Oxidative degradation of high molecular weight chlorolignin by manganese peroxidase of Phanerochaete chrysosporium

Bioremoval of humic acid from water by white rot fungi: exploring the removal mechanisms

Twelve white rot fungi (WRF) strains were screened on agar plates for their ability to bleach humic acid (HA). Four fungal strains were selected and tested in liquid media for removal of HA. Bioremediation was investigated by HA color removal and changes in the concentration and molecular size distribution of HA by size exclusion chromatography. Trametes versicolor and Phanerochaete chrysosporium showed the highest HA removal efficiency, reaching about 80%. Laccase and manganese peroxidase were measured as extracellular enzymes and their relation to the HA removal by WRF was investigated. Results indicated that nitrogen limitation could enhance the WRF extracellular enzyme activity, but did not necessarily increase the HA removal by WRF. The mechanism of bioremediation by WRF was shown to involve biosorption of HA by fungal biomass and degradation of HA to smaller molecules. Also, contradicting previous reports, it was shown that the decolorization of HA by WRF could not necessarily be interpreted as degradation of HA. Biosorption experiments revealed that HA removal by fungal biomass is dependent not only on the amount of biomass as the sorbent, but also on the fungal species. The involvement of cytochrome P450 (CYP) enzymes was confirmed by comparing the HA removal capability of fungi with and without the presence of a CYP inhibitor. The ability of purified laccase from WRF to solely degrade HA was proven and the importance of mediators was also demonstrated.

Vault Nanoparticles Packaged with Enzymes as an Efficient Pollutant Biodegradation Technology

Vault nanoparticles packaged with enzymes were synthesized as agents for efficiently degrading environmental contaminants. Enzymatic biodegradation is an attractive technology for in situ cleanup of contaminated environments because enzyme-catalyzed reactions are not constrained by nutrient requirements for microbial growth and often have higher biodegradation rates. However, the limited stability of extracellular enzymes remains a major challenge for practical applications. Encapsulation is a recognized method to enhance enzymatic stability, but it can increase substrate diffusion resistance, lower catalytic rates, and increase the apparent half-saturation constants. Here, we report an effective approach for boosting enzymatic stability by single-step packaging into vault nanoparticles. With hollow core structures, assembled vault nanoparticles can simultaneously contain multiple enzymes. Manganese peroxidase (MnP), which is widely used in biodegradation of organic contaminants, was chosen as a model enzyme in the present study. MnP was incorporated into vaults via fusion to a packaging domain called INT, which strongly interacts with vaults' interior surface. MnP fused to INT and vaults packaged with the MnP-INT fusion protein maintained peroxidase activity. Furthermore, MnP-INT packaged in vaults displayed stability significantly higher than that of free MnP-INT, with slightly increased Km value. Additionally, vault-packaged MnP-INT exhibited 3 times higher phenol biodegradation in 24 h than did unpackaged MnP-INT. These results indicate that the packaging of MnP enzymes in vault nanoparticles extends their stability without compromising catalytic activity. This research will serve as the foundation for the development of efficient and sustainable vault-based bioremediation approaches for removing multiple contaminants from drinking water and groundwater.

Depolymerization of lignosulfonates by submerged cultures of the basidiomycete Irpex consors and cloning of a putative versatile peroxidase

Lignosulfonates are abundantly available byproducts of the paper and pulping industry, and they therefore represent a promising feedstock for new sustainable processes. For industrial applications of lignosulfonates, their molecular weight distribution is a critical factor. In order to decrease the average molecular weight of lignosulfonates, Seventeen basidiomycetes were screened for their capability to depolymerize lignosulfonates from spent sulfite liquor (SSL) in surface and liquid cultures. Five basidiomycetes polymerized the lignosulfonates under the selected conditions. Only Irpex consors was found to efficiently degrade calcium lignosulfonates when SSL (0.5%, w/w) was used as the sole carbon and nitrogen source. The average molecular weight of the lignosulfonates was reduced from ∼26 to ∼4 kDa as determined by size exclusion chromatography (SEC) within two weeks. Various extracellular enzyme activities of I. consors were determined over the culture period. High peroxidase activities were correlating with a high degradation rate and the culture was harvested at the day of highest peroxidase activity. A putative versatile peroxidase was isolated by fast protein liquid chromatography (FPLC) and its encoding cDNA was cloned.

