Isolation and biochemical characterization of laccase and tyrosinase activities in a novel melanogenic soil bacterium

Exploring the Agricultural Applications of Microbial Melanin

Microbial melanins are a group of pigments with protective effects against harsh conditions, showing fascinating photoprotective activities, mainly due to their capability to absorb UV radiation. In bacteria, they are produced by the oxidation of L-tyrosine, generating eumelanin and pheomelanin. Meanwhile, allomelanin is produced by fungi through the decarboxylative condensation of malonyl-CoA. Moreover, melanins possess antioxidant and antimicrobial activities, revealing significant properties that can be used in different industries, such as cosmetic, pharmaceutical, and agronomical. In agriculture, melanins have potential applications, including the development of new biological products based on this pigment for the biocontrol of phytopathogenic fungi and bacteria to reduce the excessive and toxic levels of agrochemicals used in fields. Furthermore, there are possibilities to develop and improve new bio-based pesticides that control pest insects through the use of melanin-producing and toxin-producing Bacillus thuringiensis or through the application of melanin to insecticidal proteins to generate a new product with improved resistance to UV radiation that can then be applied to the plants. Melanins and melanin-producing bacteria have potential applications in agriculture due to their ability to improve plant growth. Finally, the bioremediation of water and soils is possible through the application of melanins to polluted soils and water, removing synthetic dyes and toxic metals.

Fungi as a source of eumelanin: current understanding and prospects

Melanins represent a diverse collection of pigments with a variety of structures and functions. One class of melanin, eumelanin, is recognizable to most as the source of the dark black color found in cephalopod ink. Sepia officinalis is the most well-known and sought-after source of non-synthetic eumelanin, but its harvest is limited by the availability of cuttlefish, and its extraction from an animal source brings rise to ethical concerns. In recent years, these limitations have become more pressing as more applications for eumelanin are developed-particularly in medicine and electronics. This surge in interest in the applications of eumelanin has also fueled a rise in the interest of alternative, bio-catalyzed production methods. Many culinarily-utilized fungi are ideal candidates in this production scheme, as examples exist which have been shown to produce eumelanin, their growth at large scales is well understood, and they can be cultivated on recaptured waste streams. However, much of the current research on the fungal production of eumelanin focuses on pathogenic fungi and eumelanin's role in virulence. In this paper, we will review the potential for culinary fungi to produce eumelanin and provide suggestions for new research areas that would be most impactful in the search for improved fungal eumelanin producers.

Thermodynamics and Kinetics of Electron Transfer of Electrode-Immobilized Small Laccase from Streptomyces coelicolor

The thermodynamic and kinetic properties for heterogeneous electron transfer (ET) were measured for the electrode-immobilized small laccase (SLAC) from Streptomyces coelicolor subjected to different electrostatic and covalent protein-electrode linkages, using cyclic voltammetry. Once immobilized electrostatically onto a gold electrode using mixed carboxyl- and hydroxy-terminated alkane-thiolate SAMs or covalently exploiting the same SAM subjected to N-hydroxysuccinimide+1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide (NHS-EDC) chemistry, the SLAC-electrode electron flow occurs through the T1 center. The E°' values (from +0.2 to +0.1 V vs. SHE at pH 7.0) are lower by more than 0.2 V compared to the protein either in solution or immobilized with different anchoring strategies using uncharged SAMs. For the present electrostatic and covalent binding, this effect can, respectively, be ascribed to the negative charge of the SAM surfaces and to deletion of the positive charge of Lys/Arg residues due to amide bond formation which both selectively stabilize the more positively charged oxidized SLAC. Observation of enthalpy/entropy compensation within the series indicates that the immobilized proteins experience different reduction-induced solvent reorganization effects. The E°' values for the covalently attached SLAC are sensitive to three acid base equilibria, with apparent pK_a values of pK_a1ox = 5.1, pK_a1red = 7.5, pK_a2ox = 8.4, pK_a2red = 10.9, pK_a2ox = 8.9, pK_a2red = 11.3 possibly involving one residue close to the T1 center and two residues (Lys and/or Arg) along with moderate protein unfolding, respectively. Therefore, the E°' value of immobilized SLAC turns out to be particularly sensitive to the anchoring mode and medium conditions.

