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

Recent Advances in Synthesis and Degradation of Lignin and Lignin Nanoparticles and Their Emerging Applications in Nanotechnology

Lignin is an important commercially produced polymeric material. It is used extensively in both industrial and agricultural activities. Recently, it has drawn much attention from the scientific community. It is abundantly present in nature and has significant application in the production of biodegradable materials. Its wide usage includes drug delivery, polymers and several forms of emerging lignin nanoparticles. The synthesis of lignin nanoparticles is carried out in a controlled manner. The traditional manufacturing techniques are costly and often toxic and hazardous to the environment. This review article highlights simple, safe, climate-friendly and ecological approaches to the synthesis of lignin nanoparticles. The changeable, complex structure and recalcitrant nature of lignin makes it challenging to degrade. Researchers have discovered a small number of microorganisms that have developed enzymatic and non-enzymatic metabolic pathways to use lignin as a carbon source. These microbes show promising potential for the biodegradation of lignin. The degradation pathways of these microbes are also described, which makes the study of biological synthesis much easier. However, surface modification of lignin nanoparticles is something that is yet to be explored. This review elucidates the recent advances in the biodegradation of lignin in the ecological system. It includes the current approaches, methods for modification, new applications and research for the synthesis of lignin and lignin nanoparticles. Additionally, the intricacy of lignin’s structure, along with its chemical nature, is well-described. This article will help increase the understanding of the utilization of lignin as an economical and alternative-resource material. It will also aid in the minimization of solid waste arising from lignin.

Microbial demethylation of lignin: Evidence of enzymes participating in the removal of methyl/methoxyl groups

Lignin is an abundant natural plant aromatic biopolymer containing various functional groups that can be exploited for activating lignin for potential commercial applications. Applications are hindered due to the presence of a high content of methyl/methoxyl groups that affects reactiveness. Various chemical and enzymatic approaches have been investigated to increase the functionality in transforming lignin. Among these is demethylation/demethoxylation, which increases the potential numbers of vicinal hydroxyl groups for applications as phenol-formaldehyde resins. Although the chemical route to lignin demethylation is well-studied, the biological route is still poorly explored. Bacteria and fungi have the ability to demethylate lignin and lignin-related compounds. Considering that appropriate microorganisms possess the biochemical machinery to demethylate lignin by cleaving O-methyl groups liberating methanol, and modify lignin by increasing the vicinal diol content that allows lignin to substitute for phenol in organic polymer syntheses. Certain bacteria through the actions of specific O-demethylases can modify various lignin-related compounds generating vicinal diols and liberating methanol or formaldehyde as end-products. The enzymes include: cytochrome P₄₅₀-aryl-O-demethylase, monooxygenase, veratrate 3-O-demethylase, DDVA O-demethylase (LigX; lignin-related biphenyl 5,5'-dehydrodivanillate (DDVA)), vanillate O-demethylase, syringate O-demethylase, and tetrahydrofolate-dependent-O-demethylase. Although, the fungal counterparts have not been investigated in depth as in bacteria, O-demethylases, nevertheless, have been reported in demethylating various lignin substrates providing evidence of a fungal enzyme system. Few fungi appear to have the ability to secrete O-demethylases. The fungi can mediate lignin demethylation enzymatically (laccase, lignin peroxidase, manganese peroxidase, O-demethylase), or non-enzymatically in brown-rot fungi through the Fenton reaction. This review discusses details on the aspects of microbial (bacterial and fungal) demethylation of lignins and lignin-model compounds and provides evidence of enzymes identified as specific O-demethylases involved in demethylation.

