Stabilization of lignin peroxidases in white rot fungi by tryptophan

Synergistic lignin degradation between Phanerochaete chrysosporium and Fenton chemistry is mediated through iron cycling and ligninolytic enzyme induction

Removal of recalcitrant lignin from wastewater remains a critical bottleneck in multiple aspects relating to microbial carbon cycling ranging from incomplete treatment of biosolids during wastewater treatment to limited conversion of biomass feedstock to biofuels. Based on previous studies showing that the white rot fungus Phanerochaete chrysosporium and Fenton chemistry synergistically degrade lignin, we sought to determine optimum levels of Fenton addition and the mechanisms underlying this synergy. We tested the extent of degradation of lignin under different ratios of Fenton reagents and found that relatively low levels of H2O2 and Fe(II) enhanced fungal lignin degradation, achieving 80.4 ± 1.61 % lignin degradation at 1.5 mM H2O2 and 0.3 mM Fe(II). Using a combination of whole-transcriptome sequencing and iron speciation assays, we determined that at these concentrations, Fenton chemistry induced the upregulation of 80 differentially expressed genes in P. ch including several oxidative enzymes. This study underlines the importance of non-canonical, auxiliary lignin-degrading pathways in the synergy between white rot fungi and Fenton chemistry in lignin degradation. We also found that, relative to the abiotic control, P. ch. increases the availability of Fe(II) for the production of hydroxyl radicals in the Fenton reaction by recycling Fe(III) (p < 0.001), decreasing the Fe(II) inputs necessary for lignin degradation via the Fenton reaction.

Strengthening Fenton-like reactions to improve lignocellulosic degradation performance by increasing lignocellulolytic enzyme core microbes during rice straw composting

This study aimed to explore the effect of Fenton-like reactions on lignocellulosic degradation performance and identify their driving factors during composting. Rice straw was pretreated by inoculating Aspergillus fumigatus Z1 and then adding Fe (II), which resulted in Fenton-like reactions. The treatment groups included CK (control), Fe (addition of Fe (II)), Z1 (inoculation of A. fumigatus Z1), and Fe + Z1 (inoculation of A. fumigatus Z1 and addition of Fe (II)). The results suggested that Fenton-like reactions can produce lignocellulolytic enzymes and degrade lignocellulose, due to the variation in microbial community composition and diversity. In addition, functional modular microbes were identified by network analysis, which can produce endoglucanase and xylanase. Regarding ligninase, bacteria were more favorable for producing manganese peroxidase, and fungi were more favorable for producing laccase. Additionally, reducing sugars, organic matter, total nitrogen and amino acids were key microhabitat factors of functional modular bacteria, while organic matter, reducing sugars, amino acids and C/N were key microhabitat factors of functional modular fungi, thereby promoting the degradation of lignocellulose. This study provides technical support for lignocellulosic degradation based on Fenton-like reactions.

Construction of CNC@SiO2@PL Based Superhydrophobic Wood with Excellent Abrasion Resistance Based on Nanoindentation Analysis and Good UV Resistance

Construction of superhydrophobic woods with high abrasion resistance is still a major challenge, and micro analysis for abrasion resistance is scarce. To improve these issues, cellulose nanocrystals (CNC)@SiO₂@phosphorylated lignin (PL) rods were prepared by SiO₂ in situ generated on CNC, and then the modified lignin attached to the CNC@SiO₂ rods surface. Subsequently, the superhydrophobic coating was constructed using hydrophobic modified CNC@SiO₂@PL rods as the main structural substance by simple spraying or rolling them onto wood surfaces, and both polydimethylsiloxane (PDMS) and epoxy resin were used as the adhesives. The resulting coating had excellent superhydrophobic properties with a water contact angle (WCA) of 157.4° and a slide angle (SA) of 6°. The introduced PL could enhance ultraviolet (UV) resistance of the coating due to the presence of these groups that absorbed UV light in lignin. In the abrasion resistance test, compared with the SiO₂/PL coating, the abrasion resistance of the one with CNC was much higher, suggesting that CNC could improve the abrasion resistance of the coating due to its high crystallinity and excellent mechanical strength. The coating with PDMS performed better than the one with epoxy resin because the soft surface could offset part of the external impact by deformation in the abrasion process. This was also consistent with the results of the nanoindentation (NI) tests. In view of the simple preparation and good performance, this superhydrophobic wood will have broad application potential.