Elimination and detoxification of phenanthrene assisted by a laccase from halophile Alkalibacillus almallahensis

Phenanthrene (Phe), a tricyclic Polycyclic Aromatic Hydrocarbon (PAH), is found in high concentrations as a pollutant in various environments. In this study, the removal or (oxidizing) ability of Phe by a laccase from Alkalibacillus almallahensis was investigated. The laccase (12 U mL-1) was able to remove 63% of Phe (50 mg L-1) under optimal conditions of 40 °C, pH 8, 1.5 M NaCl and in the presence of 1 mM HBT as a laccase mediator after a 72 h incubation period. The results for the effect of different solvents, ionic and non-ionic surfactants on the activity of the halophilic laccase towards Phe showed that the addition of these compounds increase removal efficiency and complete enzymatic removal of Phe will achieve in a solution of 5% (v/v) acetone and 1.5% tween 80. The kinetic parameters K m and V max of laccase-catalyzed removal of the substrate were determined as 0.544 mM and 0.882 µmol h-1 mg-1, respectively. A microtoxicity study with respect to the inhibition of algal growth showed a decrease in toxicity of the laccase-treated Phe solution.

Laccase producing bacteria influenced the high decolorization of textile azo dyes with advanced study

Recent year, bacterial laccases are increasing interest in the field of industry and environmental applications especially decolorization of azo dyes. In industry, the dyes are present in stable nature including chemicals and lights. Due to these defects, the novel approaches are needed to removal of dyes before discharging into the environment. Among the various technologies, biological treatment methods and their strategies are very important, because of the decolorization and detoxification. Consecutively, biological mediated dyes removal are emerged with high potential especially microbes. Microbial laccases creates up new opportunities for their commercial applications. In this study, laccases were produced from Bacillus cereus (B. Cereus) and Pseudomonas parafulva (P. parafulva) by sub merged fermentation. For immobilization, the produced laccases were subjected to purify using 80% saturated ammonium sulphate and followed by dialysis. Then, crude laccases were immobilized through copper-alginate entrapment method. The maximum immobilized enzyme activity of the immobilized laccases were shown pH 8 at 50 °C and pH 7 at 40 °C for B. Cereus and P. parafulva respectively. In contrast, the normal enzyme activity was pH 10 at 40 °C and pH 8 at 40 °C were indicated for Bacillus cereus and P. parafulva respectively. Next, the free and immobilized laccases were performed the decolorization of three azo dyes T-blue, yellow GR and orange 3R, and exhibited that the 91.69 and 89.21% of Orange 3R were completely decolorized by both the B. Cereus and P. parafulva laccases when compared with free laccases enzymes. The confirmation of decolorization was monitored by UV-vis spectroscopy and FTIR spectroscopy, which clearly confirm the changes of peaks when compared with normal laccases. Finally, we have concluded that the B. Cereus and P. parafulva laccases are very important in azo dye decolorization and these used in future biological treatment of dyeing effluents.

Tyrosinase and laccase-producing Bacillus aryabhattai TFG5 and its role in the polymerization of phenols

BACKGROUND

Tyrosinases and laccases are oxidoreductase enzymes that are used widely in the food, feed, textile, and biofuel industries. The rapidly growing industrial demand for bacterial oxido-reductases has encouraged research on this enzyme worldwide. These enzymes also play a key role in the formation of humic substances (HS) that are involved in controlling the biogeochemical carbon cycle, providing nutrients and bio-stimulants for plant growth, and interacting with inorganic and organic pollutants besides increasing carbon sequestration and mitigating greenhouse gas emission in the environment. The present study aimed to screen and characterize extracellular tyrosinase and laccase-producing soil bacteria that could be utilized in the polymerization of phenols.