Biobleaching: An eco-friendly approach to reduce chemical consumption and pollutants generation

The pulp and paper industry is known to be a large contributor to environmental pollution due to the huge consumption of chemicals and energy. Several chemicals including H2SO4, Cl2, ClO2, NaOH, and H2O2 are used during the bleaching process. These chemicals react with lignin and carbohydrates to generate a substantial amount of pollutants in bleach effluents. Environmental pressure has compelled the pulp and paper industry to reduce pollutant generation from the bleaching section. Enzymes have emerged as simple, economical, and eco-friendly alternatives for bleaching of pulp. The pretreatment of pulp with enzymes is termed as biobleaching or pre-bleaching. Different microbial enzymes such as xylanases, pectinases, laccases, manganese peroxidases (MnP), and lignin peroxidases are used for biobleaching. Xylanases depolymerize the hemicelluloses precipitated on pulp fiber surfaces and improves the efficiency of bleaching chemicals. Xylanase treatment also increases the pulp fibrillation and reduces the beating time of the pulp. Pectinases hydrolyze pectin available in the pulp fibers and improve the papermaking process. Laccase treatment is found more effective along with mediator molecules (as a laccase-mediator system). Biobleaching of pulp results in the superior quality of pulp along with lower consumption of chlorine-based chemicals and lower generation of adsorbable organic halidesadsorbable organic halides (AOX. An enzyme pretreatment reduces the kappa number of pulp and improves ISO brightness significantly. Better physical strength properties and pulp viscosity have also been observed during biobleaching of pulp.

Vault packaged enzyme mediated degradation of amino-aromatic energetic compounds

Amino-aromatic compounds, 2-amino-4-nitrotoluene (ANT), and 2,4-diaminotoluene (DAT) are carcinogens and environmentally persistent pollutants. In this study, we investigated their degradation by natural manganese peroxidase (nMnP) derived from Phanerochaete chrysosporium and recombinant manganese peroxidase packaged in vaults (vMnP). Encapsulation of manganese peroxidase (MnP) in ribonucleoprotein nanoparticle cages, called vaults, was achieved by creating recombinant vaults in yeast Pichia pastoris. Vault packaging increased the stability of MnP by locally sequestering multiple copies of the enzyme. Within 96  h, both vMnP and nMnP catalyzed over 72% removal of ANT in-vitro, which indicates that vault packaging did not limit substrate diffusion. It was observed that vMnP was more efficient than nMnP and P. chrysosporium for the catalysis of target contaminants. Only 57% of ANT was degraded by P. chrysosporium even when MnP activity reached about 480 U L^-1 in cultures. At 1.5 U L^-1 initial activity, vMnP achieved 38% of ANT and 51% of DAT degradation, whereas even 2.7 times higher activity of nMnP showed insignificant biodegradation of both compounds. These results imply that due to protection by vault cages, vMnP has lower inactivation rates. Thus, it works effectively at lower dosage for a longer duration compared to nMnP without requiring frequent replenishment. Collectively, these results indicate that fungal enzymes packaged in vault nanoparticles are more stable and active, and they would be effective in biodegradation of energetic compounds in industrial processes, waste treatment, and contaminated environments.

Fungal biodegradation of the N-nitrosodimethylamine precursors venlafaxine and O-desmethylvenlafaxine in water

Antidepressant drugs such as Venlafaxine (VFX) and O-desmethylvenlafaxine (ODMVFX) are emerging contaminants that are commonly detected in aquatic environments, since conventional wastewater treatment plants are unable to completely remove them. They can be precursors of hazardous by-products, such as the carcinogenic N-nitrosodimethylamine (NDMA), generated upon water chlorination, as they contain the dimethylamino moiety, necessary for the formation of NDMA. In this study, the capability of three white rot fungi (Trametes versicolor, Ganoderma lucidum and Pleurotus ostreatus) to remove both antidepressants from water and to decrease NDMA formation potential was investigated. Furthermore, transformation by-products (TPs) generated along the treatment process were elucidated and also correlated with their NDMA formation potential. Very promising results were obtained for T. versicolor and G. lucidum, both being able to remove up to 100% of ODMVFX. In the case of VFX, which is very recalcitrant to conventional wastewater treatment, a 70% of removal was achieved by T. versicolor, along with a reduction in NDMA formation potential, thus decreasing the associated problems for human health and the environment. However, the NDMA formation potential remained practically constant during treatment with G. lucidum despite of the equally high VFX removal (70%). This difference was attributed to the generation of different TPs during both fungal treatments. For example, G. lucidum generated more ODMVFX, which actually has a higher NDMA formation potential than the parent compound itself.

