Production, purification and partial characterisation of a novel laccase from the white-rot fungus Panus tigrinus CBS 577.79

Production, purification, and characterization of p-diphenol oxidase (PDO) enzyme from lignolytic fungal isolate Schizophyllum commune MF-O5

Fungi are producers of lignolytic extracellular enzymes which are used in industries like textile, detergents, biorefineries, and paper pulping. This study assessed for the production, purification, and characterization of novel p-diphenol oxidase (PDO; laccase) enzyme from lignolytic white-rot fungal isolate. Fungi samples collected from different areas of Pakistan were initially screened using guaiacol plate method. The maximum PDO producing fungal isolate was identified on the basis of ITS (internal transcribed spacer sequence of DNA of ribosomal RNA) sequencing. To get optimum enzyme yield, various growth and fermentation conditions were optimized. Later PDO was purified using ammonium sulfate precipitation, size exclusion, and anion exchange chromatography and characterized. It was observed that the maximum PDO producing fungal isolate was Schizophyllum commune (MF-O5). Characterization results showed that the purified PDO was a monomeric protein with a molecular mass of 68 kDa and showed stability at lower temperature (30 °C) for 1 h. The Km and Vmax values of the purified PDO recorded were 2.48 mM and 6.20 U/min. Thermal stability results showed that at 30 °C PDO had 119.17 kJ/K/mol Ea value and 33.64 min half-life. The PDO activity was stimulated by Cu2+ ion at 1.0 mM showing enhanced activity up to 111.04%. Strong inhibition effect was noted for Fe2+ ions at 1 mM showing 12.04% activity. The enzyme showed stability against 10 mM concentration oxidizing reducing agents like DMSO, EDTA, H2O2, NaOCl, and urea and retained more than 75% of relative activity. The characterization of purified PDO enzyme confirmed its tolerance against salt, metal ions, organic solvents, and surfactants indicating its ability to be used in the versatile commercial applications.

Simultaneous Biological Pretreatment and Saccharification of Rice Straw by Ligninolytic Enzymes from Panus neostrigosus I9 and Commercial Cellulase

The utilization of rice straw for biofuel production is limited by its composition. The pretreatment process is required to improve the enzymatic accessibility of polysaccharides in the biomass prior to enzymatic saccharification. In this study, simultaneous biological pretreatment and saccharification (SPS) of rice straw starting from laccase production by Panus neostrigosus I9 was operated in a 2-L fermenter. It was found that fungal physiology was strongly influenced by the agitation, and that the highest laccase production was obtained at an agitation speed of 750 rpm (209.96 ± 0.34 U/L). The dilution rate of 0.05 h-1 was set in continuous fermentation which resulted in laccase activity of 678.49 ± 20.39 U/L, approximately three times higher than that in batch culture. Response surface methodology (RSM) was applied to achieve the condition for maximum percentage of delignification. The maximum percentage of delignification of 45.55% was accomplished after pretreatment of rice straw with laccase enzyme 39.40 U/g rice straw at 43.70 °C for 11.19 h. Reducing sugar of 3.85 ± 0.15 g/L was obtained from the digested rice straw in a SPS reactor, while non-pretreated rice straw gave only 1.13 ± 0.10 g/L within 12 h of incubation. The results indicated that simultaneous biological pretreatment and saccharification (SPS) of rice straw by laccase helped to improve the accessibility of cellulose by cellulolytic enzymes.

Mushroom Ligninolytic Enzymes―Features and Application of Potential Enzymes for Conversion of Lignin into Bio-Based Chemicals and Materials