RESULTS

Twenty isolates from different soil samples collected from forest ecosystems were characterized through ARDRA using restriction digestion with AluI, HpaII, and HaeIII restriction enzymes. The results of Hierarchical Cluster Analysis (HCA) revealed a 60 % similarity coefficient among 13 out of 20 isolates, of which, the isolate TFG5 exhibited only 10 % similarity when compared to all the other isolates. The isolate TFG5 exhibited both tyrosinase (1.34 U.mL- 1) and laccase (2.01 U.mL- 1) activity and was identified as Bacillus aryabhattai. The increased polymerization activity was observed when B. aryabhattai TFG5 was treated with phenols. The monomers such as catechol, p-Hydroxy benzoic acid, ferulic acid, and salicylic acid were polymerized efficiently, as evidenced by their FT-IR spectra depicting increased functional groups compared to the standard mushroom tyrosinase.

CONCLUSIONS

The polymerization ability of B. aryabhattai TFG5 could be applied to phenol-rich wastewater treatment for efficient precipitation of phenols. Furthermore, tyrosinases can be used for enhancing the synthesis of HS in soil.

Microbial melanin: Recent advances in biosynthesis, extraction, characterization, and applications

Melanin is a common name for a group of biopolymers with the dominance of potential applications in medical sciences, cosmeceutical, bioremediation, and bioelectronic applications. The broad distribution of these pigments suggests their role to combat abiotic and biotic stresses in diverse life forms. Biosynthesis of melanin in fungi and bacteria occurs by oxidative polymerization of phenolic compounds predominantly by two pathways, 1,8-dihydroxynaphthalene [DHN] or 3,4-dihydroxyphenylalanine [DOPA], resulting in different kinds of melanin, i.e., eumelanin, pheomelanin, allomelanin, pyomelanin, and neuromelanin. The enzymes responsible for melanin synthesis belong mainly to tyrosinase, laccase, and polyketide synthase families. Studies have shown that manipulating culture parameters, combined with recombinant technology, can increase melanin yield for large-scale production. Despite significant efforts, its low solubility has limited the development of extraction procedures, and heterogeneous structural complexity has impaired structural elucidation, restricting effective exploitation of their biotechnological potential. Innumerable studies have been performed on melanin pigments from different taxa of life in order to advance the knowledge about melanin pigments for their efficient utilization in diverse applications. These studies prompted an urgent need for a comprehensive review on melanin pigments isolated from microorganisms, so that such review encompassing biosynthesis, bioproduction, characterization, and potential applications would help researchers from diverse background to understand the importance of microbial melanins and to utilize the information from the review for planning studies on melanin. With this aim in mind, the present report compares conventional and modern ideas for environment-friendly extraction procedures for melanin. Furthermore, the characteristic parameters to differentiate between eumelanin and pheomelanin are also mentioned, followed by their biotechnological applications forming the basis of industrial utilization. There lies a massive scope of work to circumvent the bottlenecks in their isolation and structural elucidation methodologies.

Enhancing the decolorization activity of Bacillus pumilus W3 CotA-laccase to Reactive Black 5 by site-saturation mutagenesis

Reactive Black 5 (RB5) is a typical refractory azo dye. Widespread utilization of RB5 has caused a variety of environmental and health problems. The enzymatic degradation of RB5 can be a promising solution due to its superiority as an eco-friendly and cost-competitive process. Bacterial CotA-laccase shows great application prospect to eliminate hazardous dyes from wastewater. However, efficient decolorization of RB5 CotA-laccase generally requires the participation of costly, toxic mediators. In the present study, we modified the amino acids Thr415 and Thr418 near the type 1 copper site and the amino acid Gln442 at the entrance of the substrate-binding pocket of Bacillus pumilus W3 CotA-laccase to boost its RB5 decolorization activity based on molecular docking analysis and site-saturation mutagenesis. Through the strategies, two double site mutants T415D/Q442A and T418K/Q442A obtained demonstrated 43.94 and 52.64% RB5 decolorization rates in the absence of a mediator at pH 10.0, respectively, which were about 3.70- and 4.43-fold higher compared with the wild-type CotA-laccase. Unexpectedly, the catalytic efficiency of the T418K/Q442A to ABTS was enhanced by 5.33-fold compared with the wild-type CotA-laccase. The mechanisms of conferring enhanced activity to the mutants were proposed by structural analysis. In summary, the mutants T415D/Q442A and T418K/Q442A have good application potentials for the biodegradation of RB5. KEY POINTS: • Three amino acids of CotA-laccase were manipulated by site-saturation mutagenesis. • Decolorization rate of two mutants to RB5 was enhanced 3.70- and 4.43-fold, respectively. • The mechanisms of awarding enhanced activity to the mutants were supposed.