Functional Characterization of Melanin Decolorizing Extracellular Peroxidase of Bjerkandera adusta

Melanin pigmentation in the human skin results from complicated cellular mechanisms that remain to be entirely understood. Uneven melanin pigmentation has been counteracted by inhibiting synthesis or transfer of melanin in the skin. Recently, an enzymatic approach has been proposed, wherein the melanin in the skin is decolorized using lignin peroxidase. However, not many enzymes are available for decolorizing melanin; the most studied one is lignin peroxidase derived from a lignin degrading fungus, Phanerochaete chrysosporium. Our current study reveals that versatile peroxidase from Bjerkandera adusta can decolorize synthetic melanin. Melanin decolorization was found to be dependent on veratryl alcohol and hydrogen peroxide, but not on Mn²⁺. The degree of decolorization reached over 40% in 10 min at 37 °C and a pH of 4.5. Optimized storage conditions were slightly different from those for the reaction; crude enzyme preparation was the most stable at 25 °C at pH 5.5. Since the enzyme rapidly lost its activity at 50 °C, stabilizers were screened. As a result, glycerol, a major component in several cosmetic formulations, was found to be a promising excipient. Our results suggest that B. adusta versatile peroxidase can be considered for future cosmetic applications aimed at melanin decolorization.

Synthetic dyes degradation using lignolytic enzymes produced from Halopiger aswanensis strain ABC_IITR by Solid State Fermentation

The present work focuses on studying the degradation of industrial synthetic dyes, which poses serious health hazards and a drastic impact on the environment. Currently available enzymatic processes have higher production and operational costs. However, most enzymes are active at acidic pH, which limits its application in textile dye degradation. This problem can be overcome by lignolytic enzymes obtained from halo-alkaliphile through Solid State Fermentation (SSF) using wheat bran (agro-byproduct) as a substrate. The major lignolytic enzymes studied were Lignin Peroxidase (LiP), Manganese Peroxidase (MnP), and laccase. The results demonstrated the highest activity of 215.4 ± 1.57 of LiP, 36.8 ± 2.38 of MnP, and 8.34 ± 0.21 IU/gds of laccase. Crude enzymes were used to treat synthetic dyes (mainly azo dyes), and their potential for its degradation was confirmed by spectrophotometric, GC-MS, and HPLC analysis. The highest decolorization of 82-93% of Malachite Green (MG) was achieved in LiP and MnP mediated reaction system within 2 hours. The laccase reaction system showed degradation of 53.87% of methyl orange without adding any redox mediator. After obtaining these results, the crude LiP and MnP in the reaction system were further subjected to decolorization at a higher MG concentration of 100-600 mg/L without a redox mediator. As a result, both LiP and MnP decolorized MG by 72-89%. Further, GC-MS analysis of MG biodegradation products confirmed the formation of less toxic low molecular weight products such as benzaldehyde and methanone.

Enzyme Activities of Five White-Rot Fungi in the Presence of Nanocellulose

White-rot fungi can degrade all lignocellulose components due to their potent lignin and cellulose-degrading enzymes. In this study, five white-rot fungi, Trametes versicolor, Trametes pubescens, Ganoderma adspersum, Ganoderma lipsiense, and Rigidoporus vitreus were tested for endoglucanase, laccase, urease, and glucose-6-phosphate (G6P) production when grown with malt extract and nanocellulose in the form of TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical) oxidized cellulose nanofibrils (CNF) and cellulose nanocrystals (CNC). Results show that temperature plays a key role in controlling the growth of all five fungi when cultured with malt extract alone. Endoglucanase activities were highest in cultures of G. adspersum and G. lipsiense and laccase activities were highest in cultures of T. versicolor and R. vitreus. Urease activities were highest in cultures of G. adspersum, G. lipsiense, and R. vitreus. Glucose-6-phosphate levels also indicate that cells were actively metabolizing glucose present in the cultures. These results show that TEMPO-oxidized CNF and CNC do not inhibit the production of specific lignocellulose enzymes by these white-rot fungi. The apparent lack of enzymatic inhibition makes TEMPO-oxidized CNF and CNC excellent candidates for future biotechnological applications in combination with the white-rot fungi studied here.