Bleaching of Hardwood Kraft Pulp with Manganese Peroxidase from Phanerochaete sordida YK-624 without Addition of MnSO(inf4)

In vitro bleaching of an unbleached hardwood kraft pulp was performed with partially purified manganese peroxidase (MnP) from the fungus Phanerochaete sordida YK-624 without the addition of MnSO(inf4) in the presence of oxalate, malonate, or gluconate as manganese chelator. When the pulp was treated without the addition of MnSO(inf4), the pulp brightness increased by about 10 points in the presence of 2 mM oxalate, but the brightness did not significantly increase in the presence of 50 mM malonate, a good manganese chelator. Residual MnP activity decreased faster during the bleaching with MnP without MnSO(inf4) in the presence of malonate than in the presence of oxalate. Oxalate reduced MnO(inf2) which already existed in the pulp or was produced from Mn(sup2+) by oxidation with MnP and thus supplied Mn(sup2+) to the MnP system. The presence of gluconate, produced by the H(inf2)O(inf2)-generating enzyme glucose oxidase, also improved the pulp brightness without the addition of MnSO(inf4), although treatment with gluconate was inferior to that with oxalate with regard to increase of brightness. It can be concluded that bleaching of hardwood kraft pulp with MnP, using manganese originally existing in the pulp, is possible in the presence of oxalate, a good manganese chelator and reducing reagent.

In vitro bleaching of hardwood kraft pulp by extracellular enzymes excreted from white rot fungi in a cultivation system using a membrane filter

To clarify the role of excreted extracellular enzymes during long-term incubation in a pulp biobleaching system with white rot fungi, we developed a cultivation system in which a membrane filter is used; this membrane filter can prevent direct contact between hyphae and kraft pulp, but allows extracellular enzymes to attack the kraft pulp. Phanerochaete sordida YK-624 brightened the pulp 21.4 points to 54.0% brightness after a 5-day in vitro treatment; this value was significantly higher than the values obtained with Phanerochaete chrysosporium and Coriolus versicolor after a 7-day treatment. Our results indicate that cell-free, membrane-filtered components from the in vitro bleaching system are capable of delignifying unbleached kraft pulp. Obvious candidates for filterable reagents capable of delignifying and bleaching kraft pulp are peroxidase and phenoloxidase proteins. The level of secreted manganese peroxidase activity in the filterable components was substantial during strain YK-624 in vitro bleaching. A positive correlation between the level of manganese peroxidase and brightening of the pulp was observed.

Biological treatment of the effluent from a bleached kraft pulp mill using basidiomycete and zygomycete fungi

Three white-rot fungi (Pleurotus sajor caju, Trametes versicolor and Phanerochaete chrysosporium) and one soft-rot fungi (Rhizopus oryzae) species confirmed their potential for future applications in the biological treatment of effluents derived from the secondary treatment of a bleached kraft pulp mill processing Eucalyptus globulus. Among the four species P. sajor caju and R. oryzae were the most effective in the biodegradation of organic compounds present in the effluent, being responsible for the reduction of relative absorbance (25-46% at 250 nm and 72-74% at 465 nm) and of chemical oxygen demand levels (74 to 81%) after 10 days of incubation. Laccase (Lac), lignin (Lip) and manganese peroxidases (MnP) expression varied among fungal species, where Lac and LiP activities were correlated with the degradation of organic compounds in the effluent treated with P. sajor caju. The first two axes of a principal component analysis explained 88.9% of the total variation among sub-samples treated with the four fungus species, after different incubation periods. All the variables measured contributed positively to the first component except for the MnP enzyme activity which was the only variable contributing negatively to the first component. Absorbances at 465 nm, LiP and Lac enzyme activities were the variables with more weight on the second component. P. sajor caju revealed to be the only species able to perform the biological treatment without promoting an increment in the toxicity of the effluent to the Vibrio fischeri, as it was assessed by the Microtox assay. The opposite was recorded for the treatments with the other three species of fungus. EC(50-5 min) values ranging between 28 and 57% (effluent concentrations) were recorded even after 10 to 13 days of treatment with P. chrysosporium, R. oryzae or with T. versicolor.

Mechanisms Prevalent during Bioremediation of Wastewaters from the Pulp and Paper Industry

Bioremediation of wastewaters represents an important treatment methodology, especially when examined against the backdrop of ever-stricter legislation that is evolving in order to regulate effluent release into the environment. It has been reported that bioremediation specifically holds promise in solving environmental problems. Crucial questions surrounding the treatment of effluents include: efficiency of the process, economic feasibility, legal requirements, and the mechanisms involved in the remediation process. Of all these issues mentioned, the last requires special attention. This paper investigates these matters and focuses on techniques that are currently employed to determine the efficiency of bioremediation and mechanisms involved therein. The physiological significance of biosorption is also examined, as this subject has not been fully addressed in previous publications.