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.

High Synteny and Sequence Identity between Genomes of Nitrosococcus oceani Strains Isolated from Different Oceanic Gyres Reveals Genome Economization and Autochthonous Clonal Evolution

The ammonia-oxidizing obligate aerobic chemolithoautotrophic gammaproteobacterium, Nitrosococcus oceani, is omnipresent in the world's oceans and as such important to the global nitrogen cycle. We generated and compared high quality draft genome sequences of N. oceani strains isolated from the Northeast (AFC27) and Southeast (AFC132) Pacific Ocean and the coastal waters near Barbados at the interface between the Caribbean Sea and the North Atlantic Ocean (C-27) with the recently published Draft Genome Sequence of N. oceani Strain NS58 (West Pacific Ocean) and the complete genome sequence of N. oceani C-107, the type strain (ATCC 19707) isolated from the open North Atlantic, with the goal to identify indicators for the evolutionary origin of the species. The genomes of strains C-107, NS58, C-27, and AFC27 were highly conserved in content and synteny, and these four genomes contained one nearly sequence-identical plasmid. The genome of strain AFC132 revealed the presence of genetic inventory unknown from other marine ammonia-oxidizing bacteria such as genes encoding NiFe-hydrogenase and a non-ribosomal peptide synthetase (NRPS)-like siderophore biosynthesis module. Comparative genome analysis in context with the literature suggests that AFC132 represents a metabolically more diverse ancestral lineage to the other strains with C-107 and NS58 potentially being the youngest. The results suggest that the N. oceani species evolved by genome economization characterized by the loss of genes encoding catabolic diversity while acquiring a higher redundancy in inventory dedicated to nitrogen catabolism, both of which could have been facilitated by their rich complements of CRISPR/Cas and Restriction Modification systems.

Melanin biosynthesis in bacteria, regulation and production perspectives

The production of black pigments in bacteria was discovered more than a century ago and related to tyrosine metabolism. However, their diverse biological roles and the control of melanin synthesis in different bacteria have only recently been investigated. The broad distribution of these pigments suggests that they have an important role in a variety of organisms. Melanins protect microorganisms from many environmental stress conditions, ranging from ultraviolet radiation and toxic heavy metals to oxidative stress. Melanins can also affect bacterial interactions with other organisms and are important in pathogenesis and survival in many environments. Bacteria produce several types of melanin through dedicated pathways or as a result of enzymatic imbalances in altered metabolic routes. The control of the melanin synthesis in bacteria involves metabolic and transcriptional regulation, but many aspects remain still largely unknown. The diverse properties of melanins have spurred a large number of applications, and recent efforts have been done to produce the pigment at biotechnologically relevant scales.

Enhancement in catalytic activity of CotA-laccase from Bacillus pumilus W3 via site-directed mutagenesis

CotA-laccases are potential enzymes that are widely used in decolorization of dyes and degradation of toxic substances. In this study, a novel CotA-laccase gene from Bacillus pumilus W3 was applied for rational design. After a series of site-directed genetic mutations, the mutant S208G/F227A showed a 5.1-fold higher catalytic efficiency (k_cat/K_m) than the wild-type CotA-laccase did. The optimal pH of S208G/F227A was 3.5 with ABTS as substrate. The residual activity of mutant S208G/F227A was more than 80% after incubated for 10 h at pH 7-11. Mutant S208G/F227A showed optimal temperature at 80°C with ABTS as substrate. The thermal stability of mutant laccase S208G/F227A was lower than that of wild-type CotA-laccase. This study showed that Gly208 and Ala227 play key roles in catalytic efficiency and it is possible to improve catalytic efficiency of CotA-laccase through site-directed mutagenesis.

