Higher fungi such as wood rotting basidiomycota and entomopathogenic ascomycota fungi are known to form fruiting bodies to release spores. These fungal mycelia work as decomposers in ecological systems. Therefore, these higher fungi have excellent degradation potential for aromatic and aliphatic polymers, such as lignin and cuticles. There have been many reports on the degradation of organic pollutants utilizing such higher fungi. In addition to these reports, we have demonstrated that some wood rot fungi and plant worm fungi are able to degrade persistent organic pollutants (POPs), such as dioxins, their congeners, and chlorinated pesticides, in addition to polyaromatic hydrocarbons and neonicotinoid insecticides. It has also been suggested that cytochrome P450 enzymes are able to carry out the initial reaction of many degradation processes, thereby modifying the structure of these pollutants and reducing the toxicity. Furthermore, we discovered that the edible mushroom Pleurotus ostreatus and the medicinal mushroom entomopathogenic fungus Cordyceps militaris have the ability to degrade DDT and PAHs in soil, respectively. As mentioned above, higher fungi including mushrooms are able to metabolize several environmental POPs; therefore, applications using fungal mycelium such as spent mushroom substrate for bioremediation are expected to result from further study in this field.
Tricholoma matsutake NBRC 30605 shows xylan-degrading activity when cultured in xylan-supplemented medium. In the present study, we purified a xylan-degrading enzyme to homogeneity. The molecular mass of the enzyme was found to be 81 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and 88 kDa by size-exclusion chromatography. The purified enzyme showed maximum activity at a temperature of 55℃ and pH 4.0. The enzyme was completely stable at temperatures up to 30℃ and at pH 3.0 － 4.0. Km and Vmax values of the purified enzyme against p-nitrophenyl β-D-xylopyranoside were 1.28 mM and 14.45 U/mg, respectively. The enzyme released xylose from β-1,4-linked xylo-oligosaccharides with chain lengths of 2 to 5 and beechwood xylan. Treatment with 10 mM MnCl2 (29%), ZnCl2 (28%), NiCl2 (29%) and with 5 mM EDTA (15%) strongly inhibited the activity of the purified enzyme. The N-terminal amino acid sequence of the enzyme was identical to that of the deduced amino acid sequence of T. matsutake β-xylosidase. These findings indicate that the purified enzyme is a xylan-degrading β-xylosidase belonging to the glycosyl hydrolase family 3.
To utilize residual enzymes in dried mushrooms as enzyme preparations, we determined the β-glucosidase activity in 5 species of dried edible mushrooms that were purchased fresh. The enzyme activity in dried shiitake (Lentinus edodes) was higher at 37℃ than at 60℃, but the activity in dried maitake (Grifola frondosa) and bunashimeji (Hypsizygus marmoreus) was higher at 60℃ than at 37℃. After storage for 1 year, enzyme activity was detected in all dried mushrooms tested, and was best preserved in dried eringi (Pleurotus eryngii) and bunashimeji. To examine the effect of heat during drying on the enzyme activity, we checked two methods of drying; oven drying, used for preparation of dried shiitake, and vacuum drying. Just after preparation of dried mushrooms, the activity in the vacuum-dried mushrooms was higher than in oven-dried mushrooms. But one year after preparation, the activity was almost the same for both types of dried preparations. The residual enzymes in the oven-dried mushrooms were stable, suggesting that the same drying method and oven used for dried shiitake preparation will be applicable for production of dried mushrooms as enzyme preparations.
In this study, the effect of grain size of Salix udensis sawdust on the fruiting bodies of Lentinula edodes was investigated through experimental cultivation. Sawdust sorted into four grain sizes was used for each treatment, and unsorted sawdust was used for the control. Compared to the control and other grain sizes, the yield of fruit-bodies with a commercial value (i.e. fruit bodies larger than M size) was higher when using sawdust with a grain size of 0.5 to 1.0 mm. This result indicates that adjusting willow sawdust grain size further enhances the potential usefulness of willow for sawdust-based cultivation of L. edodes.