Biological Bleaching of Chemical Pulps

Use of biotechnology in pulp bleaching has attracted considerable attention and achieved interesting results in recent years. Enzymes of the hemicellulolytic type, particularly xylan-attacking enzymes, xylanases are now used commercially in the mills for pulp treatment and subsequent incorporation into bleach sequences. The aims of the enzymatic treatment depend on the actual mill conditions and may be related to environmental demands, reduction of chemical costs or maintenance or even improvement of product quality. The use of oxidative enzymes from white-rot fungi, that can directly attack lignin, is a second-generation approach, which could produce larger chemical savings than xylanase but has not yet been developed to the full scale. It is being studied in several laboratories in Canada, Japan, the U.S.A. and Europe. Certain white-rot fungi can delignify kraft pulps increasing their brightness and their responsiveness to brightening with chemicals. The fungal treatments are too slow but the enzyme manganese peroxidase and laccase can also delignify pulps and enzymatic processes are likely to be easier to optimize and apply than the fungal treatments. Development work on laccase and manganese peroxidase continues. This article presents an overview of developments in the application of hemicellulase enzymes, lignin-oxidizing enzymes and white-rot fungi in bleaching of chemical pulps. The basic enzymology involved and the present knowledge of the mechanisms of the action of enzymes as well as the practical results and advantages obtained on the laboratory and industrial scale are discussed.

Manganese peroxidase-catalyzed oxidative degradation of vanillylacetone

When 4-(4-hydroxy-3-methoxy-phenyl)-2-butanone (vanillylacetone) was tested for manganese peroxidase (MnP)-catalyzed oxidation, it was found to be degraded with the cleavage of an aromatic ring. Among numerous products of vanillylacetone oxidation, four major ones were purified by thin-layer chromatography and identified using mass spectroscopy (MS) and nuclear magnetic resonance (NMR) analysis. Three of them maintained the aromatic ring structure and were identified as 4-[6,2'-dihydroxy-5,3'-dimethoxy-5'-(3-oxo-butyl)-biphenyl]-butan-2-one, 4-(4-hydroxy-3-methoxyphenyl)-3-buten-2-one, and 4-[6,2'-dihydroxy-5,3'-dimethoxy-5'-(3-oxo-butyl)-biphenyl]-3-buten-2-one. Even though the fourth product could not be purified to a single compound, data from infrared spectroscopy showed that it did not have a benzene ring. From MS and NMR analysis, 3-(3-oxo-butyl)-hexa-2,4-dienedioic acid-1-methyl ester was tentatively suggested as the dominant species. The reaction mechanism was suggested on the basis of the structural information of these products. To our knowledge, this paper is the first report on aromatic ring cleavage of the phenolic compound by MnP.

Conversion of milled pine wood by manganese peroxidase from Phlebia radiata

Purified manganese peroxidase (MnP) from the white-rot basidiomycete Phlebia radiata was found to convert in vitro milled pine wood (MPW) suspended in an aqueous reaction solution containing Tween 20, Mn(2+), Mn-chelating organic acid (malonate), and a hydrogen peroxide-generating system (glucose-glucose oxidase). The enzymatic attack resulted in the polymerization of lower-molecular-mass, soluble wood components and in the partial depolymerization of the insoluble bulk of pine wood, as demonstrated by high-performance size exclusion chromatography (HPSEC). The surfactant Tween 80 containing unsaturated fatty acid residues promoted the disintegration of bulk MPW. HPSEC showed that the depolymerization yielded preferentially lignocellulose fragments with a predominant molecular mass of ca. 0.5 kDa. MnP from P. radiata (MnP3) turned out to be a stable enzyme remaining active for 2 days even at 37 degrees C with vigorous stirring, and 65 and 35% of the activity applied was retained in Tween 20 and Tween 80 reaction mixtures, respectively. In the course of reactions, major part of the Mn-chelator malonate was decomposed (85 to 87%), resulting in an increase of pH from 4.4 to >6.5. An aromatic nonphenolic lignin structure (beta-O-4 dimer), which is normally not attacked by MnP, was oxidizible in the presence of pine wood meal. This finding indicates that certain wood components may promote the degradative activities of MnP in a way similar to that promoted by Tween 80, unsaturated fatty acids, or thiols.