Cohnella sp. A01 laccase: thermostable, detergent resistant, anti-environmental and industrial pollutants enzyme

Laccase (EC 1.10.3.2; benzenediol; oxygen oxidoreductases) is a multi-copper oxidase that catalyzes the oxidation of phenols, polyphenols, aromatic amines, and different non-phenolic substrates with concomitant reduction of O₂ to H₂O. Enzymatic oxidation techniques have the potential of implementation in different areas of industrial fields. In this study, the Cohnella sp. A01 laccase gene was cloned into pET-26 (b+) vector and was transformed to E. coli BL21. Then it was purified using His tag affinity (Ni sepharose resin) chromatography. The estimated molecular weight was approximately 60 kDa using SDS-PAGE. The highest enzyme activity and best pH for 2,6-dimethoxyphenol (DMP) oxidation were recorded as 8 at 90 °C respectively. The calculated half-life and kinetic values including K_m, V_max, turn over number (k_cat), and catalytic efficiency (k_cat/K_m) of the enzyme were 106 min at 90 °C and 686 μM, 10.69 U/ml, 20.3 S⁻, and 0.029 s⁻¹ μM⁻¹, respectively. The DMP was available as the substrate in all the calculations. Enzyme activity enhanced in the presence of Cu²⁺, NaCl, SDS, n-hexane, Triton X-100, tween 20, and tween 80, significantly. The binding residues were predicted and mapped upon the modeled tertiary structure of identified laccase. The remaining activity and structural properties of Cohnella sp. A01 laccase in extreme conditions such as high temperatures and presence of metals, detergents, and organic solvents suggest the potential of this enzyme in biotechnological and industrial applications. This process has been patented in Iranian Intellectual Property Centre under License No: 91325.

Aptitude of Oxidative Enzymes for Treatment of Wastewater Pollutants: A Laccase Perspective

Natural water sources are very often contaminated by municipal wastewater discharges which contain either of xenobiotic pollutants and their sometimes more toxic degradation products, or both, which frustrates the universal millenium development goal of provision of the relatively scarce pristine freshwater to water-scarce and -stressed communities, in order to augment their socioeconomic well-being. Seeing that both regulatory measures, as regards the discharge limits of wastewater, and the query for efficient treatment methods remain unanswered, partially, the prospects of enzymatic treatment of wastewater is advisable. Therefore, a reconsideration was assigned to the possible capacity of oxidative enzymes and the respective challenges encountered during their applications in wastewater treatment, and ultimately, the prospects of laccase, a polyphenol oxidase that oxidizes aromatic and inorganic substrates with electron-donating groups in treatment aromatic contaminants of wastewater, in real wastewater situations, since it is assumed to be a vehicle for a greener community. Furthermore, the importance of laccase-driven catalysis toward maintaining mass-energy balance, hence minimizing environmental waste, was comprehensibly elucidated, as well the strategic positioning of laccase in a model wastewater treatment facility for effective treatment of wastewater contaminants.

Lyoprotection and stabilization of laccase extract from Coriolus hirsutus, using selected additives