Mushroom ligninolytic enzymes are attractive biocatalysts that can degrade lignin through oxido-reduction. Laccase, lignin peroxidase, manganese peroxidase, and versatile peroxidase are the main enzymes that depolymerize highly complex lignin structures containing aromatic or aliphatic moieties and oxidize the subunits of monolignol associated with oxidizing agents. Among these enzymes, mushroom laccases are secreted glycoproteins, belonging to a polyphenol oxidase family, which have a powerful oxidizing capability that catalyzes the modification of lignin using synthetic or natural mediators by radical mechanisms via lignin bond cleavage. The high redox potential laccase within mediators can catalyze the oxidation of a wide range of substrates and the polymerization of lignin derivatives for value-added chemicals and materials. The chemoenzymatic process using mushroom laccases has been applied effectively for lignin utilization and the degradation of recalcitrant chemicals as an eco-friendly technology. Laccase-mediated grafting has also been employed to modify lignin and other polymers to obtain novel functional groups able to conjugate small and macro-biomolecules. In this review, the biochemical features of mushroom ligninolytic enzymes and their potential applications in catalytic reactions involving lignin and its derivatives to obtain value-added chemicals and novel materials in lignin valorization are discussed.

Optimized production, purification and molecular characterization of fungal laccase through Alternaria alternata

Objective

Industrial effluents and agriculture biomass are main environmental hazards which are facing by developing country like Pakistan. Along with various other industrial applications, laccases are also involved in the oxidation of various industrial hazardous compounds to detoxify them. This study was designed to produce and purify laccase from ascomyceteous fungi, i.e. Alternaria alternata through solid stat fermentation.

Materials and methods

Abundantly available Sarkanda grass “Saccharum spontaneum” was used as agro-waste substrate for laccase production from fungus A. alternata. Previously only white rot fungi are familiar for laccase production and almost no work has been done on laccase production by A. alternata. In this research work, different physical and chemical parameters were optimized for maximum laccase production through solid state fermentation (SSF).

Results

Enzyme was purified and its molecular weight was determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). Maximum laccase activity (21.87±0.0115 unit/mL) was detected on 7th day of incubation having pH 5 of the medium at 35°C. None of the added metal ions increased laccase production. Galactose and “yeast extract” used as optimum carbon and nitrogen source for highest laccase production.

Conclusion

A monomeric protein (laccase) having approximately 51 kDa molecular weight obtained after SDS-PAGE.

Linking Enzymatic Oxidative Degradation of Lignin to Organics Detoxification

The major enzymes involved in lignin degradation are laccase, class II peroxidases (lignin peroxidase, manganese peroxidase, and versatile peroxidase) and dye peroxidase, which use an oxidative or peroxidative mechanism to deconstruct the complex and recalcitrant lignin. Laccase and manganese peroxidase directly oxidize phenolic lignin components, while lignin peroxidase and versatile peroxidase can act on the more recalcitrant non-phenolic lignin compounds. Mediators or co-oxidants not only increase the catalytic ability of these enzymes, but also largely expand their substrate scope to those with higher redox potential or more complicated structures. Neither laccase nor the peroxidases are stringently selective of substrates. The promiscuous nature in substrate preference can be employed in detoxification of a range of organics.

Ligninolytic enzymes: Versatile biocatalysts for the elimination of endocrine-disrupting chemicals in wastewater

Direct municipal wastewater effluent discharge from treatment plants has been identified as the major source of endocrine‐disrupting chemicals (EDC) in freshwaters. Consequently, efficient elimination of EDC in wastewater is significant to good water quality. However, conventional wastewater treatment approaches have been deficient in the complete removal of these contaminants. Hence, the exploration of new and more efficient methods for elimination of EDC in wastewater is imperative. Enzymatic treatment approach has been suggested as a suitable option. Nonetheless, ligninolytic enzymes seem to be the most promising group of enzymes for EDC elimination, perhaps, owing to their unique catalytic properties and characteristic high redox potentials for oxidation of a wide spectrum of organic compounds. Therefore, this paper discusses the potential of some ligninolytic enzymes (laccase, manganese peroxidase, and versatile peroxidase) in the elimination of EDC in wastewater and proposes a new scheme of wastewater treatment process for EDC removal.

