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 delignif ied 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 brig htness 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 nut rient 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 co ncentration 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 t he predominant oxidative enzyme produced even under culture conditions in the near absence of manganese, High nitrogen (22 mM N) and exogeno us veratryl alcohol (2 mM) repressed biobleaching in Mn-deficient but not in Mn-sufficient culture medium, No correlation was observed betwe en the titers of extracellular peroxidases and the biobleaching. Howev er, the decolorization rate of the polyaromatic dye Poly R-478 was mod erately correlated to the biobleaching under a wide range of Mn and N nutrient regimens.