Enzyme biotechnology in degradation and modification of plant cell wall polymers

Lignocelluloses are abundant raw materials for production of fuels, chemicals and materials. The purpose of this paper is to review the enzyme-types and enzyme-technologies studied and applied in the processing of the lignocelluloses into different products. The enzymes here are mostly glycoside hydrolases, esterases and different redox enzymes. Enzymatic hydrolysis of lignocellulosic polysaccharides to platform sugars has been widely studied leading to development of advanced commercial products for this purpose. Restricted hydrolysis or oxidation of cellulosic fibers have been applied in processing of pulps to paper products, nanocelluloses and textile fibers. Oxidation, transglycosylation and derivatization have been utilized in functionalization of fibers, cellulosic surfaces and polysaccharides. Enzymatic polymerization, depolymerization and grafting methods are being developed for lignin valorization.

Biobleaching of Acacia kraft pulp with extracellular enzymes secreted by Irpex lacteus KB-1.1 and Lentinus tigrinus LP-7 using low-cost media

The white-rot fungi Irpex lacteus KB-1.1 and Lentinus tigrinus LP-7 have been shown in previous studies to have high biobleaching activity in vivo. The aim of this study was to investigate the activities and stabilities of extracellular enzymes, prepared from I. lacteus and L. tigrinus culture grown in three types of economical media of agricultural and forestry wastes, for biobleaching of Acacia oxygen-delignified kraft pulp using kappa number reduction as an indicator of delignification. After 3 days of incubation, the extracellular enzymes preparations from I. lacteus and L. tigrinus cultures in media of Acacia mangium wood powder supplemented with rice bran and addition 1 % glucose (WRBG), resulted in significant decrease of 4.4 and 6.7 %, respectively. A slightly higher kappa number reduction (7.4 %) was achieved with the combine extracellular enzymes from I. lacteus and L. tigrinus. One of the strategies for reducing the cost of enzyme production for treatment processes in the pulp and paper industry is the utilization of agricultural and forestry waste. Thus, WRBG has potential as a culture medium for producing stable lignolytic enzymes simply and economically.

Molecular characterization of manganese peroxidases from white-rot fungus Polyporus brumalis

The cDNAs of six manganese-dependent peroxidases (MnPs) were isolated from white-rot fungus Polyporus brumalis. The MnP proteins shared similar properties with each other in terms of size (approximately 360-365 amino acids) and primary structure, showing 62-96 % amino acid sequence identity. RT-PCR analysis indicated that these six genes were predominantly expressed in shallow stationary culture (SSC) in a liquid medium. Gene expression was induced by treatment with dibutyl phthalate (DBP) and wood chips. Expression of pbmnp4 was strongly induced by both treatments, whereas that of pbmnp5 was induced only by DBP, while pbmnp6 was induced by wood chips only. Then, we overexpressed pbmnp4 in P. brumalis under the control of the GPD promoter. Overexpression of pbmnp4 effectively increased MnP activity; the transformant that had the highest MnP activity also demonstrated the most effective decolorization of Remazol Brilliant Blue R dye. Identification of MnP cDNAs can contribute to the efficient production of lignin-degradation enzymes and may lead to utilization of basidiomycetous fungi for degradation of lignin and numerous recalcitrant xenobiotics.

Screening of white-rot fungi manganese peroxidases: a comparison between the specific activities of the enzyme from different native producers

In this study manganese peroxidase (MnP) enzymes from selected white-rot fungi were isolated and compared for potential future recombinant production. White-rot fungi were cultivated in small-scale in liquid media and a simplified process was established for the purification of extracellular enzymes.

Five lignin degrading organisms were selected (Bjerkandera sp., Phanerochaete (P.) chrysosporium, Physisporinus (P.) rivulosus, Phlebia (P.) radiata and Phlebia sp. Nf b19) and studied for MnP production in small-scale. Extracellular MnP activity was followed and cultivations were harvested at proximity of the peak activity. The production of MnPs varied in different organisms but was clearly regulated by inducing liquid media components (Mn2+, veratryl alcohol and malonate). In total 8 different MnP isoforms were purified.