Biodegradation of ciprofloxacin by white rot fungus Pleurotus ostreatus

Unrestricted and reckless use of antibiotics has resulted in their accumulation in environment. This, in turn, has led to the emergence of multiple drug-resistant microbes. The present study focuses on degradation of ciprofloxacin (CIP) by an edible white rot fungus Pleurotus ostreatus. Effect of CIP was determined on radial growth and biomass of P. ostreatus. Titrimetric and spectrophotometric assays were carried out to assess the degrading potential of P. ostreatus towards CIP. It was found that CIP has a stimulatory effect on growth and enzyme activity of P. ostreatus. Maximum enzyme (glucanase, ligninases, laccase) production was observed at the highest concentration of CIP (500 ppm). Antibiotic degradation of about 68.8, 94.25 and 91.34% was estimated after 14 days of incubation at 500 ppm CIP using Titrimetric, Indigo carmine and Methyl orange assay, respectively. Degradation of CIP was further validated by high performance liquid chromatography (HPLC) and microbiological analysis. HPLC analysis revealed 95.07% degradation while microbiological test also exhibited a decreased antimicrobial activity of degraded products against Escherichia coli, Staphylococcus aureus and Streptococcus pyogenes. To the best of our knowledge, this is the first study wherein P. ostreatus was used for the degradation of ciprofloxacin.

Effects of saline-alkaline stress on benzo[a]pyrene biotransformation and ligninolytic enzyme expression by Bjerkandera adusta SM46

Benzo[a]pyrene (BaP) accumulates in marine organisms and contaminated coastal areas. The biotreatment of waste water using saline-alkaline-tolerant white rot fungi (WRF) represents a promising method for removing BaP under saline-alkaline conditions based on WRF's ability to produce ligninolytic enzymes. In a pre-screening for degradation of polycyclic aromatic hydrocarbons of 82 fungal strains using Remazol brilliant blue R, Bjerkandera adusta SM46 exhibited the highest tolerance to saline-alkaline stress. Moreover, a B. adusta culture grown in BaP-containing liquid medium exhibited resistance to salinities up to 20 g l(-1). These conditions did not inhibit fungal growth or the expression of manganese peroxidase (MnP) or lignin peroxidase (LiP). The degradation rate also became higher as salinity increased to 20 g l(-1). Fungal growth and enzyme expression were inhibited at a salinity of 35 g l(-1). These inhibitory effects directly decreased the degradation rate (>24%). The presence of MnSO4 as an inducer improved the degradation rate and enzyme expression. MnP and LiP activity also increased by seven- and fivefold, respectively. SM46 degraded BaP (38-89% over 30 days) in an acidic environment (pH 4.5) and under saline-alkaline stress conditions (pH 8.2). Investigating the metabolites produced revealed BaP-1,6-dione as the main product, indicating the important role of ligninolytic enzymes in initializing BaP cleavage. The other metabolites detected, naphthalene acetic acid, hydroxybenzoic acid, benzoic acid, and catechol, may have been ring fission products. The wide range of activities observed suggests that B. adusta SM46 is a potential agent for biodegrading BaP under saline conditions.

Uncovering the cultivable microbial diversity of costa rican beetles and its ability to break down plant cell wall components

Coleopterans are the most diverse insect order described to date. These organisms have acquired an array of survival mechanisms through their evolution, including highly efficient digestive systems. Therefore, the coleopteran intestinal microbiota constitutes an important source of novel plant cell wall-degrading enzymes with potential biotechnological applications. We isolated and described the cultivable fungi, actinomycetes and aerobic eubacteria associated with the gut of larvae and adults from six different beetle families colonizing decomposing logs in protected Costa Rican ecosystems. We obtained 611 isolates and performed phylogenetic analyses using the ITS region (fungi) and 16S rDNA (bacteria). The majority of fungal isolates belonged to the order Hypocreales (26% of 169 total), while the majority of actinomycetes belonged to the genus Streptomyces (86% of 241 total). Finally, we isolated 201 bacteria spanning 19 different families belonging into four phyla: Firmicutes, α, β and γ-proteobacteria. Subsequently, we focused on microbes isolated from Passalid beetles to test their ability to degrade plant cell wall polymers. Highest scores in these assays were achieved by a fungal isolate (Anthostomella sp.), two Streptomyces and one Bacillus bacterial isolates. Our study demonstrates that Costa Rican beetles harbor several types of cultivable microbes, some of which may be involved in symbiotic relationships that enable the insect to digest complex polymers such as lignocellulose.