Kinetic analysis and structural studies of a high-efficiency laccase from Cerrena sp. RSD1

A high‐efficiency laccase, DLac, was isolated from Cerrena sp. RSD1. The kinetic studies indicate that DLac is a diffusion‐limited enzyme. The crystal structure of DLac was determined to atomic resolution, and its overall structure shares high homology to monomeric laccases, but displays unique substrate‐binding loops from those in other laccases. The substrate‐binding residues with small side chain and the short substrate‐binding loop IV broaden the substrate‐binding cavity and may facilitate large substrate diffusion. Unlike highly glycosylated fungal laccases, the less‐glycosylated DLac contains one highly conserved glycosylation site at N432 and an unique glycosylation site at N468. The N‐glycans stabilize the substrate‐binding loops and the protein structure, and the first N‐acetylglucosamine is crucial for the catalytic efficiency. Additionally, a fivefold increase in protein yield is achieved via the submerged culture method for industrial applications.

Database

The atomic coordinates of the structure of DLac from Cerrena sp. RSD1 and structural factors have been deposited in the RCSB Protein Data Bank (PDB ID: 5Z1X).

Removal of pharmaceutical compounds in water and wastewater using fungal oxidoreductase enzymes

Due to recalcitrance of some pharmaceutically active compounds (PhACs), conventional wastewater treatment is not able to remove them effectively. Therefore, their occurrence in surface water and potential environmental impact has raised serious global concern. Biological transformation of these contaminants using white-rot fungi (WRF) and their oxidoreductase enzymes has been proposed as a low cost and environmentally friendly solution for water treatment. The removal performance of PhACs by a fungal culture is dependent on several factors, such as fungal species, the secreted enzymes, molecular structure of target compounds, culture medium composition, etc. In recent 20 years, numerous researchers tried to elucidate the removal mechanisms and the effects of important operational parameters such as temperature and pH on the enzymatic treatment of PhACs. This review summarizes and analyzes the studies performed on PhACs removal from spiked pure water and real wastewaters using oxidoreductase enzymes and the data related to degradation efficiencies of the most studied compounds. The review also offers an insight into enzymes immobilization, fungal reactors, mediators, degradation mechanisms and transformation products (TPs) of PhACs. In brief, higher hydrophobicity and having electron-donating groups, such as amine and hydroxyl in molecular structure leads to more effective degradation of PhACs by fungal cultures. For recalcitrant compounds, using redox mediators, such as syringaldehyde increases the degradation efficiency, however they may cause toxicity in the effluent and deactivate the enzyme. Immobilization of enzymes on supports can enhance the performance of enzyme in terms of reusability and stability. However, the immobilization strategy should be carefully selected to reduce the cost and enable regeneration. Still, further studies are needed to elucidate the mechanisms involved in enzymatic degradation and the toxicity levels of TPs and also to optimize the whole treatment strategy to have economical and technical competitiveness.

Enzyme-based solutions for textile processing and dye contaminant biodegradation-a review

The textile industry, as recognized conformist and stake industry in the world's economy, is facing serious environmental challenges. In numerous industries, in practice, various chemical-based processes from initial sizing to final washing are fascinating harsh environment concerns. Some of these chemicals are corrosive to equipment and cause serious damage itself. Therefore, in the twenty-first century, chemical and allied industries quest a paradigm transition from traditional chemical-based concepts to a greener, sustainable, and environmentally friendlier catalytic alternative, both at the laboratory and industrial scales. Bio-based catalysis offers numerous benefits in the context of biotechnological industry and environmental applications. In recent years, bio-based processing has received particular interest among the scientist for inter- and multi-disciplinary investigations in the areas of natural and engineering sciences for the application in biotechnology sector at large and textile industries in particular. Different enzymatic processes such as chemical substitution have been developed or in the process of development for various textile wet processes. In this context, the present review article summarizes current developments and highlights those areas where environment-friendly enzymatic textile processing might play an increasingly important role in the textile industry. In the first part of the review, a special focus has been given to a comparative discussion of the chemical-based "classical/conventional" treatments and the modern enzyme-based treatment processes. Some relevant information is also reported to identify the major research gaps to be worked out in future.