Results of this study reinforce the conception that MnPs from distinct organisms differ substantially in their properties. Production of the extracellular enzyme in general did not reach a substantial level. This further suggests that these native producers are not suitable for industrial scale production of the enzyme. The highest specific activities were observed with MnPs from P. chrysosporium (200 U mg-1), Phlebia sp. Nf b19 (55 U mg-1) and P. rivulosus (89 U mg-1) and these MnPs are considered as the most potential candidates for further studies. The molecular weight of the purified MnPs was estimated to be between 45–50 kDa.

Chemical characterization and in vitro fermentation ofBrassicastraw treated with the aerobic fungus,Trametes versicolor

Ramirez-Bribiesca, J. E., Wang, Y., Jin, L., Canam, T., Town, J. R., Tsang, A., Dumonceaux, T. J. and McAllister, T. A. 2011. Chemical characterization and in vitro fermentation of Brassica straw treated with the aerobic fungus, Trametes versicolor . Can. J. Anim. Sci. 91: 695–702. Brassica napus straw (BNS) was either not treated or was treated with two strains of Trametes versicolor; 52J (wild type) or m4D (a cellobiose dehydrogenase-deficient mutant) with four treatments: (i) untreated control (C-BNS), (ii) 52J (B-52J), (iii) m4D (B-m4D) or (iv) m4D+glucose (B-m4Dg). Glucose was provided to encourage growth of the mutant strain. All treatments with T. versicolor decreased (P<0.05) neutral-detergent fibre and increased (P<0.05) protein and the concentration of lignin degradation products in straw. Ergosterol was highest (P<0.05) in straw treated with B-52J, suggesting it generated the most fungal biomass. Insoluble lignin was reduced (P<0.05) in straw treated with B-52J and B-m4D, but not with B-m4Dg. Mannose and xylose concentration were generally higher (P<0.05) in straw treated with fungi, whereas glucose and galactose were lower as compared with C-BNS. The four treatments above were subsequently assessed in rumen in vitro fermentations, along with BNS treated with 2 mL g−1of 5 N NaOH. Concentrations of total volatile fatty acids after 24 and 48h were lower (P<0.05) in incubations that contained BNS treated with T. versicolor as compared with C-BNSor NaOH-treated BNS. Compared with C-BNS, in vitrodry matter disappearance and gas production were increased (P<0.05) by NaOH, but not by treatment with either strain of T. versicolor. Although treatment with T. versicolor did release more lignin degradation products, it did not appear to provide more degradable carbohydrate to in vitro rumen microbial populations, even when a mutant strain with compromised carbohydrate metabolism was utilized. Production of secondary compounds by the aerobic fungi may inhibit rumen microbial fermentation.

Time-resolved selected ion flow tube mass spectrometric quantification of the volatile compounds generated by E. coli JM109 cultured in two different media

Preliminary measurements have been made of the volatile compounds emitted by the bacterium E. coli JM109 cultured in the commonly used media Dulbecco's modified Eagle's medium (DMEM) and lysogeny broth (LB) using selected ion flow tube mass spectrometry, SIFT-MS, as a step towards the real time, non-invasive monitoring of accidental infections of mammalian cell cultures. In one procedure, the culture medium alone and the E. coli cells/medium combination were held at 37 °C in bottles sealed with septa for a given time period, usually overnight, to allow the bacterium to proliferate, after which the captured headspace was analysed directly by SIFT-MS. Several compounds were seen to be produced by the E. coli cells that depended on the liquid medium used: when cultured in DMEM, copious amounts of ethanol, acetaldehyde and hydrogen sulphide were produced; in LB ammonia is the major volatile product. In a second procedure, to ensure aerobic conditions prevailed in the cell culture, selected volatile compounds were monitored by SIFT-MS in real time for several hours above the open-to-air E. coli/DMEM culture held at close to 37 °C. The temporal variations in the concentrations of some compounds, which reflect their production rates in the culture, indicate maxima. Thus, the maxima in the ethanol and acetaldehyde production are a reflection of the reduction of glucose from the DMEM by the vigorous E. coli cells and the maximum in the hydrogen sulphide level is an indication of the loss of the sulphur-bearing amino acids from the DMEM. Serendipitously, emissions from DMEM inadvertently infected with the bacterium C. testosteroni were observed when large quantities of ammonia were seen to be produced. The results of this preliminary study suggest that monitoring volatile compounds might assist in the early detection of bacterial infection in large-scale bioreactors.