Tetramethylammonium hydroxide (TMAH) thermochemolysis for probing in situ softwood lignin modification in each gut segment of the termite

Termites are highly effective in lignocellulose degradation; however, the process of lignin deconstruction along the alimentary canal is not well understood. In this study, the wood metabolites in each gut segment were tentatively analyzed using pyrolysis-gas chromatography-mass spectrometry in the presence of tetramethylammonium hydroxide. Collectively, the significant differences in the pyrolysate distribution among each sample established (1) conservation of the major β-O-4' bonds of lignin during termite digestion, although a selective lignin substructure modification was observed across the whole gut; (2) initiation of lignin-polysaccharide dissociation, aliphatic oxidation/carboxylation, phenolic dehydroxylation in the foregut, and linkage modification of the 5-5', β-5', and β-1' substructures; (3) the continuation of foregut reactions into the midgut with further phenolic carboxylation/demethoxylation/carbonylation; and (4) phenolic/aliphatic esterifications in the hindgut. Overall, elucidation of the stepwise lignin unlocking mechanism in termites provides a valuable insight for understanding plant cell wall structure and its recalcitrance.

Extracellular Ligninolytic Enzymes in Bjerkandera adusta and Lentinus squarrosulus

Extracellular ligninolytic enzyme activities were determined in two white-rot fungi, Bjerkandera adusta and Lentinus squarrosulus. To investigate the activity of extracellular enzymes, cultures were incubated over a period of 20 days in nutrient rich medium (NRM) and nutrient poor medium under static and shaking conditions. Enzymatic activity was varied with media and their incubation conditions. The highest level of Aryl alcohol oxidase (AAO) was detected under shaking condition of both medium while Manganese peroxidase (MnP) activity was best in NRM under both conditions. AAO is the main oxidases enzyme in B. adusta while laccase plays important role in L. squarrosulus. MnP is the main peroxidase enzyme in both varieties.

Characterization of purified and xerogel immobilized novel lignin peroxidase produced from Trametes versicolor IBL-04 using solid state medium of corncobs

BACKGROUND

Cost-effective production of industrially important enzymes is a key for their successful exploitation on industrial scale. Keeping in view the extensive industrial applications of lignin peroxidase (LiP), this study was performed to purify and characterize the LiP from an indigenous strain of Trametes versicolor IBL-04. Xerogel matrix enzyme immobilization technique was applied to improve the kinetic and thermo-stability characteristics of LiP to fulfil the requirements of the modern enzyme consumer sector of biotechnology.

RESULTS

A novel LiP was isolated from an indigenous T. versicolor IBL-04 strain. T. versicolor IBL-04 was cultured in solid state fermentation (SSF) medium of corn cobs and maximum LiP activity of 592 ± 6 U/mL was recorded after five days of incubation under optimum culture conditions. The crude LiP was 3.3-fold purified with specific activity of 553 U/mg after passing through the DEAE-cellulose and Sephadex-G-100 chromatography columns. The purified LiP exhibited a relatively low molecular weight (30 kDa) homogenous single band on native and SDS-PAGE. The LiP was immobilized by entrapping in xerogel matrix of trimethoxysilane (TMOS) and proplytetramethoxysilane (PTMS) and maximum immobilization efficiency of 88.6% was achieved. The free and immobilized LiPs were characterized and the results showed that the free and immobilized LiPs had optimum pH 6 and 5 while optimum temperatures were 60°C and 80°C, respectively. Immobilization was found to enhance the activity and thermo-stability potential of LiP significantly and immobilized LiP remained stable over broad pH and temperature range as compare to free enzyme. Kinetic constants K(m) and V(max) were 70 and 56 μM and 588 and 417 U/mg for the free and immobilized LiPs, respectively. Activity of this novel extra thermo-stable LiP was stimulated to variable extents by Cu(2+), Mn(2+) and Fe(2+) whereas, Cystein, EDTA and Ag(+) showed inhibitory effects.

CONCLUSIONS

The indigenously isolated white rot fungal strain T. versicolor IBL-04 showed tremendous potential for LiP synthesis in SSF of corncobs in high titters (592 U/mL) than other reported Trametes (Coriolus, Polyporus) species. The results obtained after dual phase characterization suggested xerogel matrix entrapment a promising tool for enzyme immobilization, hyper-activation and stabilization against high temperature and inactivating agents. The pH and temperature optima, extra thermo-stability features and kinetic characteristics of this novel LiP of T. versicolor IBL-04 make it a versatile enzyme for various industrial and biotechnological applications.