Induction, purification, and characterization of a thermo and pH stable laccase from Abortiporus biennis J2 and its application on the clarification of litchi juice

A fungus J2 producing laccase with high yield was screened in soils and identified as Abortiporus biennis. The production of laccase was induced by 0.1 mM Cu²⁺, 0.1 mM tannic acid, and 0.5 M ethanol. The laccase from Abortiporus biennis J2 was purified to electrophoretic homogeneity by a couple of steps. The N-terminal amino acid sequence of the enzyme was AIGPTADLNISNADI. The properties of the purified laccase were investigated. The result showed the laccase from Abortiporus biennis J2 is a thermo and pH stable enzyme. The laccase activity was inhibited by Hg²⁺, Cd²⁺, Fe²⁺, Ag⁺, Cu²⁺, and Zn²⁺, while promoted by Mg²⁺, Mn²⁺ at 10 mM level. Purified laccase was used to the clarification of litchi juice. After treatment with this laccase, the phenolic content of litchi juice had been found to be greatly reduced along with an increase in the clarity of the juice. The result indicated the potential of this laccase for application in juice procession.

Conditions Optimizing and Application of Laccase-mediator System (LMS) for the Laccase-catalyzed Pesticide Degradation

A high capacity of laccase from Trametes versicolor capable of degrading pesticides has been revealed. The conditions for degrading of five selected pesticides including chlorpyrifos, chlorothalonil, pyrimethanil, atrazine and isoproturon with the purified laccases from Trametes versicolor were optimized. The results showed that the optimum conditions for the highest activity were pH at 5.0 and temperature at 25 °C. The best mediators were violuric acid for pyrimethanil and isoproturon, vanillin for chlorpyrifos, and acetosyringone and HBT for chlorothalonil and atrazine, respectively. The laccase was found to be stable at a pH range from 5.0 to 7.0 and temperature from 25 to 30 °C. It was observed that each pesticide required a different laccase mediator concentration typically between 4.0-6.0 mmol/L. In the experiment, the degradation rates of pyrimethanil and isoproturon were significantly faster than those of chlorpyrifos, chlorothalonil and atrazine. For example, it was observed that pyrimethanil and isoproturon degraded up to nearly 100% after 24 hours while the other three pesticides just reached up 90% of degradation after 8 days of incubation.

The comparative study of a laccase-natural clinoptilolite-based catalyst activity and free laccase activity on model compounds

For the first time a laccase from Trametes versicolor was immobilized on a natural clinoptilolite with Si/Al=5 to obtain a biocatalyst for environmental applications. Immobilization procedures exploiting adsorption and covalent binding were both tested, and only the last provided enough activity for practical applications. The optimal conditions for the immobilization of the enzyme on the support and the kinetic parameters for the free and covalent bonded laccase were determined. The laccase bonded to the zeolitic support showed a lower activity than the free laccase, but the pH and thermal stability were greater. 20 mg of dry biocatalyst containing 1 U of laccase were able to remove in 50h 73-78% of 2-chlorophenol and 2,4-dichlorophenol in relatively concentrated aqueous solutions (100 μmol L(-1)).

Chlorobenzoic acid degradation by Lentinus (Panus) tigrinus: in vivo and in vitro mechanistic study-evidence for P-450 involvement in the transformation

Aim of this work was to investigate the ability of Lentinus (Panus) tigrinus to degrade and detoxify a chlorobenzoate (CBA) mixture composed of mono-, di- and tri-chlorinated isomers. The degradation process was investigated as a function of both the growing medium (i.e. low N Kirk's and malt extract-glucose medium) and cultivation conditions (i.e. stationary and shaken cultures). The majority of CBAs were quantitatively degraded within the early 15 d from spiking with the notable exception of the double ortho-chlorinated compounds, 2,6-di-, 2,3,6-tri- and 2,4,6-tri-CBA. Analysis of the degradation intermediates indicated the occurrence of side chain reduction, hydroxylation and methylation reactions. Although CBAs stimulated laccase production, in vitro experiments with a purified L. tigrinus laccase isoenzyme demonstrated its inability to participate in the initial attack on CBAs even in the presence of redox mediators; similar results were found with a Mn-peroxidase isoenzyme. Conversely, prompt degradation was observed upon 1h incubation of CBAs with a purified microsomal fraction containing cytochrome P-450 monooxygenase. The nature of some reaction products (i.e. hydroxylated derivatives), the dependency of the reaction on NADPH and its susceptibility to either CO or piperonyl butoxide inhibition confirmed the involvement of L. tigrinus cytochrome P-450 in the early steps of CBA degradation.

