Immunocytochemical localization of laccase L1 in wood decayed by Rigidoporus lignosus

Biodegradation of bisphenol A using psychrotolerant bacterial strain Pseudomonas palleroniana GBPI_508

A psychrotolerant bacterial strain of Pseudomonas sp. (P. palleroniana GBPI_508), isolated from the Indian Himalayan region, is studied for analyzing its potential for degrading bisphenol A (BPA). Response surface methodology using Box-Behnken design was used to statistically optimize the environmental factors during BPA degradation and the maximum degradation (97%) was obtained at optimum conditions of mineral salt media pH 9, experimental temperature 25 °C, an inoculum volume of 10% (v/v), and agitation speed 130 rpm at the BPA concentration 270 mg L^-1. The Monod model was used for understanding bacterial degradation kinetics, and 37.5 mg^-1 half saturation coefficient (K_S) and 0.989 regression coefficient (R²) were obtained. Besides, the utmost specific growth rate µmax was witnessed as 0.080 h^-1 with the GBPI_508 during BPA degradation. Metabolic intermediates detected in this study by GC-MS were identified as valeric acid, propionic acid, diglycolic acid, and phenol. The psychrotolerant bacterial strain of Pseudomonas sp. (P. palleroniana GBPI_508), isolated from the Indian Himalayan region has shown good potential for remediation of BPA at variable conditions.

Differential regulation by organic compounds and heavy metals of multiple laccase genes in the aquatic hyphomycete Clavariopsis aquatica

To advance the understanding of the molecular mechanisms controlling microbial activities involved in carbon cycling and mitigation of environmental pollution in freshwaters, the influence of heavy metals and natural as well as xenobiotic organic compounds on laccase gene expression was quantified using quantitative real-time PCR (qRT-PCR) in an exclusively aquatic fungus (the aquatic hyphomycete Clavariopsis aquatica) for the first time. Five putative laccase genes (lcc1 to lcc5) identified in C. aquatica were differentially expressed in response to the fungal growth stage and potential laccase inducers, with certain genes being upregulated by, e.g., the lignocellulose breakdown product vanillic acid, the endocrine disruptor technical nonylphenol, manganese, and zinc. lcc4 is inducible by vanillic acid and most likely encodes an extracellular laccase already excreted during the trophophase of the organism, suggesting a function during fungal substrate colonization. Surprisingly, unlike many laccases of terrestrial fungi, none of the C. aquatica laccase genes was found to be upregulated by copper. However, copper strongly increases extracellular laccase activity in C. aquatica, possibly due to stabilization of the copper-containing catalytic center of the enzyme. Copper was found to half-saturate laccase activity already at about 1.8 μM, in favor of a fungal adaptation to low copper concentrations of aquatic habitats.

Characterization of two new multiforms of Trametes pubescens laccase

Electrochemical properties of two multiforms of laccase from Trametes pubescens basidiomycete (LAC1 and LAC2) have been studied. The standard redox potentials of the T1 sites of the enzymes were found to be 746 and 738 mV vs. NHE for LAC1 and LAC2, respectively. Bioelectroreduction of oxygen based on direct electron transfer between each of the two forms of Trametes pubescens laccase and spectrographic graphite electrodes has been demonstrated and studied. It is concluded that the T1 site of laccase is the first electron acceptor, both in solution (homogeneous case) and when the enzymes are adsorbed on the surface of the graphite electrode (heterogeneous case). Thus, the previously proposed mechanism of oxygen bioelectroreduction by adsorbed fungal laccase was additionally confirmed using two forms of the enzyme. Moreover, the assumed need for extracellular laccase to communicate directly and electronically with a solid matrix (lignin) in the course of lignin degradation is discussed. In summary, the possible roles of multiforms of the enzyme based on their electrochemical, biochemical, spectral, and kinetic properties have been suggested to consist in broadening of the substrate specificity of the enzyme, in turn yielding the possibility to dynamically regulate the process of lignin degradation according to the real-time survival needs of the organism.

Estimation of bound and free fractions of lignocellulose-degrading enzymes of wood-rotting fungi Pleurotus ostreatus, Trametes versicolor and Piptoporus betulinus

Liquid cultures with cellulose and solid state fermentation cultures on wheat straw of the white-rot fungi Pleurotus ostreatus and Trametes versicolor and the brown-rot fungus Piptoporus betulinus were assayed for the free and solid fraction-bound activity of lignocellulose-degrading enzymes. The majority of the ligninolytic enzymes laccase and Mn peroxidase was detected in the free fraction of P. ostreatus and T. versicolor. The endocleaving enzymes endo-1,4-beta-glucanase, endo-1,4-beta-mannanase and endo-1,4-beta-xylanase were detected almost exclusively in the free fraction, while significant amounts of 1,4-beta-glucosidase, cellobiohydrolase, 1,4-beta-xylosidase and 1,4-beta-mannosidase were present in the bound fraction depending on the mode of cultivation and the species. The bound enzymes accounted for 66% of the total activity in P. ostreatus straw cultures, 35% in T. versicolor and only 8% in P. betulinus. The enzymes also showed significant differences in freeze-drying stability. Hydrolases in general showed high stability, whereas laccase and Mn peroxidase of P. ostreatus were the least stable.