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.

Manganese Is Not Required for Biobleaching of Oxygen-Delignified Kraft Pulp by the White Rot Fungus Bjerkandera sp. Strain BOS55

The white rot fungus Bjerkandera sp. strain BOS55 extensively delignified and bleached oxygen-delignified eucalyptus kraft pulp handsheets. Biologically mediated brightness gains of up to 14 ISO (International Standards Organization units) were obtained, providing high final brightness values of up to 80% ISO. In nitrogen-limited cultures (2.2 mM N), manganese (Mn) greatly improved manganese-dependent peroxidase (MnP) production. However, the biobleaching was not affected by the Mn nutrient regimen, ranging from 1,000 (mu)M added Mn to below the detection limit of 0.26 (mu)M Mn in EDTA-extracted pulp medium. The lowest Mn concentration tested was at least several orders of magnitude lower than the K(infm) known for MnP. Consequently, it was concluded that Mn is not required for biobleaching in Bjerkandera sp. strain BOS55. Nonetheless, fast protein liquid chromatography profiles indicated that MnP was the predominant oxidative enzyme produced even under culture conditions in the near absence of manganese. High nitrogen (22 mM N) and exogenous veratryl alcohol (2 mM) repressed biobleaching in Mn-deficient but not in Mn-sufficient culture medium. No correlation was observed between the titers of extracellular peroxidases and the biobleaching. However, the decolorization rate of the polyaromatic dye Poly R-478 was moderately correlated to the biobleaching under a wide range of Mn and N nutrient regimens.

Lignin Peroxidases, Manganese Peroxidases, and Other Ligninolytic Enzymes Produced by Phlebia radiata during Solid-State Fermentation of Wheat Straw

The white rot fungus Phlebia radiata 79 (ATCC 64658) produces lignin peroxidase (LiP), manganese peroxidase (MnP), glyoxal oxidase (GLOX), and laccase in the commonly used glucose low-nitrogen liquid medium. However, the enzymes which this fungus utilizes for selective removal of lignin during degradation of different lignocellulosic substrates have not been studied before. Multiple forms of LiP, MnP, GLOX, and laccase were purified from P. radiata culture extracts obtained after solid-state fermentation of wheat straw. However, the patterns of extracellular lignin-modifying enzymes studied were different from those of the enzymes usually found in liquid cultures of P. radiata. Three LiP isoforms were purified. The major LiP isoform from solid-state cultivation was LiP2. LiP3, which has usually been described as the major isoenzyme in liquid cultures, was not expressed during straw fermentation. New MnP isoforms have been detected in addition to the previously reported MnPs. GLOX was secreted in rather high amounts simultaneously with LiP during the first 2 weeks of growth. GLOX purified from P. radiata showed multiple forms, with pIs ranging from 4.0 to 4.6 and with a molecular mass of ca. 68 kDa.

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.

Pulp bleaching using laccase from Trametes versicolor under high temperature and alkaline conditions

Kraft pulp was delignified using laccase produced by the white rot fungus Trametes versicolor immobilized in solid support under specific conditions. The stability tests showed that this enzyme was stable for 6 h at 55 degrees C and pH 8.0, allowing its use under pH and temperature conditions very close to those used in industrial bleaching. In this work, unbleached hardwood Kraft pulp was submitted to prebleaching using 2 U laccase/g pulp basis. Reaction time, temperature, and pH of the enzymatic treatment were investigated. Good results regarding Kappa number reduction, selectivities, and high viscosities were obtained when prebleaching was performed for 1 h at temperature of 55 degrees C and pH 8.0 followed by alkaline extraction and ECF bleaching sequences.