Microbial enzymes with special characteristics for biotechnological applications

This article overviews the enzymes produced by microorganisms, which have been extensively studied worldwide for their isolation, purification and characterization of their specific properties. Researchers have isolated specific microorganisms from extreme sources under extreme culture conditions, with the objective that such isolated microbes would possess the capability to bio-synthesize special enzymes. Various Bio-industries require enzymes possessing special characteristics for their applications in processing of substrates and raw materials. The microbial enzymes act as bio-catalysts to perform reactions in bio-processes in an economical and environmentally-friendly way as opposed to the use of chemical catalysts. The special characteristics of enzymes are exploited for their commercial interest and industrial applications, which include: thermotolerance, thermophilic nature, tolerance to a varied range of pH, stability of enzyme activity over a range of temperature and pH, and other harsh reaction conditions. Such enzymes have proven their utility in bio-industries such as food, leather, textiles, animal feed, and in bio-conversions and bio-remediations.

New bacteria Bacillus nitroreducens PLC9 with hydrogen peroxide-degrading activity with high survival rate in hydrogen peroxide

Bacteria were isolated from wastewater containing highly concentrated hydrogen peroxide that had been used to clean the pure water delivery system in a semiconductor plant. One bacterium was selected for its high hydrogen peroxide degradation activity. In the presence of 1% hydrogen peroxide, it degraded 72.5% in 5 min. It showed 100% viability after 6 h at 1% hydrogen peroxide. Even at 3% hydrogen peroxide, it survived for more than 6 h. This bacterium was named as Bacillus nitroreducens PLC9 since its 16S rRNA showed 100% similarity with the recently reported new species B. nitroreducens. Purified catalase from B. nitroreducens PLC9 was characterized as a thermo-alkali-stable hydroperoxidase type II catalase, and it is suggested as a new type of catalase based on following: (1) it is stable over a broad pH range (pH 4-11); (2) it is consisted of homodimers with a molecular weight of 66 kDa (total molecular weight, 134 kDa); (3) its activity was not inhibited by 3-amino-1,2,4-triazole; and (4) its N-terminal sequence has never been reported before. Both B. nitroreducens PLC9 and the isolated catalase can be used for efficient degradation of hydrogen peroxide at high concentrations.

Enhanced enzymatic hydrolysis of rice straw by removal of phenolic compounds using a novel laccase from yeast Yarrowia lipolytica

An extracellular laccase-producing yeast was isolated from soil and identified as Yarrowia lipolytica by its morphology and by comparison of its internal transcribed spacer rDNA gene sequence. Extracellular laccase (YlLac) from Y. lipolytica was purified to homogeneity by anion-exchange and gel filtration chromatography. YlLac is a monomeric glycoprotein with 14% carbohydrate content and a molecular mass of 67kDa. It showed a higher catalytic efficiency towards 2,2'-Azino-bis (3-ethylbenzthiazoline-6-sulfonic acid) (k(cat)/K(m)=19.3s(-1)μM(-1)) and 2,6-dimethoxyphenol (k(cat)/K(m)=13s(-1)μM(-1)) than any other reported laccase. This enzyme was able to oxidize phenolic compounds present in pretreated rice straw. Several parameters (temperature, enzyme concentration, and mediator compounds) to enhance removal of phenolic compounds from pretreated rice straw were optimized using response surface methodology. The use of YlLac for the removal of cellulase inhibitory compounds from biomass slurries was found to be a promising approach for improving the efficiency of biorefineries.

