| Budget Amount *help |
¥3,300,000 (Direct Cost: ¥3,300,000)
Fiscal Year 1998: ¥1,300,000 (Direct Cost: ¥1,300,000)
Fiscal Year 1997: ¥2,000,000 (Direct Cost: ¥2,000,000)
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| Research Abstract |
Ceriporiopsis subvermispora, a specific lignin-degrading fungus, has in recent years been used in delignifying treatments of plant biomass such as biomechanical pulping, biosulfite pulping and digestibility enhancement of forage grasses. This fungus is known to decompose lignin located in wood cell walls and middle lamellae without erosion of the wood cell walls even after fiber separation. Taking into account that hyphal growth and excretion of enzymes takes place in the lumen and that enzymes are too large to penetrate pores of wood cell Walls, it can be concluded that some kind of diffusible low molecular weight compounds are produced by the fungus, leading to the degradation of lignin at the site far from enzymes. In the biomechanical pulping with C.subvermispora, high energy saving effect was obtained with a short incubation period of 2 weeks, indicating that middle lamellae were damaged for the first 2 weeks. After 6 weeks cultivation, corresponding to 15-20 percent weight loss,
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fiber separation by the lignolysis of middle lamellae can be observed by microscopy. Thus, extensive damage of middle lamellae in the early stage of wood decay by C.subvermispora cannot be understood by the simple radical transfer system from cell lumina into wall regions. Based on this discussion, we focused on the free radical generation system inside of wood cell walls. In this study, peroxidizable low molecular mass compounds produced by C.subvermispora were analyzed by GC-MS, NMR and ESR spectroscopy. As a result, it has been found that C.subvermispora produced free unsaturated fatty acids (USFA), 9,12- octadecadienoic, 11-octadecenoic and 9-octadecenoic acids, together with saturated fatty acids (SFA) octadecanoic and hexadecanoic acids on wood meal cultures. The fractions containing USFA and SFA were oxidized with soybean lipoxygenase and the free radicals formed by the enzymatic peroxidation were analyzed by spin-trapping with 4-POBN.ESR spectra showed that strong radicals were generated from the extract obtained at the early stages of cultivation (8-12 days). However, signal intensities of the spin adducts did not increase after prolonged cultivation (16-28 days). Hyperfine coupling constant and g-value of the major spin adduct were identical to those of pentyl radical. These results strongly suggest that the free unsaturated fatty acids did not originate from fungal hypha but from extracellular metabolites of the fungus related to lignin biodegradation. Production of lipid hydroperoxide by this fungus was also demonstrated by DPPP assay. Less
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