Cloning, expression and characterization of laccase from Bacillus licheniformis NS2324 in E. coli application in dye decolorization

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.

Efficient degradation and detoxification of structurally different dyes and mixed dyes by LAC-4 laccase purified from white-rot fungi Ganoderma lucidum

The purpose of this study is to evaluate the decolorization ability and detoxification effect of LAC-4 laccase on various types of single and mixed dyes, and lay a good foundation for better application of laccase in the efficient treatment of dye pollutants. The reaction system of the LAC-4 decolorizing single dyes (azo, anthraquinone, triphenylmethane, and indigo dyes, 17 dyes in total) were established. To explore the decolorization effect of the dye mixture by LAC-4, two dyes of the same type or different types were mixed at the same concentration (100 mg/L) in the reaction system containing 0.5 U laccase, and time-course decolorization were performed on the dye mixture. The combined dye mixtures consisted of azo + azo, azo + anthraquinone, azo + indigo, azo + triphenylmethane, indigo + triphenylmethane, and triphenylmethane + triphenylmethane. The results obtained in this study were as follows. Under optimal conditions of 30 °C and pH 5.0, LAC-4 (0.5 U) can efficiently decolorize four different types of dyes. The 24-hour decolorization efficiencies of LAC-4 for 800 mg/L Orange G and Acid Orange 7 (azo), Remazol Brilliant Blue R (anthraquinone), Bromophenol Blue and Methyl Green (triphenylmethane), and Indigo Carmine (indigo) were 75.94%, 93.30%, 96.56%, 99.94%, 96.37%, and 37.23%, respectively. LAC-4 could also efficiently decolorize mixed dyes with different structures. LAC-4 can achieve a decolorization efficiency of over 80% for various dye mixtures such as Orange G + Indigo Carmine (100 mg/L+100 mg/L), Reactive Orange 16 + Methyl Green (100 mg/L+100 mg/L), and Remazol Brilliant Blue R + Methyl Green (100 mg/L+100 mg/L). During the decolorization process of the mixed dyes by laccase, four different interaction relationships were observed between the dyes. Decolorization efficiencies and rates of the dyes that were difficult to be degraded by laccase could be greatly improved when mixed with other dyes. Degradable dyes could greatly enhance the ability of LAC-4 to decolorize extremely difficult-to-degrade dyes. It was also found that the decolorization efficiencies of the two dyes significantly increased after mixing. The possible mechanisms underlying the different interaction relationships were further discussed. Free, but not immobilized, LAC-4 showed a strong continuous batch decolorization ability for single dyes, two-dye mixtures, and four-dye mixtures with different structures. LAC-4 exhibited high stability, sustainable degradability, and good reusability in the continuous batch decolorization. The LAC-4-catalyzed decolorization markedly reduced or fully abolished the toxic effects of single dyes (azo, anthraquinone, and indigo dye) and mix dyes (nine dye mixtures containing four structural types of dyes) on plants. Our findings indicated that LAC-4 laccase had significant potential for use in bioremediation due to its efficient degradation and detoxification of single and mixed dyes with different structural types.

Cloning, expression and application of a novel laccase derived from water buffalo ruminal lignin-degrading bacteria

Water buffalo is the only mammal found to degrade lignin so far, and laccase plays an indispensable role in the degradation of lignin. In this study, multiple laccase genes were amplified based on the water buffalo rumen derived lignin-degrading bacteria Bacillus cereus and Ochrobactrum pseudintermedium. Subsequently, the corresponding recombinant plasmids were transformed into E. coli expression system BL21 (DE3) for induced expression by Isopropyl-β-D-thiogalactopyranoside (IPTG). After preliminary screening, protein purification and enzyme activity assays, Lac3833 with soluble expression and high enzyme activity was selected to test its characteristics, especially the ability of lignin degradation. The results showed that the optimum reaction temperature of Lac3833 was 40 °C for different substrates. The relative activity of Lac3833 reached the highest at pH 4.5 and pH 5.5 when the substrates were ABTS or 2,6-DMP and guaiacol, respectively. Additionally, Lac3833 could maintain high enzyme activity in different temperatures, pH and solutions containing Na+, K+, Mg2+, Ca2+ and Mn2+. Importantly, compared to negative treatment, recombinant laccase Lac3833 treatment showed that it had a significant function in degrading lignin. In conclusion, this is a pioneering study to produce recombinant laccase with lignin-degrading ability by bacteria from water buffalo rumen, which will provide new insights for the exploitation of more lignin-degrading enzymes.

Electricity generation and oxidoreductase potential during dye discoloration by laccase-producing Ganoderma gibbosum in fungal fuel cell

Color chemicals contaminate pure water constantly discharged from different points and non-point sources. Physical and chemical techniques have certain limitations and complexities for bioenergy production, which motivated the search for a novel sustainable production approaches during dye wastewater treatment. The emerging environmental problem of dye decolorization has attracted scientist's attention to a new, cheap, and economical way to treat dye wastewater and power production via fungal fuel cells. Ganoderma gibbosum was fitted in the cathodic region with laccase secretion in the fuel cell. At the same time, dye water was placed in the anodic region to move electrons and produce power. This study treated wastewater using the oxidoreductase enzymes released extracellularly from Ganoderma gibbosum for dye Remazol Brilliant Blue R (RBBR) degradation via fungal-based fuel cell. The maximum power density of 14.18 mW/m2 and the maximum current density of 35 mA/m2 were shown by the concentration of 5 ppm during maximum laccase activity and decolorization of RBBR. The laccase catalysts have gained considerable attention because of eco-friendly and alternative easy handling approaches to chemical methods. Fungal Fuel Cells (FFCs) are efficiently used in dye treatment and electricity production. This article also highlighted the construction of fungal catalytic cells and the enzymatic performance of fungal species in energy production during dye water treatment.