Biochemical characterization of a novel laccase from the basidiomycete fungus Cerrena sp. WR1

This study reports a new white-rot fungus Cerrena sp. WR1, identified based on an 18S rDNA sequence, which can secrete extracellular forms of laccase with a maximal activity reaching 202 000 U l⁻¹ in a 5-l fermenter. A laccase protein, designated Lcc3, was purified and shown to be N-linked glycosylated by PNGase F and liquid chromatography tandem mass spectrometry analyses. The respective full-length cDNA gene (lcc3) of the Lcc3 protein was obtained using polymerase chain reaction-based methods. Kinetic studies showed that the K(m) and k(cat) of the native Lcc3 were 3.27 μM and 934.6 s⁻¹ for 2,2'-Azino-bis-(3-ethylbenzthiazoline-6-sulfonic acid), 849.1 μM and 147.9 s⁻¹ for guaiacol, 392.7 μM and 109.2 s⁻¹ for 2,6-dimethoxyphenol, and 881 μM and 115.5 s⁻¹ for catechol, respectively. The T(m) of Lcc3 was determined at 73.9°C and it showed a long t(½) (120 min) at 50°C. The laccase was highly ethanol resistant, with 80% of its original activity was detected when incubated in 25% ethanol for 14 days. Furthermore, crude enzyme broth or Lcc3 could degrade lignin in kraft paper (26.5%), and showed high decoloration efficiency (90%) on synthetic dye Remazol Brilliant Blue R. Together, these data demonstrate that Cerrena sp. WR1 Lcc3 possesses novel biochemical and kinetic properties that may aid its application in industry.

Bioligninolysis: recent updates for biotechnological solution

Bioligninolysis involves living organisms and/or their products in degradation of lignin, which is highly resistant, plant-originated polymer having three-dimensional network of dimethoxylated (syringyl), monomethoxylated (guaiacyl), and non-methoxylated (p-hydroxyphenyl) phenylpropanoid and acetylated units. As a major repository of aromatic chemical structures on earth, lignin bears paramount significance for its removal owing to potential application of bioligninolytic systems in industrial production. Early reports illustrating the discovery and cloning of ligninolytic biocatalysts in fungi was truly a landmark in the field of enzymatic delignification. However, the enzymology for bacterial delignification is hitherto poorly understood. Moreover, the lignin-degrading bacterial genes are still unknown and need further exploration. This review deals with the current knowledge about ligninolytic enzyme families produced by fungi and bacteria, their mechanisms of action, and genetic regulation and reservations, which render them attractive candidates in biotechnological applications.

Biological degradation of anthroquinone and azo dyes by a novel laccase from Lentinus sp

This study identifies a new fungal strain, Lentinus sp., that can produce extracellular forms of laccases with an activity of approximately 58 300 U/L. A purified laccase (designated lcc3) was identified by LC-ESI MS/MS as an N-linkage glycosylated protein. The isolated lcc3 cDNA is composed of 1563 bp encoding for a polypeptide of 521 amino acid residues with 4 putative Cu binding regions. Kinetic analyses revealed that the specific activity, k(cat), K(m), and k(cat)/K(m) of lcc3 at pH 2.5 and 70 °C with 2,2'-azino-bis-(3-ethylbenzthiazoline-6-sulfonic acid) used as a substrate was 2047 U mg(-1), 2017 s(-1), 8.4 μM, and 240 s(-1) μM(-1), respectively. Lcc3 is stable at pH 6.0-10.0 and has a midpoint temperature (T(m)) of 77.1 °C. We observed 97% decolorization efficiency on Acid Blue 80, 88% on RBBR, and 61% on Acid Red 37 by lcc3. Structural modeling analysis showed that five, four, and three hydrogen bonds can be formed between Acid Blue 80 and Arg(178), Arg(182), or Asn(358); between RBBR and His(132), Ser(134), or Asp(482); and between Acid Red 37 and Arg(178), respectively. Notably, Lentinus lcc3 efficiently reversed the toxicity of anthraquinone and azo dyes on rice seed germination and decolorized industrial textile effluent, suggesting the enzyme may be valuable for bioremediation.