Is cellobiose dehydrogenase from Phanerochaete chrysosporium a lignin degrading enzyme?

Cellobiose dehydrogenase (CDH) is an extracellular redox enzyme of ping-pong type, i.e. it has separate oxidative and reductive half reactions. Several wood degrading fungi produce CDH, but the biological function of the enzyme is not known with certainty. It can, however, indirectly generate hydroxyl radicals by reducing Fe(3+) to Fe(2+) and O2 to H2O2. Hydroxyl radicals are then generated by a Fenton type reaction and they can react with various wood compounds, including lignin. In this work we study the effect of CDH on a non-phenolic lignin model compound (3,4-dimethoxyphenyl glycol). The results indicate that CDH can affect lignins in three important ways. (1) It breaks beta-ethers; (2) it demethoxylates aromatic structures in lignins; (3) it introduces hydroxyl groups in non-phenolic lignins. The gamma-irradiated model compound gave a similar pattern of products as the CDH treated model compound, when the samples were analyzed by HPLC, suggesting that hydroxyl radicals are the active component of the CDH system.

Production of manganese peroxidase and organic acids and mineralization of 14C-labelled lignin (14C-DHP) during solid-state fermentation of wheat straw with the white rot fungus nematoloma frowardii

The basidiomycetous fungus Nematoloma frowardii produced manganese peroxidase (MnP) as the predominant ligninolytic enzyme during solid-state fermentation (SSF) of wheat straw. The purified enzyme had a molecular mass of 50 kDa and an isoelectric point of 3.2. In addition to MnP, low levels of laccase and lignin peroxidase were detected. Synthetic 14C-ring-labelled lignin (14C-DHP) was efficiently degraded during SSF. Approximately 75% of the initial radioactivity was released as 14CO2, while only 6% was associated with the residual straw material, including the well-developed fungal biomass. On the basis of this finding we concluded that at least partial extracellular mineralization of lignin may have occurred. This conclusion was supported by the fact that we detected high levels of organic acids in the fermented straw (the maximum concentrations in the water phases of the straw cultures were 45 mM malate, 3.5 mM fumarate, and 10 mM oxalate), which rendered MnP effective and therefore made partial direct mineralization of lignin possible. Experiments performed in a cell-free system, which simulated the conditions in the straw cultures, revealed that MnP in fact converted part of the 14C-DHP to 14CO2 (which accounted for up to 8% of the initial radioactivity added) and 14C-labelled water-soluble products (which accounted for 43% of the initial radioactivity) in the presence of natural levels of organic acids (30 mM malate, 5 mM fumarate).

Decolorization and detoxification of extraction-stage effluent from chlorine bleaching of kraft pulp by Rhizopus oryzae

Rhizopus oryzae, a zygomycete, was found to decolorize, dechlorinate, and detoxify bleach plant effluent at lower cosubstrate concentrations than the basidiomycetes previously investigated. With glucose at 1 g/liter, this fungus removed 92 to 95% of the color, 50% of the chemical oxygen demand, 72% of the adsorbable organic halide, and 37% of the extractable organic halide in 24 h at temperatures of 25 to 45 degrees C and a pH of 3 to 5. Even without added cosubstrate the fungus removed up to 78% of the color. Monomeric chlorinated aromatic compounds were removed almost completely, and toxicity to zebra fish was eliminated. The fungal mycelium could be immobilized in polyurethane foam and used repeatedly to treat batches of effluent. The residue after treatment was not further improved by exposure to fresh R. oryzae mycelium.

Enzymatic Combustion of Aromatic and Aliphatic Compounds by Manganese Peroxidase from Nematoloma frowardii