Screening of Biodegradable Function of Indigenous Ligno-degrading Mushroom Using Dyes

The process of biodegradation in lingo-cellulosic materials is critically relevant to biospheric carbon. The study of this natural process has largely involved laboratory investigations, focused primarily on the biodegradation and recycling of agricultural by-products, generally using basidiomycetes species. In order to collect super white rot fungi and evaluate its ability to degrade lingo-cellulosic material, 35 fungal strains, collected from forests, humus soil, livestock manure, and dead trees, were screened for enzyme activities and their potential to decolorize the commercially used Poly-R 478 dye. In the laccase enzymatic analysis chemical test, 33 white rot fungi and 2 brown rot fungi were identified. The degradation ability of polycyclic aromatic hydrocarbons (PAHs) according to the utilized environmental conditions was higher in the mushrooms grown in dead trees and fallen leaves than in the mushrooms grown in humus soil and livestock manure. Using Poly-R 478 dye to assess the PAH-degradation activity of the identified strains, four strains, including Agrocybe pediades, were selected. The activities of laccase, MnP, and Lip of the four strains with PAH-degrading ability were highest in Pleurotus incarnates. 87 fungal strains, collected from forests, humus soil, livestock manure, and dead trees, were screened for enzyme activities and their potential to decolorize the commercially used Poly-R 478 dye on solid media. Using Poly-R 478 dye to assess the PAHdegrading activity of the identified strains, it was determined that MKACC 51632 and 52492 strains evidenced superior activity in static and shaken liquid cultures. Subsequent screening on plates containing the polymeric dye poly R-478, the decolorization of which is correlated with lignin degradation, resulted in the selection of a strain of Coriolus versicolor, MKACC52492, for further study, primarily due to its rapid growth rate and profound ability to decolorize poly R-478 on solid media. Considering our findings using Poly-R 478 dye to evaluate the PAH-degrading activity of the identified strains, Coriolus versicolor, MKACC 52492 was selected as a favorable strain. Coriolus versicolor, which was collected from Mt. Yeogi in Suwon, was studied for the production of the lignin-modifying enzymes laccase, manganese-dependent peroxidase (MnP), and lignin peroxidase (LiP).

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.

Optimization of laccase production from Trametes versicolor by solid fermentation

The regulation of culture conditions, especially the optimization of substrate constituents, is crucial for laccase production by solid fermentation. To develop an inexpensive optimized substrate formulation to produce high-activity laccase, a uniform design formulation experiment was devised. The solid fermentation of Trametes versicolor was performed with natural aeration, natural substrate pH (about 6.5), environmental humidity of 60% and two different temperature stages (at 37 °C for 3 days, and then at 30 °C for the next 17 days). From the experiment, a regression equation for laccase activity, in the form of a second-degree polynomial model, was constructed using multivariate regression analysis and solved with unconstrained optimization programming. The optimized substrate formulation for laccase production was then calculated. Tween 80 was found to have a negative effect on laccase production in solid fermentation; the optimized solid substrate formulation was 10.8% glucose, 27.7% wheat bran, 9.0% (NH4)2SO4, and 52.5% water. In a scaled-up verification of solid fermentation at a 10 kg scale, laccase activity from T. versicolor in the optimized substrate formulation reached 110.9 IU/g of dry mass.

Bleaching with lignin-oxidizing enzymes

General concern about the environmental impact of chlorine bleaching effluents has led to a trend towards elementary chlorine-free or totally chlorine free bleaching methods. Considerable interest has been focused on the use of biotechnology in pulp bleaching, as large number of microbes and the enzymes produced by them are known to be capable of preferential degradation of native lignin and complete degradation of wood. 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. 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 enzymes produced from the fungi can also delignify pulps and these enzymatic processes are likely to be easier to optimize and apply than the fungal treatments. This article presents an overview of the developments in the application of lignin-oxidizing enzymes in bleaching of chemical pulps. The present knowledge of the mechanisms on the action of enzymes as well as the practical results and advantages obtained on the laboratory and industrial scale are discussed.

Manganese peroxidase from the white-rot fungus Phanerochaete chrysosporium is enzymatically active and accumulates to high levels in transgenic maize seed

Manganese peroxidase (MnP) has been implicated in lignin degradation and thus has potential applications in pulp and paper bleaching, enzymatic remediation and the textile industry. Transgenic plants are an emerging protein expression platform that offer many advantages over traditional systems, in particular their potential for large-scale industrial enzyme production. Several plant expression vectors were created to evaluate the accumulation of MnP from the wood-rot fungus Phanerochaete chrysosporium in maize seed. We showed that cell wall targeting yielded full-length MnP, whereas cytoplasmic localization resulted in multiple truncated peroxidase polypeptides as detected by immunoblot analysis. In addition, the use of a seed-preferred promoter dramatically increased the expression levels and reduced the negative effects on plant health. Multiple independent transgenic lines were backcrossed with elite inbred corn lines for several generations with the maintenance of high-level expression, indicating genetic stability of the transgene.