A laccase with HIV-1 reverse transcriptase inhibitory activity from the broth of mycelial culture of the mushroom Lentinus tigrinus

A 59 kDa laccase with inhibitory activity against HIV-1 reverse transcriptase (IC₅₀ = 2.4 μM) was isolated from the broth of mycelial culture of the mushroom Lentinus tigrinus. The isolation procedure involved ion exchange chromatography on DEAE-cellulose and CM-cellulose, and gel filtration by fast protein liquid chromatography on Superdex 75. The laccase was adsorbed on both types of ion exchangers. About 95-fold purification was achieved with a 25.9% yield of the enzyme. The procedure resulted in a specific enzyme activity of 76.6 U/mg. Its N-terminal amino acid sequence was GIPDLHDLTV, which showed little similarity to other mushroom laccase and other Lentinus tigrinus strain laccase. Its characteristics were different from previously reported laccase of other Lentinus tigrinus strain. Maximal laccase activity was observed at a pH of 4 and at a temperature of 60°C, respectively. This study yielded the information about the potentially exploitable activities of Lentinus tigrinus laccase.

Redox potentials, laccase oxidation, and antilarval activities of substituted phenols

Laccases are copper-containing oxidases that are involved in sclerotization of the cuticle of mosquitoes and other insects. Oxidation of exogenous compounds by insect laccases may have the potential to produce reactive species toxic to insects. We investigated two classes of substituted phenolic compounds, halogenated di- and trihydroxybenzenes and substituted di-tert-butylphenols, on redox potential, oxidation by laccase and effects on mosquito larval growth. An inverse correlation between the oxidation potentials and laccase activity of halogenated hydroxybenzenes was found. Substituted di-tert-butylphenols however were found to impact mosquito larval growth and survival. In particular, 2,4-di-tert-butyl-6-(3-methyl-2-butenyl)phenol (15) caused greater than 98% mortality of Anophelesgambiae larvae in a concentration of 180nM, whereas 2-(3,5-di-tert-butyl-4-hydroxyphenyl)-2-methylpropanal oxime (13) and 6,8-di-tert-butyl-2,2-dimethyl-3,4-dihydro-2H-chromene (33) caused 93% and 92% mortalities in concentrations of 3.4 and 3.7μM, respectively. Larvae treated with di-tert-butylphenolic compounds died just before pupation.

Lignolytic Enzymes of a Mushroom Stereum ostrea Isolated from Wood Logs

Production of lignolytic enzymes by the mushroom fungus Stereum ostrea in liquid medium under conditions of vegetative growth was examined for 10 days in comparison to the reference culture Phanerochaete chrysosporium. Though growth and secretion of extracellular protein by S. ostrea were comparable to those of P. chrysosporium, yields of laccase enzyme by S. ostrea were higher than laccase titres of P. chrysosporium by more than 2 folds on the peak production time interval (IVth day of incubation). S. ostrea yielded titres of 25 units of laccase/ml as against 8.9 units of laccase/ml on the IVth day of incubation. Stereum ostrea also exhibited activities of other lignolytic enzymes, lignin peroxidase (LiP) and manganese peroxidase (MnP), higher than the reference culture. Growth of S. ostrea on the medium in the presence of Remazol orange 16 resulted in the decolourisation of dye, confirming the presence of lignolytic enzymes. S. ostrea appears to be a promising culture with complete lignolytic system.

In vivo and in vitro polycyclic aromatic hydrocarbons degradation by Lentinus (Panus) tigrinus CBS 577.79

The ability of stationary and shaken Lentinus tigrinus CBS 577.79 liquid cultures to degrade a mixture of polycyclic aromatic hydrocarbons (PAHs) in N-rich (i.e., malt extract glucose, MEG) and in N-limited (low-N Kirk's medium, LNKM) media was investigated. Best results were obtained in shaken cultures where PAHs were degraded by 91% and 97% in MEG and LNKM, respectively; in stationary cultures, on the contrary, the degradation was never higher than 50%. Laccase activity was predominant on MEG while Mn-peroxidase (MnP) was preferentially produced in LNKM. The identification of degradation products showed the presence of several PAH derivatives, such as quinones, dicarboxylated and ring fission derivatives, presumably derived from the action of lignin-modifying enzymes. The presence of some degradation products (e.g., hydroxylated derivatives of anthrone and phenanthrene 9,10-dihydrodiol) suggested the possible involvement of cytochrome P-450-epoxide hydrolase system, the active form of which was found in 7-day-old cultures on MEG. In vitro experiments showed that the MnP from L. tigrinus had wider PAH substrate range and higher oxidation ability than the laccase produced by the same strain.

