A Possible Role of Manganese Peroxidase during Biobleaching by the Pulp Bleaching Fungus SKB-1152

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 M added Mn to below the detection limit of 0.26 M Mn in EDTA-extracted pulp medium. The lowest Mn concentration tested was at least several orders of magnitude lower than the K m 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.

mentioning

confidence: 98%

“…However, there is increasing evidence that MnP is required for bleaching. MnP is generally detected in active biobleaching cultures (21,25,40). The peak production of MnP has been reported to coincide with the time period in which pulp biobleaching occurs (25,40).…”

mentioning

confidence: 99%

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

Moreira

Sierra-Álvarez

Lema

et al. 1997

“…Recently, some reports have shown that MnP plays an important role in the bleaching of unbleached hardwood kraft pulp by white rot fungi (15,17,19,23,33). MnP, first discovered in Phanerochaete chrysosporium (26,34), is known to be secreted by many lignin-degrading fungi, including T. versicolor (18,33), P. sordida (41), and others (31,35). MnP is a heme-containing enzyme and oxidizes Mn 2ϩ to Mn 3ϩ , which chelated with an organic acid, in turn oxidizes phenolic substrates, including lignin model compounds (47)(48)(49), dehydrogenative polymerizate (50), and high-molecular-weight chlorolignin (27,30).…”

mentioning

confidence: 99%

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

Harazono¹,

Kondo²,

Sakai³

1996

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.

“…A partial correlation between MnP activity and biobleaching has been found in several screening programs (2,21,40). In time course experiments, the occurrence of MnP coincides with the period of maximum brightness gains and delignification (23,43). MnPdeficient mutants of the best-characterized biobleaching species, Trametes versicolor, are not able to cause bleaching, and the bleaching activity can be restored by the exogenous addition of MnP (3).…”

mentioning

confidence: 97%

Role of Organic Acids in the Manganese-Independent Biobleaching System of Bjerkandera sp. Strain BOS55

Moreira

Mester²,

Mayorga³

et al. 1998

Bjerkandera sp. strain BOS55 is a white rot fungus that can bleach EDTA-extracted eucalyptus oxygen-delignified kraft pulp (OKP) without any requirement for manganese. Under manganese-free conditions, additions of simple physiological organic acids (e.g., glycolate, glyoxylate, oxalate, and others) at 1 to 5 mM stimulated brightness gains and pulp delignification two- to threefold compared to results for control cultures not receiving acids. The role of the organic acids in improving the manganese-independent biobleaching was shown not to be due to pH-buffering effects. Instead, the stimulation was attributed to enhanced production of manganese peroxidase (MnP) and lignin peroxidase (LiP) as well as increased physiological concentrations of veratryl alcohol and oxalate. These factors contributed to greatly improved production of superoxide anion radicals, which may have accounted for the more extensive biobleaching. Optimum biobleaching corresponded most to the production of MnP. These results suggest that MnP from Bjerkandera is purposefully produced in the absence of manganese and can possibly function independently of manganese in OKP delignification. LiP probably also contributed to OKP delignification when it was present.