Molecular cloning of the cDNA encoding laccase from Trametes versicolor and heterologous expression in Pichia methanolica

A cDNA encoding for laccase was isolated from the ligninolytic fungus Trametes versicolor by RNA-PCR. The cDNA corresponds to the gene Lcc1, which encodes a laccase isoenzyme of 498 amino acid residues preceded by a 22-residue signal peptide. The Lcc1 cDNA was cloned into the vectors pMETA and pMETalphaA and expressed in Pichia methanolica. The laccase activity obtained with the Saccharomyces cerevisiae alpha-factor signal peptide was found to be twofold higher than that obtained with the native secretion signal peptide. The extracellular laccase activity in recombinants with the alpha-factor signal peptide was 9.79 U ml(-1). The presence of 0.2 mM copper was necessary for optimal activity of laccase. The expression level was favoured by lower cultivation temperature. The identity of the recombinant protein was further confirmed by immunodetection using Western blot analysis. As expected, the molecular mass of the mature laccase was 64.0 kDa, similar to that of the native form.

Oxidation of polycyclic aromatic hydrocarbons by fungal isolates from an oil contaminated refinery soil

BACKGROUND AND OBJECTIVE

Indigenous soil microorganisms are used for the biodegradation of petroleum hydrocarbons in oily waste residues from the petroleum refining industry. The objective of this investigation was to determine the potential of indigenous strains of fungi in soil contaminated with petroleum hydrocarbons to biodegrade polycyclic aromatic hydrocarbons (PAH).

MATERIALS AND METHODS

Twenty one fungal strains were isolated from a soil used for land-farming of oily waste residues from the petrochemical refining industry in Singapore and identified to genus level using laboratory culture and morphological techniques. Isolates were incubated in the presence of 30 mg/L of phenanthrene over a period of 28 days at 30 degrees C. The most effective strain was further evaluated to determine its ability to oxidise a wider range of PAH compounds of various molecular weight i.e acenaphthene, fluorene, fluoranthene, chrysene, benzo(a)pyrene and dibenz(ah)anthracene

RESULTS AND DISCUSSION

After 28 days of incubation, 18 of the 21 fungal cultures were capable of oxidising over 50% of the phenanthrene present in culture medium, relative to abiotic controls. Fungal isolate, Penicillium sp. 06, was able to oxidise 89% of the phenanthrene present. This isolate could also oxidise more than 75% of the acenaphthene, fluorene and fluoranthene after 30 days of incubation. However, the oxidation of high molecular weight PAH i.e. chrysene, benzo(a)pyrene and dibenz(ah)anthracene by the Penicillium sp. 06 isolate was limited, where the extent of oxidation was inversely proportional to PAH molecular weight.

CONCLUSIONS

Fungal isolate, Penicillium sp. 06, was effective at oxidising a range of PAH in petroleum contaminated soils, but higher molecular weight PAH were more recalcitrant.

RECOMMENDATIONS AND OUTLOOK

There is potential for the re-application of this fungal strain to soil for bioremediation purposes.

Studies on mediators of manganese peroxidase for bleaching of wood pulps

In order to enhance the bleaching effect of manganese peroxidase (MnP), unsaturated fatty acids, thiol-containing compounds and various other organic compounds were applied in pulp bleaching experiments with MnP. Thiol-containing compounds did not improve the pulp bleaching effect by MnP. Some unsaturated fatty acids, linoleic acid and linolenic acid provided a better pulp bleaching effect than Tween 80. The correlation between the number of C=C bonds in a fatty acid and its pulp bleaching effect was also investigated. The MnP pulp bleaching capability was shown to depend on the carboxylic acid used. A combination of Tween 80 and a carboxylic acid resulted in higher pulp brightness than that obtained with Tween 80 alone. A laccase mediator, 3-hydroxy-1,2,3-benzotriazin-4(3H)-one, could also enhance the MnP pulp bleaching effect.