Decolorization of Textile Dyes and Degradation of Mono-Azo Dye Amaranth by Acinetobacter calcoaceticus NCIM 2890

Acinetobacter calcoaceticus NCIM 2890 (A. caloaceticus) was found to decolorize 20 different textile dyes of various classes. Decolorization of an azo dye amaranth was observed effectively (91%) at static anoxic condition, whereas agitated culture grew well but showed less decolorization (68%) within 48 h of incubation. Induction of intracellular and extracellular lignin peroxidase, intracellular laccase, dichlorophenol indophenol (DCIP) reductase and riboflavin reductase represented their involvement in the biodegradation of amaranth. The products obtained after degradation of Amaranth were characterized as naphthalene sulfamide, hydroxyl naphthalene diazonium and naphthalene diazonium. The germination and growth of Sorghum vulgare and Phaseolus mungo seeds, and the growth of E. coli and Bacillus substilis were not inhibited by the metabolic products of the dye.

Influence of organic and inorganic compounds on oxidoreductive decolorization of sulfonated azo dye C.I. Reactive Orange 16

An isolated bacterial strain is placed in the branch of the Bacillus genus on the basis of 16S rRNA sequence and biochemical characteristics. It decolorized an individual and mixture of dyes, including reactive, disperse and direct. Bacillus sp. ADR showed 88% decolorization of sulfonated azo dye C.I. Reactive Orange 16 (100 mg L(-1)) with 2.62 mg of dye decolorized g(-1) dry cells h(-1) as specific decolorization rate along with 50% reduction in COD under static condition. The optimum pH and temperature for the decolorization was 7-8 and 30-40 degrees C, respectively. It was found to tolerate the sulfonated azo dye concentration up to 1.0 g L(-1). Significant induction in the activity of an extracellular phenol oxidase and NADH-DCIP reductase enzymes during decolorization of C.I. Reactive Orange 16 suggest their involvement in the decolorization. The metal salt (CaCl2), stabilizers (3,4-dimethoxy benzyl alcohol and o-tolidine) and electron donors (sodium acetate, sodium formate, sodium succinate, sodium citrate and sodium pyruvate) enhanced the C.I. Reactive Orange 16 decolorization rate of Bacillus sp. ADR. The 6-nitroso naphthol and dihydroperoxy benzene were final products obtained after decolorization of C.I. Reactive Orange 16 as characterized using FTIR and GC-MS.

Selection of Trichoderma strains capable of increasing laccase production by Pleurotus ostreatus and Agaricus bisporus in dual cultures

AIMS

To select Trichoderma strains for enhanced laccase production in Pleurotus ostreatus or Agaricus bisporus cultures.

METHODS AND RESULTS

Laccase production by P. ostreatus and A. bisporus was evaluated in liquid (axenic) and solid (dual cultures) malt extract medium. Oxidation of ABTS, DMP and syringaldazine was evaluated in order to assess the potential of Trichoderma strains to enhance laccase production by basidiomycetes. Selected Pleurotus-Trichoderma interactions yielded higher increases in laccase volumetric activity and an additional laccase isoform was produced. By contrast, Agaricus-Trichoderma interactions lead to smaller increases on laccase volumetric activity, probably as result of repression (or degradation) towards one of the laccases isoforms.

CONCLUSIONS

The strains of P. ostreatus and A. bisporus assessed in this work showed good potential as laccase producers. The Trichoderma-mediated biological stimulation of laccase production by P. ostreatus and A. bisporus is relevant in order to develop highly productive processes.

SIGNIFICANCE AND IMPACT OF THE STUDY

Extracellular laccases from basidiomycetes are produced only in small amounts. It is therefore important to increase process productivity for potential industrial applications. The results from this study enable the selection Trichoderma strains capable of increasing laccase production by P. ostreatus or A. bisporus in dual cultures.

Biodegradation of γ-hexachlorocyclohexane (Lindane) by a non-white rot fungus conidiobolus 03-1-56 isolated from litter

Biodegradation of chlorinated pesticide γ-hexachlorocyclohexane (lindane) by a nonwhite rot fungus Conidiobolus 03-1-56 is reported for the first time. Conidiobolus 03-1-56, a phycomyceteous fungus isolated from litter, completely degraded lindane on the 5th day of incubation in the culture medium, and GC-ECD studies confirmed that lindane removal did not occur via adsorption on the fungal biomass. Degradation studies using different medium compositions showed that nitrogen/carbon limiting conditions (stress conditions) and presence of veratryl alcohol, induced the secretion of extracellular oxidative enzymes, which enhanced the rate of lindance biodegradation. Under optimum nutrient-limiting conditions, GC-ECD and GC-MS analysis showed complete absence of any degradation metabolite, indicating that lindane was completely mineralized. Assays for tannic acid utilization and lignin peroxidase showed similar enzymatic profiles between Conidiobolus 03-1-56 and standard white rot fungi Pleurotus ostreatus 1200 and Trametes versicolor 1086. Although Conidiobolus 03-1-56 showed a reduced enzyme activity compared to white rot fungi, preliminary evidence indicates that enzymes responsible for lignin degradation by white rots play a key role in lindane degradation by Conidiobolus 03-1-56.