The direct involvement of manganese peroxidase (MnP) in the mineralization of natural and xenobiotic compounds was evaluated. A broad spectrum of aromatic substances were partially mineralized by the MnP system of the white rot fungus Nematoloma frowardii . The cell-free MnP system partially converted several aromatic compounds, including [U- 14 C]pentachlorophenol ([U- 14 C]PCP), [U- 14 C]catechol, [U- 14 C]tyrosine, [U- 14 C]tryptophan, [4,5,9,10- 14 C]pyrene, and [ring U- 14 C]2-amino-4,6-dinitrotoluene ([ 14 C]2-AmDNT), to 14 CO 2 . Mineralization was dependent on the ratio of MnP activity to concentration of reduced glutathione (thiol-mediated oxidation), a finding which was demonstrated by using [ 14 C]2-AmDNT as an example. At [ 14 C]2-AmDNT concentrations ranging from 2 to 120 μM, the amount of released 14 CO 2 was directly proportional to the concentration of [ 14 C]2-AmDNT. The formation of highly polar products was also observed with [ 14 C]2-AmDNT and [U- 14 C]PCP; these products were probably low-molecular-weight carboxylic acids. Among the aliphatic compounds tested, glyoxalate was mineralized to the greatest extent. Eighty-six percent of the 14 COOH-glyoxalate and 9% of the 14 CHO-glyoxalate were converted to 14 CO 2 , indicating that decarboxylation reactions may be the final step in MnP-catalyzed mineralization. The extracellular enzymatic combustion catalyzed by MnP could represent an important pathway for the formation of carbon dioxide from recalcitrant xenobiotic compounds and may also have general significance in the overall biodegradation of resistant natural macromolecules, such as lignins and humic substances.

Microorganisms and enzymes involved in the degradation of plant fiber cell walls

One of natures most important biological processes is the degradation of lignocellulosic materials to carbon dioxide, water and humic substances. This implies possibilities to use biotechnology in the pulp and paper industry and consequently, the use of microorganisms and their enzymes to replace or supplement chemical methods is gaining interest. This chapter describes the structure of wood and the main wood components, cellulose, hemicelluloses and lignins. The enzyme and enzyme mechanisms used by fungi and bacteria to modify and degrade these components are described in detail. Techniques for how to assay for these enzyme activities are also described. The possibilities for biotechnology in the pulp and paper industry and other fiber utilizing industries based on these enzymes are discussed.

Developments in biotechnological research in Austria

Austria is a small European country with a small number of universities and biotechnological industries, but with great efforts in the implementation of environmental consciousness and corresponding legal standards. This review attempts to describe the biotechnological landscape of Austria, thereby focusing on the highlights in research by industry, universities, and research laboratories, as published during 1990 to early 1995. These will include microbial metabolite (organic acids, antibiotics) and biopolymer (polyhydroxibutyrate, S-layers) production; enzyme (cellulases, hemicellulases, ligninases) technology and biocatalysis; environmental biotechnology; plant breeding and plant protection; mammalian cell products; fermenter design; and bioprocess engineering.

Biodegradation of lignin

Lignin is an aromatic polymer forming up to 30% of woody plant tissues, providing rigidity and resistance to biological attack. Because it is insoluble, chemically complex, and lacking in hydrolysable linkages, lignin is a difficult substrate for enzymatic depolymerization. Certain fungi, mostly basidiomycetes, are the only organisms able to extensively biodegrade it; white-rot fungi can completely mineralize lignin, whereas brown-rot fungi merely modify lignin while removing the carbohydrates in wood. Several oxidative and reductive extracellular enzymes (lignin peroxidase, manganese peroxidase, laccase, and cellobiose:quinone oxidoreductase) have been isolated from ligninolytic fungi; the role of these enzymes in lignin biodegradation is being intensively studied. Enzymatic combustion, a process wherein enzymes generate reactive intermediates, but do not directly control the reactions leading to lignin breakdown, has been proposed as the mechanism of lignin biodegradation. The economic consequences of lignin biodegradation include wood decay and the biogeochemical cycling of woody biomass. Efforts are being made to harness the delignifying abilities of white-rot fungi to aid wood and straw pulping and pulp bleaching. These fungi can also be used to degrade a variety of pollutants in wastewaters and soils, to increase the digestibility of lignocellulosics, and possibly to bioconvert lignins to higher value products. Key words: delignification, white-rot fungi, biobleaching, lignin peroxidase, manganese peroxidase, laccase.

