmLMCO reduced the antibacterial activity of cefprozil, gentamycin, and erythromycin by 72.3 ± 1.5%, 79.6 ± 6.4%, and 19.7 ± 4.1%, respectively. This is the first revealing shows the recombinant production of laccase-like multicopper oxidase from any B. mojavensis strains, its biochemical properties, and potential for use in bioremediation.

Recombinant expression and characterization of a new laccase, bioinformatically identified, from the Antarctic thermophilic bacterium Geobacillus sp. ID17

Geobacillus sp. ID17 is a gram-positive thermophilic bacterium isolated from Deception Island, Antarctica, which has shown to exhibit remarkable laccase activity in crude extract at high temperatures. A bioinformatic search using local databases led to the identification of three putative multicopper oxidase sequences in the genome of this microorganism. Sequence analysis revealed that one of those sequences contains the four-essential copper-binding sites present in other well characterized laccases. The gene encoding this sequence was cloned and overexpressed in Escherichia coli, partially purified and preliminary biochemically characterized. The resulting recombinant enzyme was recovered in active and soluble form, exhibiting optimum copper-dependent laccase activity at 55 °C, pH 6.5 with syringaldazine substrate, retaining over 60% of its activity after 1 h at 55 and 60 °C. In addition, this thermophilic enzyme is not affected by common inhibitors SDS, NaCl and L-cysteine. Furthermore, biodecolorization assays revealed that this laccase is capable of degrading 60% of malachite green, 54% of Congo red, and 52% of Remazol Brilliant Blue R, after 6 h at 55 °C with aid of ABTS as redox mediator. The observed properties of this enzyme and the relatively straightforward overexpression and partial purification of it could be of great interest for future biotechnology applications.

Evaluating the efficacy of wood decay fungi and synthetic fungal consortia for simultaneous decolorization of multiple textile dyes

Wastewater from the textile industry dyeing process containing high loads of synthetic dyes leads to pollution of water with these toxic and genotoxic dyes. Much effort has been put towards developing biological systems to resolve this issue. Mycoremediation is a well-known approach using fungi to remove, degrade, or remediate pollutants and can be applied to decolorize textile dyes in industrial effluent. Fungal strains from four genera of Polyporales, namely Coriolopsis sp. TBRC 2756, Fomitopsis pinicola TBRC-BCC 30881, Rigidoporus vinctus TBRC 6770, and Trametes pocas TBRC-BCC 18705, were studied for decolorization efficiency, and R. vinctus was found to exhibit the greatest activity in removing all seven tested reactive dyes and one acid dye with a decolorization efficiency of 80% or more within 7 days under limited oxygen. This fungus simultaneously degraded multiple dyes in synthetic wastewater as well as industrial effluent from the dyeing process. To enhance the decolorization rate, various fungal consortia were formulated for testing. However, these consortia only trivially improved efficiency compared with using R. vinctus TBRC 6770 alone. Evaluation of R. vinctus TBRC 6770 decolorization ability was further performed in a 15-L bioreactor to test its ability to eliminate multiple dyes from industrial effluent. The fungus took 45 days to adapt to growth in the bioreactor and subsequently reduced dye concentration to less than 10% of the initial concentration. The following six cycles required only 4-7 days to reduce dye concentrations to less than 25%, demonstrating that the system can run efficiently for multiple cycles without the need for extra medium or other carbon sources.

Heterogeneous biocatalytic system for effective decolorization of textile dye effluent

The current physicochemical methods for decolorizing toxic synthetic dyes are not sustainable to halt the environmental damage as they are expensive and often produce concentrated sludge, which may lead to secondary disposal problems. Biocatalysis (microbes and/or their enzymes) is a cost-effective, versatile, energy-saving and clean alternative. The most common enzymes involved in dye degradation are laccases, azoreductases and peroxidases. Toxic dyes could be converted into less harmful byproducts through the combined action of many enzymes or the utilization of whole cells. The action of whole cells to treat dye effluents is either by biosorption or degradation (aerobic or anaerobic). Using immobilized cells or enzymes will offer advantages such as superior stability, persistence against harsh environmental conditions, reusability and longer half-lives. This review envisages the recent strategies of immobilization and bioreactor considerations with the immobilized system as the effective treatment of textile dye effluents. Packed bed reactors are the most popular heterogeneous biocatalytic reactors for dye decolorization due to their efficiency and cost-effectiveness.

