Analysis op-oxidation mchanism of white rot fungi that promate lignin degradation by addition of polyisoprene rubber ; Application to resurce conversion and bioremediation

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Recycling of vulcanized synthetic and natural rubbers is important to avoid environmental problems due to accumulation of the undegradable polymers. To achieve this purpose, degradation of polysulfide bonds in vulcanized rubber is necessary. In this research, we found that a white rot fungus, Ceriporiopsis subvermispora aggressively degraded vulcanized natural rubber sheets (NRS) in the presence of wood. During the cultivation, we also found that addition of NRS markedly accelerated degradation of lignin in the wood. Scanning electron microscopy clearly demonstrated that the surface of the NRS treated by C. subvermispora was intensively damaged. The degradation of NRS was also analyzed by elemental analysis, ESCA and DD/MAS ^<13>C NMR. These analyses demonstrated formation of S-O bonding and decrease in the number of S-C linkage. The fungus preferentially attacked cis-monosulfide bonds. In the degradation of wood by C. subvermispora lipid peroxidation catalyzed by manganese peroxidase (MnP) play a central role. Therefore, MnP was reacted with a fungal metabolite of this fungus, linoleic acid, and the reaction products formed were analyzed by ESR and GC-MS. MnP oxidized linoleic acid to produce acyl radicals. In this reaction, glyoxal was produced as a major aldehyde. The reaction produced chemiluminescent chemical species that is different from singlet oxygen, triplet carbonyl and biacyl triplet. Fluorene and polyisoprene was not degraded by the glyoxal/ MnP system but oxidized by linoleic acid / 1MnP. Thus, aldehyde oxidation was effective for the propagation of chain reactions but the reaction did not produce highly oxidative chemical species. Further research on the mechanisms of free radical reactions is important to establish a new biological and chemical recycling method of rubber.