Enzymatic membrane reactors for biodegradation of recalcitrant compounds. Application to dye decolourisation

Membrane bioreactors are being increasingly used in enzymatic catalysed transformations. However, the application of enzymatic-based treatment systems in the environmental field is rather unusual. The aim of this paper is to overview the application of enzymatic membrane reactors to wastewater treatment, more specifically to dye decolourisation. Firstly, the basic aspects such as different configurations of enzymatic reactors, advantages and disadvantages associated to their utilisation are revised as well as the application of this technology to wastewater treatment. Secondly, dye decolourisation by white-rot fungi and their oxidative enzymes are discussed, presenting an overall view from for in vivo and in vitro systems. Finally, dye decolourisation by manganese peroxidase in an enzymatic membrane reactor in continuous operation is presented.

Effects of various media and supplements on laccase production by some white rot fungi

White rot fungi produce three main extracellular enzymes involved in ligninolysis; laccase, lignin peroxidase and manganese peroxidase. Though all white rot fungi do not produce all three enzymes, laccase occupies an important place in ligninolysis. The present paper reports its production by some white rot fungi; Daedalea flavida, Phlebia brevispora, Phlebia radiata and Polyporus sanguineus under different nutritional conditions. Of the various basal media tested, mineral salts malt extract broth proved to be the best medium for laccase production. Sugarcane bagasse proved to be the best laccase inducer among the various supplements added to different media.

Can dietary intake influence plasma levels of amino acids in liver cirrhosis?

BACKGROUND

Modifications in plasma amino acid patterns in cirrhotics are attributed to impaired liver function, being more evident in alcoholic than in viral cirrhosis.

AIM

To evaluate whether diet influences plasma amino acid concentrations in different aetiological groups of cirrhotics.

PATIENTS

Study population comprised 40 patients with cirrhosis (25 virus- and 15 alcohol-related], all Child A, and 30 healthy subjects (controls).

METHOD

A food frequency and quality questionnaire was utilized to determine dietary history and alcohol intake. Nutritional status was evaluated by anthropometric method. Amino acids were determined, on venous blood samples, using a specific analyzer while cysteine was evaluated by fluorescent high power liquid chromatography

RESULTS

The total daily intake of calories, proteins, lipids, and carbohydrates was similar in all individuals. Food quality distinguished the cirrhotics from the controls, but not the different aetiological groups of cirrhotics. Plasma cysteine levels were significantly lower, while aromatic amino acids and methionine were significantly higher, in all cirrhotics (p<0.001 and p<0.01, respectively, versus controls). The decrease in cysteine and the increase in other amino acids were more marked in alcoholics (p<0.01).

CONCLUSIONS

Ethanol intake, but not diet, further enhances the changes in plasma aromatic amino acids, methionine and cysteine induced by impaired liver function in patients with cirrhosis, suggesting a direct interference of alcohol in their metabolism.

Evidence from spin-trapping for a transient radical on tryptophan residue 171 of lignin peroxidase

The heme enzyme lignin peroxidase contains a unique Cbeta-hydroxylated tryptophan residue (Trp171) on the surface of the enzyme. Mutagenetic substitution of Trp171 abolishes completely the veratryl alcohol oxidation activity of the enzyme. This led us to surmise that Trp171 may be involved in electron transfer from natural substrates to the heme cofactor. Here we present evidence for the formation of a transient radical on Trp171 using spin-trapping in combination with peptide mapping. The spin-trap methyl nitroso propane forms a covalent adduct with Trp171 in the presence of hydrogen peroxide which can be detected by its characteristic visible absorbance spectrum. A very similar chromophore can be obtained in a small molecular model system from N-acetyl tryptophanamide, the spin-trap, and a single-electron abstracting system. The precise site the spin-trap is attached to could be identified in a crystal structure of spin-trap/hydrogen peroxide-treated enzyme as the C6 atom of the indole ring of Trp171. These results indicate that Trp171 is redox-active and that it forms an indole radical by transfer of an electron to the heme of compound I and/or II. Apart from cytochrome c peroxidase and DNA photolyase, lignin peroxidase appears to be the third enzyme only which utilizes a tryptophan residue as an integral part of its redox catalysis.