Fungal laccases – occurrence and properties

Laccases of fungi attract considerable attention due to their possible involvement in the transformation of a wide variety of phenolic compounds including the polymeric lignin and humic substances. So far, more than a 100 enzymes have been purified from fungal cultures and characterized in terms of their biochemical and catalytic properties. Most ligninolytic fungal species produce constitutively at least one laccase isoenzyme and laccases are also dominant among ligninolytic enzymes in the soil environment. The fact that they only require molecular oxygen for catalysis makes them suitable for biotechnological applications for the transformation or immobilization of xenobiotic compounds.

The intercellular biotrophic leaf pathogen Cymadothea trifolii locally degrades pectins, but not cellulose or xyloglucan in cell walls of Trifolium repens

The intercellular ascomycetous pathogen Cymadothea trifolii, causing sooty blotch of clover, proliferates within leaves of Trifolium spp. and produces a complex structure called interaction apparatus (IA) in its own hyphae. Opposite the IA the plant plasmalemma invaginates to form a bubble. Both structures are connected by a tube with an electron-dense sheath. Using immunocytochemistry on high-pressure frozen and freeze-substituted samples, we examined several plant and fungal cell wall components, including those in new host wall appositions at the interaction site, as well as a fungal polygalacturonase. Within the tube linking IA and host bubble, labelling was obtained for cellulose and xyloglucan but not for rhamnogalacturonan-I and homogalacturonans. The IA labelled for chitin and beta-1,3-glucans, and for a fungal polygalacturonase. Plant wall appositions reacted with antibodies against callose, xyloglucans and rhamnogalacturonan-I. Cymadothea trifolii partly degrades the host cell wall. Structural elements remain intact, but the pectin matrix is dissolved. A fungal polygalacturonase detected in the IA is probably a key factor in this process. Owing to the presence of chitin and beta-1,3-glucans, the IA itself is considered an apoplastic compartment.

Structure and expression of a laccase gene from the ligninolytic basidiomycete Ceriporiopsis subvermispora

A gene encoding laccase has been isolated from a genomic library of the white-rot basidiomycete Ceriporiopsis subvermispora constructed in Lambda GEM-11. This gene (Cs-lcs1) contains an open reading frame of 2215 bp, encoding a mature protein of 499 amino acids with a 21-residue signal peptide. The protein sequence exhibits between 63 and 68% identity with laccases from other basidiomycetes and shares with all of them 10 conserved histidines and one cysteine involved in the coordination of copper atoms at the active site of the enzyme. The gene possesses 11 introns, with splicing junctions and internal lariat formation sites adhering to the GT-AG and CTRAY rules, respectively. The upstream region of Cs-lcs1 contains a TATA box, two CAAT sites, five putative metal response elements and a ACE1 element. In agreement with the presence of the latter element, transcription of Cs-lcs1 is activated by copper and silver, as shown by Northern blot and reverse transcription followed by DNA amplification analyses. Based on Southern blot analysis, Cs-lcs1 appears to be the only gene encoding laccase in C. subvermispora.

Electron and fluorescence microscopy of extracellular glucan and aryl-alcohol oxidase during wheat-straw degradation by Pleurotus eryngii

The ligninolytic fungus Pleurotus eryngii grown in liquid medium secreted extracellular polysaccharide (87% glucose) and the H2O2-producing enzyme aryl-alcohol oxidase (AAO). The production of both was stimulated by wheat-straw. Polyclonal antibodies against purified AAO were obtained, and a complex of glucanase and colloidal gold was prepared. With these tools, the localization of AAO and extracellular glucan in mycelium from liquid medium and straw degraded under solid-state fermentation conditions was investigated by transmission electron microscopy (TEM) and fluorescence microscopy. These studies revealed that P. eryngii produces a hyphal sheath consisting of a thin glucan layer. This sheath appeared to be involved in both mycelial adhesion to the straw cell wall during degradation and AAO immobilization on hyphal surfaces, with the latter evidenced by double labelling. AAO distribution during differential degradation of straw tissues was observed by immunofluorescence microscopy. Finally, TEM immunogold studies confirmed that AAO penetrates the plant cell wall during P. eryngii degradation of wheat straw.

Morphogenesis and mechanisms of penetration by plant pathogenic fungi

Infection structures of phytopathogenic fungi are modified hyphae specialized for the invasion of plant tissues. Initial events are adhesion to the cuticle and directed growth of the germ tube on the plant surface. At the site of penetration, appressoria are often formed that may have melanized walls and develop high turgor pressure to support the penetration process. The penetration hypha accumulates components of the cytoskeleton in the tip and secretes a variety of cell wall-degrading enzymes in a highly regulated fashion in order to penetrate the cuticle and the plant cell wall. This article reviews recent papers on the cytology, physiology, and molecular biology of the penetration process.