The development of stable lyophilized laccase, obtained from Coriolus hirsutus, using a wide range of temperature treatments and storage conditions, was investigated. Using selected lyoprotectants, including, dextran 6 kDa, sucrose and a mixture of sodium benzoate, potassium sorbate and sorbitol (BKSS) (1.5:1.0:98.5; w/w/w) resulted by 2.4, 1.4 and 1.8-fold increase in laccase activity after lyophilization as compared to the fresh enzyme, respectively, whereas the addition of mannitol preserved 98.2% of its activity. Using 2.5% (w/v) dextran (15-25 kDa) or mannitol appeared to be the most appropriate lyoprotectants for the laccase activity. The laccase stability of the lyophilized enzymatic extract was greatly enhanced with the presence of mannitol, with 96.2, 38.9 and 24.7% of residual activity after 4 weeks of storage at - 80, 4 and 25 °C, respectively. The inactivation constant (k_inactivation) value and the amount required to decrease 50% of the laccase activity (C_1/2) showed that Carbowax^® polyethylene glycol (PEG)-8000 was the most appropriate additive for laccase activity, followed by glycerol and CuSO₄. When the enzymatic extract was incubated at 50 °C in the presence of either CuSO₄, PEG-8000 or glycerol, the time required to decrease 50% of the laccase initial activity (t₅₀), were 52.9, 54.6, 50.2 h, respectively, as compared to that of the control trial of 38.9 h.

Isolation and characterization of a novel tyrosinase produced by Sahara soil actinobacteria and immobilization on nylon nanofiber membranes

In the present study different actinomycete strains were collected and isolated from Algerian Sahara soil with the aim to select novel enzymes with promising features for biotechnological applications. The Ms1 strain was selected, amongst the others, for its capability to produce melanin in different solid media. Ms1 chromosomal DNA was sequenced and the strain assigned to Streptomyces cyaneofuscatus sp. A tyrosinase (MW∼30kD) encoding sequence was identified and the corresponding enzyme was isolated and biochemically characterized. The tyrosinase showed the highest activity and stability at neutral and alkaline pH and it was able to oxidize l-DOPA at T=55°C and pH 7. The enzyme showed variable stability in presence of various water-miscible organic solvents, while it was inactivated by reducing agents. The tyrosinase activity was unaffected by NaCl and enhanced by different cations. Furthermore, the enzyme showed a higher specificity for diphenols than monophenols showing a higher diphenolase than monophenolase activity. Finally, tyrosinase was stabilized by immobilization on nylon nanofiber membranes with a payload of 82% when 1% glutaraldeyde was used. Taken all together, these results show that the enzyme displays interesting properties for biotechnological purposes.

Bacterial laccase: recent update on production, properties and industrial applications

Laccases (benzenediol: oxygen oxidoreductase, EC 1.10.3.2) are multi-copper enzymes which catalyze the oxidation of a wide range of phenolic and non-phenolic aromatic compounds in the presence or absence of a mediator. Till date, laccases have mostly been isolated from fungi and plants, whereas laccase from bacteria has not been well studied. Bacterial laccases have several unique properties that are not characteristics of fungal laccases such as stability at high temperature and high pH. Bacteria produce these enzymes either extracellularly or intracellularly and their activity is in a wide range of temperature and pH. It has application in pulp biobleaching, bioremediation, textile dye decolorization, pollutant degradation, biosensors, etc. Hence, comprehensive information including sources, production conditions, characterization, cloning and biotechnological applications is needed for the effective understanding and application of these enzymes at the industrial level. The present review provides exhaustive information of bacterial laccases reported till date.

Impact of phosphate and other medium components on physiological regulation of bacterial laccase production

Laccases are multicopper oxidases known to catalyze the transformation of a wide range of phenolic and non-phenolic substrates using oxygen as electron acceptor and forming water as the only by product. Their potential relevance in several industries requires the constant search for novel laccases. Positive outcome of the isolation of laccase producing bacteria depends on the nature and concentration of media constituents. Several attempts to isolate laccase producing bacteria failed when the phosphate-containing M9 minimal medium was used. Shift to phosphate-less M162 medium led to successful isolations. Seven bacterial isolates belonging to genera Bacillus, Lysinibacillus, Bhargavaea and Rheinheimera were used to study the effect of medium constituents on laccase production. Inorganic phosphate (≥50 mM) was found to regulate laccase synthesis negatively though no inhibitory effect of phosphate (10-500 mM) was seen on laccase activity. All isolates ceased laccase synthesis when grown in the presence of tryptone (0.2-1%), with R. tangshanensis as an exception, or yeast extract (1.5-2%) as the only C/N source in M162 medium. Supplementation upto 0.1% of glucose in basal M162 medium increased laccase production in five isolates but decreased at higher concentrations. The influence of medium components on laccase synthesis was further affirmed by zymographic studies. These observations offer possibilities of isolating promising laccase producers from diverse environmental sources. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 33:541-548, 2017.