High production of ligninolytic enzymes from white rot fungi in cereal bran liquid medium

White rot fungi from the University of Alberta Mold Herbarium, identified as able to degrade aromatics from a study of PCB metabolism, were examined for production of ligninolytic enzymes. Production of lignin peroxidase, manganese peroxidase, laccase, and veratryl alcohol oxidase were monitored during growth in different media. Good growth but low enzyme production occurred in a glucose - malt extract - yeast extract medium. Media containing 2% cereal bran in 60 mM phosphate buffer supported high levels of laccase production, up to 13 000 U/L in Coriolopsis gallica UAMH 8260 and manganese peroxidase activity up to 1100 U/L in Bjerkandera adusta UAMH 8258. Cereal bran media supported higher laccase production than 2,5-xylidine and higher manganese peroxidase production than a medium containing manganous ion plus veratryl alcohol.Key words: cereal bran, laccase, manganese peroxidase, white rot fungi.

Fungi in lignocellulose breakdown and biopulping

Biological pulping has the potential to improve the quality of pulp, properties of paper and to reduce energy costs and environmental impact relative to traditional pulping operations. It has been suggested that energy savings alone could make the process economically viable. Other benefits include improved burst strength and tear indices of the product and reduced pitch deposition during the production process. The technology has focused on the white rot fungi, which have complex extracellular ligninolytic enzyme systems that can selectively remove or alter lignin and allow cellulose fibers to be obtained. Although still far from completely understood, these enzyme systems are being characterized mechanistically and on a molecular level with primary emphasis on the enzymes lignin peroxidase, manganese peroxidase and laccase. Scale-up to industrial process requirements presents challenges that are difficult to simulate in laboratory or pilot-scale tests. Inoculation, aeration and heat dissipation are key parameters for maintaining fungal activity. It may be possible to monitor and maintain consistent treatments through a program of active wood chip pile management. Overcoming these challenges will determine, in large part, if biopulping becomes a reality.

Biotransformation of (1-phenyl)ethyl hydroperoxide with Aspergillus niger: a model study on enzyme selectivity and on the induction of peroxidase activity

The biocatalytic enantioselective reduction of (1-phenyl)ethyl hydroperoxide (1) by the fungus Aspergillus niger to the corresponding alcohol 2 involves a multi-enzyme biotransformation of the hydroperoxide 1, as revealed by the change in the enantioselectivity as a function of incubation times. This unusual behavior is not exhibited by other fungi and seems to be restricted to A. niger. Furthermore, the peroxidase and other oxidoreductase activities of A. niger depend on the availability of metal ions such as Fe2+, Mn2+ and Zn2+ in the growth medium, since the addition of Fe2+ ions substantially (threefold) increases the enantioselectivity, whereas addition of Mn2+ and Zn2+ ions decreases it. Finally, the cold shock (4 degrees C) significantly enhances the reduction of the hydroperoxide by the microorganism A. niger.

Cloning and characterization of a cDNA encoding a novel extracellular peroxidase from Trametes versicolor

The white rot basidiomycete Trametes versicolor secretes a large number of peroxidases which are believed to be involved in the degradation of polymeric lignin. These peroxidases have been classified previously as lignin peroxidases or manganese peroxidases (MnP). We have isolated a novel extracellular peroxidase-encoding cDNA sequence from T. versicolor CU1, the transcript levels of which are repressed by low concentrations of Mn2+ and induced by nitrogen and carbon but not induced in response to a range of stresses which have been reported to induce MnP expression.

Transformation of industrial dyes by manganese peroxidases from Bjerkandera adusta and Pleurotus eryngii in a manganese-independent reaction

We investigated the transformation of six industrial azo and phthalocyanine dyes by ligninolytic peroxidases from Bjerkandera adusta and other white rot fungi. The dyes were not oxidized or were oxidized very little by Phanerochaete chrysosporium manganese peroxidase (MnP) or by a chemically generated Mn3+-lactate complex. Lignin peroxidase (LiP) from B. adusta also showed low activity with most of the dyes, but the specific activities increased 8- to 100-fold when veratryl alcohol was included in the reaction mixture, reaching levels of 3.9 to 9.6 U/mg. The B. adusta and Pleurotus eryngii MnP isoenzymes are unusual because of their ability to oxidize aromatic compounds like 2,6-dimethoxyphenol and veratryl alcohol in the absence of Mn2+. These MnP isoenzymes also decolorized the azo dyes and the phthalocyanine complexes in an Mn2+-independent manner. The reactions with the dyes were characterized by apparent Km values ranging from 4 to 16 microM and specific activities ranging from 3.2 to 10.9 U/mg. Dye oxidation by these peroxidases was not increased by adding veratryl alcohol as it was in LiP reactions. Moreover, the reaction was inhibited by the presence of Mn2+, which in the case of Reactive Black 5, an azo dye which is not oxidized by the Mn3+-lactate complex, was found to act as a noncompetitive inhibitor of dye oxidation by B. adusta MnP1.

