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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 MnSO4, Tween 80, and sodium malonate with continuous addition of H202 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. Some white rot fungi are known to selectively degrade lignin in wood. The residual lignin in kraft pulp is highly modified by alkaline condensation reactions; nevertheless, some fungi can delignify unbleached hardwood kraft pulp (1, 4, 16) and softwood kraft pulp (5, 20). Biobleaching with white rot fungi, including Trametes (Coriolus) versicolor (1, 16, 20) and fungus strain IZU-154 (4, 5, 14), has been studied by workers in some laboratories, who sought to eliminate or reduce the use of chlorine-based chemicals in bleaching. The extracellular ligninolytic enzyme system of Phanerochaete chrysosporium has been studied extensively in recent years. We know that lignin peroxidase (LiP), manganese peroxidase (MnP), and laccase are enzymes that are associated with the degradation of lignin. There have been several reports of using in vitro enzyme treatments to bleach hardwood kraft pulp. Arbeloa et al. showed that treatment of unbleached kraft pulp with LiPs facilitated subsequent chemical bleaching (2). Bourbonnais and Paice demonstrated that unbleached kraft pulp was delignified with isolated laccase from T. versicolor in the presence of 2,2-azinobis-(3-ethylbenzthiazoline-6-sulfonate) and that methanol was released (3). It has also been reported that delignification of hardwood kraft pulp by MnP was observed, but the extensive brightening observed with the fungus was not achieved with MnP (17). Recently, we showed that MnP plays an important role in the bleaching of unbleached hardwood kraft pulp by white rot fungi (7). Furthermore, we developed a cultivation system in which a membrane filter was used to prevent direct contact between hyphae and kraft pulp while allowing extracellular enzymes to attack the kraft pulp. By using this system we found that the level of secreted MnP activity in the filterable components was substantial during in vitro bleaching with Phanerochaete sordida YK-624 (9). Therefore, in this study, we examined in vitro bleaching of kraft pulp with MnP isolated from strain YK-624. MATERUILS AND METHODS Fungi. Fungus strain YK-624 (= ATCC 90872), which was isolated from decayed wood obtained from a forest and was identified as P. sordida (9), exhibited remarkable bleaching

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We devised a screening method to obtain basidiomycetous fungi capable of degrading dioxins. About 200 fungal strains were selected from more than 1500 strains by their ability to decolorize Remazol brilliant blue R dye as an indicator. To attempt to eliminate the factor of dioxin sorption by mycelia, we prepared two series of living cultures exposed either long term or short term to 2,7-dichlorodibenzo-p-dioxin (2,7-DCDD), and compared the decreases in the levels of this chemical. In only 11 strains was there a significant difference between the two treatments. We chose Panellus stypticus strain 99-334 as a new, effective dioxin degrader, because it gave a close to 100% decrease in 2,7-DCDD levels (from an initial concentration of 10 microM) after 40 days of exposure. The detection of a metabolic intermediate (1-chloro-3,4-dihydroxybenzene) by gas chromatography-mass spectrometry analysis supported the ability of this strain to degrade 2,7-DCDD.

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 4 in the presence of oxalate, malonate, or gluconate as manganese chelator. When the pulp was treated without the addition of MnSO 4 , 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 4 in the presence of malonate than in the presence of oxalate. Oxalate reduced MnO 2 which already existed in the pulp or was produced from Mn 2؉ by oxidation with MnP and thus supplied Mn 2؉ to the MnP system. The presence of gluconate, produced by the H 2 O 2-generating enzyme glucose oxidase, also improved the pulp brightness without the addition of MnSO 4 , 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.