Production and Characterization of Trametes versicolor Mutants Unable To Bleach Hardwood Kraft Pulp

Protoplasts of the monokaryotic strain 52J of Trametes versicolor were treated with UV light and screened for the inability to produce a colored precipitate on guaiacol-containing agar plates. Mutants unable to oxidize guaiacol had absent or very low secretion of laccase and manganese peroxidase (MnP) proteins. All isolates unable to secrete MnP were also unable to bleach or delignify kraft pulp. One mutant strain, M49, which grew normally but did not oxidize guaiacol, was tested further with a number of other substrates whose degradation has been associated with delignification by white rot fungi. Compared with the parent, 52J, mutant M49, secreting no MnP and low laccase, could not brighten or delignify kraft pulp, produced less ethylene from 2-keto methiolbutyric acid, released much less (sup14)CO(inf2) from [(sup14)C]DHP (a synthetic lignin-like polymerizate), and produced much less methanol from pulp. This mutant also displayed decreased abilities to oxidize the dyes poly B-411, poly R-478, and phenol red compared with the wild-type strain and was also unable to decolorize kraft bleachery effluent or mineralize its organochlorine. Addition of purified MnP in conjunction with H(inf2)O(inf2), MnSO(inf4), and an Mn(III) chelator to M49 cultures partially restored methanol production, pulp delignification, and biobleaching in some cases.

Bleaching of Hardwood Kraft Pulp with Manganese Peroxidase Secreted from Phanerochaete sordida YK-624

In vitro bleaching of an unbleached hardwood kraft pulp was performed with manganese peroxidase (MnP) from the fungus Phanerochaete sordida YK-624. When the kraft pulp was treated with partially purified MnP in the presence of MnSO 4 , Tween 80, and sodium malonate with continuous addition of H 2 O 2 at 37°C for 24 h, the pulp brightness increased by about 10 points and the kappa number decreased by about 6 points compared with untreated pulp. The pulp brightness was also increased by 43 points to 75.5% by multiple (six) treatments with MnP combined with alkaline extraction. Our results indicate that in vitro degradation of residual lignin in hardwood kraft pulp with MnP is possible.

Molecular biology of the lignin-degrading basidiomycete Phanerochaete chrysosporium

The white rot basidiomycete Phanerochaete chrysosporium completely degrades lignin and a variety of aromatic pollutants during the secondary metabolic phase of growth. Two families of secreted heme enzymes, lignin peroxidase (LiP) and manganese peroxidase (MnP), are major components of the extracellular lignin degradative system of this organism. MnP and LiP both are encoded by families of genes, and the lip genes appear to be clustered. The lip genes contain eight or nine short introns; the mnp genes contain six or seven short introns. The sequences surrounding active-site residues are conserved among LiP, MnP, cytochrome c peroxidase, and plant peroxidases. The eight LiP cysteine residues align with 8 of the 10 cysteines in MnP. LiPs are synthesized as preproenzymes with a 21-amino-acid signal sequence followed by a 6- or 7-amino-acid propeptide. MnPs have a 21- or 24-amino-acid signal sequence but apparently lack a propeptide. Both LiP and MnP are regulated at the mRNA level by nitrogen, and the various isozymes may be differentially regulated by carbon and nitrogen. MnP also is regulated at the level of gene transcription by Mn(II), the substrate for the enzyme, and by heat shock. The promoter regions of mnp genes contain multiple heat shock elements as well as sequences that are identical to the consensus metal regulatory elements found in mammalian metallothionein genes. DNA transformation systems have been developed for P. chrysosporium and are being used for studies on gene regulation and for gene replacement experiments.

Effects of Kraft Pulp and Lignin on Trametes versicolor Carbon Metabolism

The white rot basidiomycete Trametes ( Coriolus ) versicolor can substantially increase the brightness and decrease the lignin content of washed, unbleached hardwood kraft pulp (HWKP). Monokaryotic strain 52J was used to study how HWKP and the lignin in HWKP affect the carbon metabolism and secretions of T. versicolor. Earlier work indicated that a biobleaching culture supernatant contained all components necessary for HWKP biobleaching and delignification, but the supernatant needed frequent contact with the fungus to maintain these activities. Thus, labile small fungal metabolites may be the vital biobleaching system components renewed or replaced by the fungus. Nearly all of the CO 2 evolved by HWKP-containing cultures came from the added glucose, indicating that HWKP is not an important source of carbon or energy during biobleaching. Carbon dioxide appeared somewhat earlier in the absence of HWKP, but the culture partial O 2 pressure was little affected by the presence of pulp. The presence of HWKP in a culture markedly increased the culture's production of a number of acidic metabolites, including 2-phenyllactate, oxalate, adipate, glyoxylate, fumarate, mandelate, and glycolate. Although the total concentration of these pulp-induced metabolites was only 4.3 mM, these compounds functioned as effective manganese-complexing agents for the manganese peroxidase-mediated oxidation of phenol red, propelling the reaction at 2.4 times the rate of 50 mM sodium malonate, the standard chelator-buffer. The presence of HWKP in a culture also markedly stimulated fungal secretion of the enzymes manganese peroxidase, cellulase, and cellobiose-quinone oxidoreductase, but not laccase (phenol oxidase) or lignin peroxidase.