Comparison of gas chromatography and mineralization experiments for measuring loss of selected polychlorinated biphenyl congeners in cultures of white rot fungi

Two methods were used to compare the biodegradation of six polychlorinated biphenyl (PCB) congeners by 12 white rot fungi. Four fungi were found to be more active than Phanerochaete chrysosporium ATCC 24725. Biodegradation of the following congeners was monitored by gas chromatography: 2,3-dichlorobiphenyl, 4,4'-dichlorobiphenyl, 2,4',5-trichlorobiphenyl (2,4',5-TCB), 2,2',4,4'-tetrachlorobiphenyl, 2,2',5,5'-tetrachlorobiphenyl, and 2,2',4,4',5,5'-hexachlorobiphenyl. The congener tested for mineralization was 2,4',5-[U-14C]TCB. Culture supernatants were also assayed for lignin peroxidase and manganese peroxidase activities. Of the fungi tested, two strains of Bjerkandera adusta (UAMH 8258 and UAMH 7308), one strain of Pleurotus ostreatus (UAMH 7964), and Trametes versicolor UAMH 8272 gave the highest biodegradation and mineralization. P. chrysosporium ATCC 24725, a strain frequently used in studies of PCB degradation, gave the lowest mineralization and biodegradation activities of the 12 fungi reported here. Low but detectable levels of lignin peroxidase and manganese peroxidase activity were present in culture supernatants, but no correlation was observed among any combination of PCB congener biodegradation, mineralization, and lignin peroxidase or manganese peroxidase activity. With the exception of P. chrysosporium, congener loss ranged from 40 to 96%; however, these values varied due to nonspecific congener binding to fungal biomass and glassware. Mineralization was much lower, </=11%, because it measures a complete oxidation of at least part of the congener molecule but the results were more consistent and therefore more reliable in assessment of PCB biodegradation.

2-Chloro-1,4-Dimethoxybenzene as a Novel Catalytic Cofactor for Oxidation of Anisyl Alcohol by Lignin Peroxidase

2-Chloro-1,4-dimethoxybenzene (2Cl-14DMB) is a natural compound produced de novo by several white rot fungi. This chloroaromatic metabolite was identified as a cofactor superior to veratryl alcohol (VA) in the oxidation of anisyl alcohol (AA) by lignin peroxidase (LiP). Our results reveal that good LiP substrates, such as VA and tryptophan, are comparatively poor cofactors in the oxidation of AA. Furthermore, we show that a good cofactor does not necessarily serve a role in protecting LiP against H 2 O 2 inactivation. 2Cl-14DMB was not a direct mediator of AA oxidation, since increasing AA concentrations did not inhibit the oxidation of 2Cl-14DMB at all. However, the high molar ratio of anisaldehyde formed to 2Cl-14DMB consumed, up to 13:1, indicates that a mechanism which recycles the cofactor is present.

Regulation of Laccase Gene Transcription in Trametes versicolor

The expression of laccase in the white rot fungus Trametes versicolor is regulated at the level of gene transcription by copper and nitrogen. We used reverse transcription-PCR to demonstrate that as the concentration of copper or nitrogen in fungal cultures was increased, an increase in laccase activity, corresponding to increased laccase gene transcription levels, was observed. In addition, we demonstrated that the amounts of laccase mRNA and laccase activity in 10-day-old cultures were a direct function of the concentration of either 1-hydroxybenzotriazole, a previously described laccase substrate, or 2,5-xylidine, a well-known laccase inducer, in the medium. No induction was observed after the addition of two aromatic acids, ferulic acid and veratric acid, which have been shown to induce laccase production in other white rot fungi. When either copper, 2,5-xylidine, or both compounds were added to cultures grown in the absence of copper, increased laccase transcript levels were detected within 15 min. Corresponding increases in laccase activity were observed after 24-h incubation only when copper was present.