Synthetic Lignin Mineralization by Ceriporiopsis subvermispora Is Inhibited by an Increase in the pH of the Cultures Resulting from Fungal Growth

(sup14)C-synthetic lignin mineralization by the basidiomycete Ceriporiopsis subvermispora occurs at the highest rate (about 30% after 29 days) in liquid cultures containing 1% glucose and a growth-limiting amount (1 mM) of ammonium tartrate. The titers of manganese peroxidase (MnP) and laccase are lower in these cultures than in cultures containing 1% glucose and 10 mM ammonium tartrate, where the extent of lignin mineralization in the same period is only about 15%. The inverse correlation between enzyme activity and lignin mineralization is also observed when ammonium tartrate is replaced by ammonium chloride or Casamino Acids as the source of nitrogen. This phenomenon can be explained by a gradual increase in the pH of the medium that takes place only in the cultures with high nitrogen concentrations. Supporting this finding, when cultures with 1 mM ammonium tartrate were grown at different pHs, (sup14)CO(inf2) evolved more rapidly from those with pH values near the optimum for MnP activity. On the other hand, (sup14)CO(inf2) evolution from cultures containing 1% glucose supplemented with 1 mM ammonium tartrate plus 9 mM sodium tartrate was as low as that from cultures with a high ammonium tartrate concentration. Since the changes in the pH of these cultures were not as pronounced as those in cultures containing high nitrogen concentrations, tartrate itself may also be contributing to limit the extent of lignin mineralization. Considering that pH instability seems to constitute a common feature of fungal cultures, precautions must be taken to avoid underestimation of their ligninolytic efficiencies.

Cloning and sequencing of a laccase gene from the lignin-degrading basidiomycete Pleurotus ostreatus

The gene (pox1) encoding a phenol oxidase from Pleurotus ostreatus, a lignin-degrading basidiomycete, was cloned and sequenced, and the corresponding pox1 cDNA was also synthesized and sequenced. The isolated gene consists of 2,592 bp, with the coding sequence being interrupted by 19 introns and flanked by an upstream region in which putative CAAT and TATA consensus sequences could be identified at positions -174 and -84, respectively. The isolation of a second cDNA (pox2 cDNA), showing 84% similarity, and of the corresponding truncated genomic clones demonstrated the existence of a multigene family coding for isoforms of laccase in P. ostreatus. PCR amplifications of specific regions on the DNA of isolated monokaryons proved that the two genes are not allelic forms. The POX1 amino acid sequence deduced was compared with those of other known laccases from different fungi.

Wood degradation by Phellinus noxius: ultrastructure and cytochemistry

An ultrastructural and cytochemical investigation of the development of Phellinus noxius, a white-rot fungus, in wood chips of Betula papyrifera was done to gain insight into the cellular mechanisms of wood cell wall degradation. Extracellular sheaths and microhyphae were seen to be involved in wood colonization. Close association was observed between these fungal structures and wood cell walls at both early and advanced stages of wood alteration. Fungal sheaths were often seen deep inside host cell walls, sometimes enclosing residual wood fragments. Investigations using gold probes indicated the occurrence of β-1,3-glucans within the fungal sheaths, while β-1,4-glucans were detected only within the fungal septa. The positive reaction with the PATAg test revealed that polysaccharides such as β-1,6-glucans were important components of the sheath. Chitin, pectin, β-glucosides, galactosamine, mannose, sialic acid, fucose, and fimbrial proteins were not found to be present in the sheath. Our data suggest that extracellular sheaths and microphyphae produced by P. noxius during wood cell wall colonization play an important role in wood degradation.Key words: cellulose, Phellinus, sheath, wood degradation.

A Cytochemical Study of Extracellular Sheaths Associated with Rigidoporus lignosus during Wood Decay

An ultrastructural and cytochemical investigation of the development of Rigidoporus lignosus , a white-rot fungus inoculated into wood blocks, was carried out to gain better insight into the structure and role of the extracellular sheaths produced by this fungus during wood degradation. Fungal sheaths had a dense or loose fibrillar appearance and were differentiated from the fungal cell wall early after wood inoculation. Close association between extracellular fibrils and wood cell walls was observed at both early and advanced stages of wood alteration. Fungal sheaths were often seen deep in host cell walls, sometimes enclosing residual wood fragments. Specific gold probes were used to investigate the chemical nature of R. lignosus sheaths. While labeling of chitin, pectin, β-1,4- and β-1,3-glucans, β-glucosides, galactosamine, mannose, sialic acid, RNA, fucose, and fimbrial proteins over fungal sheaths did not succeed, galactose residues and laccase (a fungal phenoloxidase) were found to be present. The positive reaction of sheaths with the PATAg test indicates that polysaccharides such as β-1,6-glucans are important components. Our data suggest that extracellular sheaths produced by R. lignosus during host cell colonization play an important role in wood degradation. Transportation of lignin-degrading enzymes by extracellular fibrils indicates that alteration of plant polymers may occur within fungal sheaths. It is also proposed that R. lignosus sheaths may be involved in recognition mechanisms in fungal cell-wood surface interactions.