Effect of growth conditions on the production of manganese peroxidase by three strains of Bjerkandera adusta

We were looking for a strain of Bjerkandera adusta that produces high titres of manganese peroxidase under optimal conditions for large-scale enzyme purification. We have chosen two strains from the University of Alberta Microfungus Collection and Herbarium, UAMH 7308 and 8258, and compared the effects of growth conditions and medium composition on enzyme production with the well-characterized strain BOS55 (ATCC 90940). Of four types of cereal bran examined, rice bran at 3% (w/v) in 60 mM phosphate buffer pH 6 supported the highest levels of enzyme production. Using 100 mL medium in 500-mL Erlenmeyer flasks, maximum enzyme levels in the culture supernatant occurred after about 10 days of growth; 5.5 U x mL(-1) for UAMH 7308, 4.4 U x mL(-1) for UAMH 8258, and 1.7 U x mL(-1) for BOS55, where units are expressed as micromoles of Mn-malonate formed per minute. Growth as submerged cultures in 10-L stirred tank reactors produced 3.5 U x mL(-1) of manganese peroxidase (MnP) by UAMH 8258 and 2.5 U x mL(-1) of MnP by 7308, while enzyme production by BOS55 was not successful in stirred tank reactors but could be scaled up in 2-L shake flasks containing 400 mL rice bran or glucose-malt-yeast extract (GMY)-Mn-glycolate medium to produce MnP levels of 1.7 U x mL(-1). These results show that the two strains of B. adusta, UAMH 7308 and 8258, can produce between two and three times the manganese peroxidase level of B. adusta BOS55, that they are good candidates for scale up of enzyme production, and that the rice bran medium supports higher levels of enzyme production than most previously described media.

Enzymatic oxidative treatments of wheat bran layers: effects on ferulic acid composition and mechanical properties

Enzymatic treatments known to induce the gelation of feruloylated arabinoxylans solutions were applied to tissue strips isolated from peripheral layers of wheat grain to tentatively produce in situ arabinoxylan reticulation. The treatments by horseradish peroxidase (HRP) and manganese dependent peroxidase (MnP) induced a dimerization of ferulic acid (FA) in wheat bran with concomitant decrease of arabinoxylan solubility. Similar results were obtained, but to a lesser extent, by simple incubation of bran strips in water, suggesting the action of endogenous peroxidases. The fact that these treatments proved to be ineffective on the isolated aleurone layer and pericarp suggested that dimerization occurred mostly at the aleurone-pericarp interface. In addition, the MnP system generated a consumption of monomer and dimer of ferulic acid in the pericarp, perhaps due to their incorporation into lignin. Micro-mechanical tests using DMTA were performed on isolated tissue strips and showed that oxidation of wheat bran increased their mechanical strength (increase of stress and strain to rupture).

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.

Removal of estrogenic activities of bisphenol A and nonylphenol by oxidative enzymes from lignin-degrading basidiomycetes

Bisphenol A (BPA) and nonylphenol (NP) were treated with manganese peroxidase (MnP) and laccase prepared from the culture of lignin-degrading fungi. Laccase in the presence of 1-hydroxybenzotriazole (HBT), the so-called laccase-mediator system, was also applied to remove the estrogenic activity. Both chemicals disappeared in the reaction mixture within a 1-h treatment with MnP but the estrogenic activities of BPA and NP still remained 40% and 60% in the reaction mixtures after a 1-h and a 3-h treatment, respectively. Extension of the treatment time to 12 h completed the removal of estrogenic activities of BPA and NP. The laccase has less ability to remove these activities than MnP, but the laccase-HBT system was able to remove the activities in 6 h. A gel permeation chromatography (GPC) analysis revealed that main reaction products of BPA and NP may be oligomers formed by the action of enzymes. Enzymatic treatments extended to 48 h did not regenerate the estrogenic activities, suggesting that the ligninolytic enzymes are effective for the removal of the estrogenic activities of BPA and NP.