Expression and Characterization of Laccase Lac1 from Coriolopsis trogii Strain Mafic-2001 in Pichia pastoris and Its Degradation of Lignin

The laccase gene (Lac1) was cloned from Coriolopsis trogii strain Mafic-2001. Full-length sequence of Lac1 containing 11 exons and 10 introns is composed of 2140 nucleotides (nts). mRNA of Lac1 encoded for a protein of 517 aa. Nucleotide sequence of the laccase was optimized and expressed in Pichia pastoris X-33. SDS-PAGE analysis showed that the molecular weight of the purified recombinant laccase rLac1 was about 70 kDa. The optimum temperature and pH of rLac1 were 40 ℃ and 3.0, respectively. rLac1 showed high residual activity (90%) in the solutions after 1 h incubation at the pH ranging from 2.5 to 8.0. rLac1 maintained over 60% of laccase activity at the temperatures ranging from 20 to 60 °C, and kept higher than 50% of its activity at 40 °C for 2 h. The activity of rLac1 was promoted by Cu2+ and inhibited by Fe2+. Under optimal conditions, lignin degradation rates of rLac1 on the substrates of rice straw, corn stover, and palm kernel cake were 50.24%, 55.49%, and 24.43% (the lignin contents of substrates untreated with rLac1 were 100%), respectively. Treated with rLac1, the structures of agricultural residues (rice straw, corn stover, and palm kernel cake) were obviously loosened which was reflected by the analysis of scanning electron microscopy and Fourier transform infrared spectroscopy. Based on the specific activity of rLac1 on the degradation of lignin, rLac1 from Coriolopsis trogii strain Mafic-2001 has the potential for in-depth utilization of agricultural residues.

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.

Computer-aided discovery of a novel thermophilic laccase for low-density polyethylene degradation

Polyethylene (PE) and industrial dyes are recalcitrant pollutants calling for the development of sustainable solutions for their degradation. Laccases have been explored for removal of contaminants and pollutants, including dye decolorization and plastic degradation. Here, a novel thermophilic laccase from PE-degrading Lysinibaccillus fusiformis (LfLAC3) was identified through a computer-aided and activity-based screening. Biochemical studies of LfLAC3 indicated its high robustness and catalytic promiscuity. Dye decolorization experiments showed that LfLAC3 was able to degrade all the tested dyes with decolorization percentage from 39% to 70% without the use of a mediator. LfLAC3 was also demonstrated to degrade low-density polyethylene (LDPE) films after eight weeks of incubation with either crude cell lysate or purified enzyme. The formation of a variety of functional groups was detected using Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). Damage on the surfaces of PE films was observed via scanning electron microscopy (SEM). The potential catalytic mechanism of LfLAC3 was disclosed by structure and substrate-binding modes analysis. These findings demonstrated that LfLAC3 is a promiscuous enzyme that has promising potential for dye decolorization and PE degradation.

Isolation and Characterization of a Novel Laccase-Producing Bacteria Bhargavaea beijingensis from Paper and Pulp Effluent-Treated Soil Using In Silico Approaches

Laccases (EC 1.10.3.2) are considered one of the most prominent multicopper enzymes that exhibit the inherent properties of oxidizing a range of phenolic substrates. Mostly, reported laccases have been isolated from the plants and fungi species, whereas bacterial laccases are yet to be explored. Bacterial laccases have numerous distinctive properties over fungal laccases, including stability at high temperatures and high pH. This study includes the isolation of bacteria through the soil sample collected from the paper and pulp industry; the highest laccase-producing bacteria was identified as Bhargavaea bejingensis, using 16S rRNA gene sequencing. The extracellular and intracellular activities after 24 h incubation were 1.41 U/mL and 4.95 U/mL, respectively. The laccase-encoding gene of the bacteria was sequenced; moreover, the in vitro translated protein was bioinformatically characterized and asserted that the laccase produced by the bacteria Bhargavaea bejingensis was structurally and sequentially homologous to the CotA protein of Bacillus subtilis. The enzyme laccase produced from B. bejingensis was classified as three-domain laccase with several copper-binding residues, where a few crucial copper-binding residues of the laccase enzyme were also predicted.

Degradation of Aflatoxin B1 by recombinant laccase extracellular produced from Escherichia coli

Bioenzymatic degradation of aflatoxin B1 (AFB1) is a safe, efficient and environmentally friendly detoxification technology. In this work, AFB1 was successfully degraded by recombinant laccase (fmb-rL103) in the absence of a mediator. The laccase gene was cloned from Bacillus vallismortis fmb-103, and was expressed in heterologous host Escherichia coli after codon optimization. The extracellular production of fmb-rL103 could be induced by adding methanol (6 %, v/v), and the maximum yield was 1545.6 U/L. In the 10 L bioreactor, the extracellular yield increased to 50,950.6 U/L after 20 h of induction, accounting for three quarters of the total yield. The mechanism of methanol-induced extracellular secretion was further studied by measuring acetate content, lac103 gene expression and cell membrane permeability. Furthermore, we explored the biochemical properties of fmb-rL103 and its degradation conditions on AFB1. The degradation efficiency increased constantly with increase in incubation pH and temperature, and exceeded 60 % at pH 7.0 and 37 °C. This work provides new insight into developing the large-scale production of laccase and its application to degrade AFB1.