Manganese Peroxidase, Produced by Trametes versicolor during Pulp Bleaching, Demethylates and Delignifies Kraft Pulp

Previous work has shown that Trametes ( Coriolus ) versicolor bleaches kraft pulp brownstock with the concomitant release of methanol. In this work, the fungus is shown to produce both laccase and manganese peroxidase (MnP) but not lignin peroxidase during pulp bleaching. MnP production was enhanced by the presence of pulp and/or Mn(II) ions. The maximum level of secreted MnP was coincident with the maximum rate of fungal bleaching. Culture filtrates isolated from bleaching cultures produced Mn(II)- and hydrogen peroxide-dependent pulp demethylation and delignification. Laccase and MnP were separated by ion-exchange chromatography. Purified MnP alone produced most of the demethylation and delignification exhibited by the culture filtrates. On the basis of the methanol released and the total and phenolic methoxyl contents of the pulp, it appears that MnP shows a preference for the oxidation of phenolic lignin substructures. The extensive increase in brightness observed in the fungus-treated pulp was not found with MnP alone. Therefore, either the MnP effect must be optimized or other enzymes or compounds from the fungus are also required for brightening.

Mineralization of sulfonated azo dyes and sulfanilic acid by Phanerochaete chrysosporium and Streptomyces chromofuscus

Five 14C-radiolabeled azo dyes and sulfanilic acid were synthesized and used to examine the relationship between dye substitution patterns and biodegradability (mineralization to CO2) by a white-rot fungus and an actinomycete. 4-Amino-[U-14C]benzenesulfonic acid and 4-(3-sulfo-4-aminophenylazo)-[U-14C]benzenesulfonic acid were used as representative compounds having sulfo groups or both sulfo and azo groups. Such compounds are not known to be present in the biosphere as natural products. The introduction of lignin-like fragments into the molecules of 4-amino-[U-14C]benzenesulfonic acid and 4-(3-sulfo-4-aminophenylazo)-[U-14C]benzenesulfonic acid by coupling reactions with guaiacol (2-methoxyphenol) resulted in the formation of the dyes 4-(3-methoxy-4-hydroxyphenylazo)-[U-14C]benzenesulfonic acid and 4-(2-sulfo-3'-methoxy-4'-hydroxy-azobenzene-4-azo)-[U-14C]benzenesulf oni c acid, respectively. The synthesis of acid azo dyes 4-(2-hydroxy-1-naphthylazo)-[U-14C]benzenesulfonic acid and 4-(4-hydroxy-1-naphthylazo)-[U-14C]benzenesulfonic acid also allowed the abilities of these microorganisms to mineralize these commercially important compounds to be evaluated. Phanerochaete chrysosporium mineralized all of the sulfonated azo dyes, and the substitution pattern did not significantly influence the susceptibility of the dyes to degradation. In contrast, Streptomyces chromofuscus was unable to mineralize aromatics with sulfo groups and both sulfo and azo groups. However, it mediated the mineralization of modified dyes containing lignin-like substitution patterns. This work showed that lignocellulolytic fungi and bacteria can be used for the biodegradation of anionic azo dyes, which thus far have been considered among the xenobiotic compounds most resistant to biodegradation.(ABSTRACT TRUNCATED AT 250 WORDS)

Production of manganic chelates by laccase from the lignin-degrading fungus Trametes (Coriolus) versicolor

Many ligninolytic basidiomycete fungi have been shown to secrete a group of peroxidase isozymes whose sole function appears to be the peroxide-dependent oxidation of manganous [Mn(II)] to manganic [Mn(III)] ions. Manganic chelates and these Mn peroxidases have been implicated as central to the degradation of various natural and synthetic lignins and lignin-containing effluents by white rot (ligninolytic) fungi. Another group of enzymes, the laccases, are commonly secreted by wood-rotting fungi, but are generally regarded as being able to oxidize (and usually polymerize) only phenolic substrates. In this report it is shown that in the presence of appropriate oxidizable phenolic accessory substances or primary substrates, a variety of laccases and peroxidases catalyzing one-electron oxidations can also produce Mn(III) chelates from Mn(II).