Production of Extracellular Laccase from Bacillus subtilis MTCC 2414 Using Agroresidues as a Potential Substrate

Laccases are the model enzymes for multicopper oxidases and participate in several applications such as bioremediation, biopulping, textile, and food industries. Laccase producing bacterium, Bacillus subtilis MTCC 2414, was subjected to optimization by conventional techniques and was partially purified using ammonium salt precipitation method. The agroresidue substrates used for higher yield of laccase were rice bran and wheat bran. Maximum production was achieved at temperature 30°C (270 ± 2.78 U/mL), pH 7.0 (345 ± 3.14 U/mL), and 96 h (267 ± 2.64 U/mL) of incubation. The carbon and nitrogen sources resulted in high enzyme yield at 3% sucrose (275 ± 3.11 U/mL) and 3% peptone (352.2 ± 4.32 U/mL) for rice bran and 3% sucrose (247.4 ± 3.51 U/mL) and 3% peptone (328 ± 3.33 U/mL) for wheat bran, respectively. The molecular weights of partially purified laccase were 52 kDa for rice bran and 55 kDa for wheat bran. The laccase exhibited optimal activity at 70°C (260.3 ± 6.15 U/mL), pH 9.0 (266 ± 4.02 U/mL), and metal ion CuSO4 (141.4 ± 6.64) was found to increase the production. This is the first report that delivers the higher yield of laccase produced from B. subtilis MTCC 2414 using agroresidues as a potential substrate.

Fungal laccases and their applications in bioremediation

Laccases are blue multicopper oxidases, which catalyze the monoelectronic oxidation of a broad spectrum of substrates, for example, ortho- and para-diphenols, polyphenols, aminophenols, and aromatic or aliphatic amines, coupled with a full, four-electron reduction of O₂ to H₂O. Hence, they are capable of degrading lignin and are present abundantly in many white-rot fungi. Laccases decolorize and detoxify the industrial effluents and help in wastewater treatment. They act on both phenolic and nonphenolic lignin-related compounds as well as highly recalcitrant environmental pollutants, and they can be effectively used in paper and pulp industries, textile industries, xenobiotic degradation, and bioremediation and act as biosensors. Recently, laccase has been applied to nanobiotechnology, which is an increasing research field, and catalyzes electron transfer reactions without additional cofactors. Several techniques have been developed for the immobilization of biomolecule such as micropatterning, self-assembled monolayer, and layer-by-layer techniques, which immobilize laccase and preserve their enzymatic activity. In this review, we describe the fungal source of laccases and their application in environment protection.

Partial purification and characterization of a novel extracellular tyrosinase from Auricularia auricula

Extracellular tyrosinase from Auricularia auricula RF201 was purified in a three-step procedure involving ammonium sulfate precipitation, Sephadex G-100, and DEAE-Sepharose column chromatography. The partially purified enzyme showed a single protein band of 12.6 kDa on SDS-PAGE. The optimum pH for tyrosinase activity was 7, and the enzyme was stable between pH 6 and 9. Tyrosinase has optimal activity at 40 °C and retained most of its activity between 4 and 50 °C. A. auricula tyrosinase could oxidize L-tyrosine, L-DOPA, catechol, and caffeic acid and displayed dark brown or peach color. However, the enzyme was unable to catalyze L-phenylalanine and ferulic acid. In comparison with other substrates, L-tyrosine displayed the highest affinity (K m of 0.11 mM) and the maximal reaction velocity (V max of 102.58 μmol/min). Tyrosinase activity was reduced in the presence of numerous tested compounds. Particularly SDS, it significantly inhibited enzyme activity. CuSO4 and NaCl showed an activation effect on enzyme activity, with the maximum activation found in the presence of CuSO4.