Preparation and characterization of a laccase-like enzyme from Thermomicrobium roseum

In this study, a laccase-like gene from Thermomicrobium roseum DSM 5159 (TrLac-like) (NCBI: WP_012642205.1) was recombinantly expressed in Bacillus subtilis WB600. The optimum temperature and pH for TrLac-like were 50 °C and 6.0, respectively. TrLac-like showed high tolerance to mixed systems of water and organic solvents, indicating its potential for large-scale application in various industries. It showed 36.81 % similarity with YlmD from Geobacillus stearothermophilus (PDB:6T1B) in sequence alignment; therefore, 6T1B was employed as the template for homology modeling. To improve catalytic efficiency, amino acid substitutions within 5 Å of the inosine ligand were simulated to reduce the binding energy and promote substrate affinity. Single and double substitutions (44 and 18, respectively) were prepared, and the catalytic efficiency of the mutant A248D was increased to approximately 110-fold that of the wild type, while the thermal stability was maintained. Bioinformatics analysis revealed that the significant improvement in catalytic efficiency could be attributed to the formation of new hydrogen bonds between the enzyme and substrate. With a further decrease in the binding energy, the catalytic efficiency of the multiple mutant H129N/A248D was approximately 14-fold higher than that of the wild type but lower than that of the single mutant A248D. This is possibly because k_cat also decreased with the decrease of K_m; consequently, the substrate could not be released in time owing to the enzyme with the combination mutation not being able to release the substrate at a high rate.

Inclusion Bodies: Status Quo and Perspectives

Multiple E. coli cultivations, producing recombinant proteins, lead to the formation of inclusion bodies (IBs). IBs historically were considered as nondesired by-products, due to their time- and cost-intensive purification. Nowadays, many obstacles in IB processing can be overcome. As a consequence, several industrial processes with E. coli favor IB formation over soluble production options due to the high space time yields obtained. Within this chapter, we discuss the state-of-the art biopharmaceutical IB process, review its challenges, highlight the recent developments and perspectives, and also propose alternative solutions, compared to the state-of-the art processing.

Characteristics and polyethylene biodegradation function of a novel cold-adapted bacterial laccase from Antarctic sea ice psychrophile Psychrobacter sp. NJ228

Biotreatment of polyethylene (PE) waste is an emerging topic in environmental remediation; in particular, the degrading enzymes requires further exploration. This study described a novel cold-adapted laccase (PsLAC) from an Antarctic psychrophile and characterized its PE-degradation ability. Homology modeling revealed that PsLAC possessed a typical bacterial laccase catalytic structure and unique cold adaptation structural characteristics such as few hydrogen bonds. Recombinant PsLAC (rPsLAC) retained 54.3% residual activity at 0 ℃ and presented increased K_m values at low temperatures and a relatively high k_cat value (42.65 s^-1). Collectively, these factors help resist cold stress. rPsLAC possessed substantial salt tolerance at 1.5 M NaCl, with 119.80% activity, and Cu²⁺ enhanced its activity to 127.10%. PE-degradation experiments indicated that 13.2% weight was lost, and the water contact angle was decreased to 74.6°. Polar functional groups such as carbonyl and carboxyl groups on PE surface were detected in Fourier transform infrared spectroscopy; X-ray diffraction exhibited that crystallinity reduced by 25%. Enormous damage to PE surface and interior was observed via scanning electron microscopy. Overall, PsLAC, with its unique cold-adapted catalytic structure and biochemical characteristics, could supplement the diversity of sources and properties of bacterial laccases and ensure PE-degradation with a novel cold-adapted enzyme resource.

Purification and biochemical characterization of a new thermostable laccase from Enterococcus faecium A2 by a three-phase partitioning method and investigation of its decolorization potential

Three-phase partitioning (TPP) is a simple, fast, cost-effective, and highly efficient process that can be used in the purification of laccases. In this study, microorganisms with laccase activity were isolated from water samples collected from the Agri-Diyadin hot spring. The isolate with the highest laccase activity was found to be the A2 strain. As a result of molecular (16S rRNA sequence) and conventional (morphological, biochemical, and physiological) analyses, it was determined that the A2 isolate was 99% similar to Enterococcus faecium (Genbank number: MH424896). The laccase was purified to 4.9-fold with 110% recovery using the TPP. The molecular mass of the enzyme was found by SDS-PAGE to be 50.11 kDa. Optimum pH 6.0 and optimum temperature for laccase were determined as 80 °C. The laccase exhibited pH stability over a wide range (pH 3.0-9.0) and a high thermostability, retaining over 90% of its activity after 1 h of incubation at 20-90 °C. The laccase exhibited high thermostability, with a heat inactivation half-life of approximately 24 h at 80 °C. The enzyme remained highly stable in the presence of surfactants and increased its activity in the presence of organic solvents, Cr²⁺, Cu²⁺, and Ag⁺ metal ions. The K_m, V_max, k_cat, and k_cat/K_m values of laccase for 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) substrate were 0.68 mM, 5.29 μmol mL^-1 min^-1, 110.2 s^-1, and 162.1 s^-1 mM^-1, respectively.

