THE ROLE OF FUNGUS-FIBER CONTACT IN THE BIOBLEACHING OF KRAFT BROWNSTOCK BY TRAMETES (CORIOLUS) VERSICOLOR

Recently the white-rot basidiomycete Trametes (Coriolus) versicolor was shown to be capable of producing a substantial brightness increase in unbleached kraft pulp with no loss in paper strength properties. This brownstock bleaching presently requires 4-5 days and optimization of the system is greatly hampered by our ignorance of the mechanism of lignin biodegradation and modification. An essential step in understanding this process is determining whether physical contact between pulp fibers and fungal hyphae is necessary. Simple addition of active biobleaching liquors to brownstock slurries resulted in little or no bleaching. Because of the great facility with which both pulp and fungal hyphae clog microporous filters, a device capable of automatically cycling between filtration and filter backflushing was constructed. Using this controlled exchange apparatus, it was shown that T. versicolor is capable of carrying out biological bleaching in the absence of physical hyphal-fiber contact. This suggests that the filterable liquor in the biobleaching system contains all the components needed for delignification of kraft hardwood brownstock. Thus, if fungal production of these components proves to be rate-limiting, biobleaching may be substantially accelerated. Furthermore, the biobleaching mechanism can be more easily dissected and understood than if intimate fungal-fiber contact is necessary.