Enhancement of catalysis and functional expression of a bacterial laccase by single amino acid replacement

Structure-function relationships underlying laccases properties are very limited that makes these enzymes interesting for protein engineering approaches. Therefore in the current study, a thermostable laccase that was isolated from Bacillus sp. HR03 with the ability of bilirubin oxidation besides its laccase and tyrosinase activity is used. The extensive application of this enzyme is limited by its low expression level in Escherichia coli. Based on sequence alignments and structural studies, three single amino acid substitutions, D500G, D500E, D500S and a glycine insertion, are introduced using site-directed mutagenesis to evaluate the role of Asp(500) located in the C-terminal segment close to the T1 copper center. Substitution of aspartic acid with less sterically hindered, conserved residue such as glycine increase kcat (2.3 fold) and total activity (7.3 fold) which is accompanied by a significant increase in the expression level up to 3 fold. Biochemical characterization and structural studies using far-UV CD and fluorescence spectroscopy reveal the importance of C-terminal copper-binding loop in the laccase functional expression and catalytic efficiency. Kinetic characterization of the purified mutants toward 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), syringaldazine (SGZ) and bilirubin, shows that substrate specificity is left unchanged.

The Determination of Assay for Laccase of Bacillus subtilis WPI with Two Classes of Chemical Compounds as Substrates

Ligninolytic enzyme complexes are involved in lignin degradation. Among them laccases are outstanding because they use molecular oxygen as a co-substrate instead of hydrogen peroxide as used by peroxidases. Bacterial laccase of Bacillus genus was first reported in Claus and Filip (Microbiol Res 152:209-216, 1997), since then more bacterial laccases have been found. In this research, laccase-producing bacteria were screened from pulp and paper industry wastewater, bagass and sugarcane rhizosphere. Nutrient agar medium containing 0.5 mM of guaiacol was used. It was observed that the laccase-producing strains developed brown colour from which 16 strains of Bacillus were identified. One of the isolated strains was identified as Bacillus subtilis WPI based on the results of biochemical tests and 16S rDNA sequence analysis. This strain showed laccase-like activity towards the oxidizing substrates ABTS and guaiacol. In this study guaiacol was used as the substrate of laccase activity assay. For determination of laccase activity of this isolate guaiacol was used as a substrate of assay for the first time in this study. SDS-PAGE and Native-PAGE confirmed the presence of laccase.

Enhanced expression of a recombinant bacterial laccase at low temperature and microaerobic conditions: purification and biochemical characterization

Laccases (benzenediol oxygen oxidoreductase; EC 1.10.3.2) have many biotechnological applications because of their oxidation ability towards a wide range of phenolic compounds. Within recent years, researchers have been highly interested in the identification and characterization of laccases from bacterial sources. In this study, we have isolated and cloned a gene encoding laccase (CotA) from Bacillus sp. HR03 and then expressed it under microaerobic conditions and decreased temperature in order to obtain high amounts of soluble protein. The laccase was purified and its biochemical properties were investigated using three common laccase substrates, 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid) (ABTS), syringaldazine (SGZ) and 2,6-dimethoxyphenol (2,6-DMP). K(M) and k(cat) were calculated 535 microM and 127 s(-1) for ABTS, 53 microM and 3 s(-1) for 2, 6-DMP and 5 microM and 20 s(-1) for SGZ when the whole reactions were carried out at room temperature. Laccase activity was also studied when the enzyme was preincubated at 70 and 80 degrees C. With SGZ as the substrate, the activity was increased three-fold after 50 min preincubation at 70 degrees C and 2.4-fold after 10 min preincubation at 80 degrees C. Preincubation of the enzyme in 70 degrees C for 30 min raised the activity four-fold with ABTS as the substrate. Also, L-dopa was used as a substrate. The enzyme was able to oxidize L-dopa with the K(M) and k(cat) of 1,493 microM and 194 s(-1), respectively.