Identification and Characterization of a New Serratia proteamaculans Strain That Naturally Produces Significant Amount of Extracellular Laccase

Natural biodegradation processes hold promises for the conversion of agro-industrial lignocellulosic biomaterials into biofuels and fine chemicals through lignin-degrading enzymes. The high cost and low stability of these enzymes remain a significant challenge to economic lignocellulosic biomass conversion. Wood-degrading microorganisms are a great source for novel enzyme discoveries. In this study, the decomposed wood samples were screened, and a promising γ-proteobacterial strain that naturally secreted a significant amount of laccase enzyme was isolated and identified as Serratia proteamaculans AORB19 based on its phenotypic and genotypic characteristics. The laccase activities in culture medium of strain AORB19 were confirmed both qualitatively and quantitatively. Significant cultural parameters for laccase production under submerged conditions were identified following a one-factor-at-a-time (OFAT) methodology: temperature 30°C, pH 9, yeast extract (2 g/l), Li+, Cu2+, Ca2+, and Mn2+ (0.5 mM), and acetone (5%). Under the selected conditions, a 6-fold increase (73.3 U/L) in laccase production was achieved when compared with the initial culturing conditions (12.18 U/L). Furthermore, laccase production was enhanced under alkaline and mesophilic growth conditions in the presence of metal ions and organic solvents. The results of the study suggest the promising potential of the identified strain and its enzymes in the valorization of lignocellulosic wastes. Further optimization of culturing conditions to enhance the AORB19 strain laccase secretion, identification and characterization of the purified enzyme, and heterologous expression of the specific enzyme may lead to practical industrial and environmental applications.

Improving the decolorization activity of Bacillus pumilus W3 CotA-laccase to Congo Red by rational modification

Congo Red (CR) is a typical azo dye with highly toxic and carcinogenic properties. This study aimed to improve the decolorization activity of Bacillus pumilus W3 CotA-laccase for azo dye CR. This work analyzed the interaction between CotA-laccase and CR based on homology modeling and molecular docking. The three amino acids (Gly323, Thr377, Thr418) in the substrate-binding pocket were rationally modified through saturation mutation. Finally, the obtained multi-site mutants T377I/T418G and G323S/T377I/T418G decolorized 76.59% and 59.37% of CR within 24 h at pH 8.0 without a mediator, which were 3.15- and 2.44-fold higher than the wild-type CotA. The catalytic efficiency of the multi-site mutants T377I/T418G and G323S/T377I/T418G to CR were increased by 2.21- and 2.01-fold compared with the wild-type CotA, respectively. The mechanism of activity enhancement of mutants was proposed by structural analysis. This evidence suggests that the mutants T377I/T418G and G323S/T377I/T418G could be used as novel bioremediation tools.

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.

Recombinant expression of insoluble enzymes in Escherichia coli: a systematic review of experimental design and its manufacturing implications

Recombinant enzyme expression in Escherichia coli is one of the most popular methods to produce bulk concentrations of protein product. However, this method is often limited by the inadvertent formation of inclusion bodies. Our analysis systematically reviews literature from 2010 to 2021 and details the methods and strategies researchers have utilized for expression of difficult to express (DtE), industrially relevant recombinant enzymes in E. coli expression strains. Our review identifies an absence of a coherent strategy with disparate practices being used to promote solubility. We discuss the potential to approach recombinant expression systematically, with the aid of modern bioinformatics, modelling, and ‘omics’ based systems-level analysis techniques to provide a structured, holistic approach. Our analysis also identifies potential gaps in the methods used to report metadata in publications and the impact on the reproducibility and growth of the research in this field.

Extremophiles, a Nifty Tool to Face Environmental Pollution: From Exploitation of Metabolism to Genome Engineering

Extremophiles are microorganisms that populate habitats considered inhospitable from an anthropocentric point of view and are able to tolerate harsh conditions such as high temperatures, extreme pHs, high concentrations of salts, toxic organic substances, and/or heavy metals. These microorganisms have been broadly studied in the last 30 years and represent precious sources of biomolecules and bioprocesses for many biotechnological applications; in this context, scientific efforts have been focused on the employment of extremophilic microbes and their metabolic pathways to develop biomonitoring and bioremediation strategies to face environmental pollution, as well as to improve biorefineries for the conversion of biomasses into various chemical compounds. This review gives an overview on the peculiar metabolic features of certain extremophilic microorganisms, with a main focus on thermophiles, which make them attractive for biotechnological applications in the field of environmental remediation; moreover, it sheds light on updated genetic systems (also those based on the CRISPR-Cas tool), which expand the potentialities of these microorganisms to be genetically manipulated for various biotechnological purposes.

Current Development in Decolorization of Synthetic Dyes by Immobilized Laccases

The world today is in a quest for new means of environmental remediation as the methods currently used are not sufficient to halt the damage. Mostly, a global direction is headed toward a shift from traditional chemical-based methods to a more ecofriendly alternative. In this context, biocatalysis is seen as a cost-effective, energy saving, and clean alternative. It is meant to catalyze degradation of recalcitrant chemicals in an easy, rapid, green, and sustainable manner. One already established application of biocatalysis is the removal of dyes from natural water bodies using enzymes, notably oxidoreductases like laccases, due to their wide range of substrate specificity. In order to boost their catalytic activity, various methods of enhancements have been pursued including immobilization of the enzyme on different support materials. Aside from increased catalysis, immobilized laccases have the advantages of higher stability, better durability against harsh environment conditions, longer half-lives, resistance against protease enzymes, and the ability to be recovered for reuse. This review briefly outlines the current methods used for detoxification and decolorization of dye effluents stressing on the importance of laccases as a revolutionary biocatalytic solution to this environmental problem. This work highlights the significance of laccase immobilization and also points out some of the challenges and opportunities of this technology.