Directed evolution of copper nitrite reductase to a chromogenic reductant

Directed evolution methods were developed for Cu-containing nitrite reductase (NiR) from Alcaligenes faecalis S-6. The PCR cloning strategy allows for the efficient production of libraries of 100 000 clones by a modification of a megaprimer-based whole-plasmid synthesis reaction. The high-throughput screen includes colony lift onto a nylon membrane and subsequent lysis of NiR-expressing colonies in the presence of Cu(2+) ions for copper incorporation into intracellularly expressed NiR. Addition of a chromogenic substrate, 3, 3'-diaminobenzidine (DAB), results in deposition of red, insoluble color at the site of oxidation by functional NiR. Twenty-thousand random variants of NiR were screened for improved function with DAB as a reductant, and five variants were identified. These variants were shuffled and screened, yielding two double variants. An analog of the DAB substrate, o-dianisidine, which is oxidized to a water-soluble product was used for functional characterization. The double variant M150L/F312C was most proficient at o-dianisidine oxidation with dioxygen as the electron acceptor (5.5X wt), and the M150L single variant was most proficient at o-dianisidine oxidation with nitrite as the electron acceptor (8.5X wt). The library generation and screening method can be employed for evolving new reductase functions in NiR and for screening of efficient folding of engineered NiRs.

LccA, an archaeal laccase secreted as a highly stable glycoprotein into the extracellular medium by Haloferax volcanii

Laccases couple the oxidation of phenolic compounds to the reduction of molecular oxygen and thus span a wide variety of applications. While laccases of eukaryotes and bacteria are well characterized, these enzymes have not been described in archaea. Here, we report the purification and characterization of a laccase (LccA) from the halophilic archaeon Haloferax volcanii. LccA was secreted at high levels into the culture supernatant of a recombinant H. volcanii strain, with peak activity (170 +/- 10 mU.ml(-)(1)) at stationary phase (72 to 80 h). LccA was purified 13-fold to an overall yield of 72% and a specific activity of 29.4 U.mg(-)(1) with an absorbance spectrum typical of blue multicopper oxidases. The mature LccA was processed to expose an N-terminal Ala after the removal of 31 amino acid residues and was glycosylated to 6.9% carbohydrate content. Purified LccA oxidized a variety of organic substrates, including bilirubin, syringaldazine (SGZ), 2,2,-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), and dimethoxyphenol (DMP), with DMP oxidation requiring the addition of CuSO(4). Optimal oxidation of ABTS and SGZ was at 45 degrees C and pH 6 and pH 8.4, respectively. The apparent K(m) values for SGZ, bilirubin, and ABTS were 35, 236, and 670 muM, with corresponding k(cat) values of 22, 29, and 10 s(-)(1), respectively. The purified LccA was tolerant of high salt, mixed organosolvents, and high temperatures, with a half-life of inactivation at 50 degrees C of 31.5 h.

"Blue" laccases

This review concerns copper-containing oxidases--laccases. Principal biochemical and electrochemical properties of laccases isolated from different sources are described, as well as their structure and mechanism of catalysis. Possible applications of laccases in different fields of biotechnology are discussed.

Decolorization of cotton pulp black liquor by pleurotus ostreatus in a bubble-column reactor

Decolorization of cotton pulp black liquor by Pleurotus ostreatus B1 in a bubble-column reactor (BCR) was studied. The optimal conditions for the running of BCR are 30 degrees C, pH 6.0, aeration rate 1.2 L min(-1), and mycelial age 7 days. Under the optimal conditions, the BCR was run for four cycles (each cycle, 12 days) and the same mycelial pellets were reused. The ultimate decolorization and COD removal rates are 76% and 80%, respectively.