Coprinus comatus is known to be a phylogenetically diverse species and multiple mating types have been reported; thus, it is necessary to reconsider the mating system of Japanese C. comatus. Our phylogenetic analysis, based on the ITS region, revealed that this species could be divided into three clades, and Japanese C. comatus was placed into a single clade. Homokaryons isolated from the fruiting body of C. comatus showed that the mating system was bipolar heterothallism. No A incompatibility factor recombinant was found, suggesting that factor A is composed of two extremely close subunits on the same chromosome. On the other hand, heterokaryons and homokaryons can be distinguished by the frequency of clamp formation. The frequency of clamp formation in heterokaryons was 30% or more, while that of homokaryons was 8% or less. Moreover, it was suggested that the ability to form clamp cells in the homokaryons was not genetically linked to mating-type locus.

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Hericium erinaceum (Yamabushitake) is an edible mushroom that has been reported to display various pharmacological activities, including neuroprotective, anti-inflammatory, and antioxidant effects. In this study, we found that the water extract of H. erinaceum inhibited biofilm formation of the periodontopathogenic bacterium Eikenella corrodens; however, no inhibitory effect was observed with the methanol extract. Moreover, the biofilm inhibitory effect of H. erinaceum was observed in a dose-dependent manner and was not due to bactericidal activity against E. corrodens. H. erinaceum extract was fractionated by ammonium sulfate precipitation and biofilm inhibition was achieved with the 70% fraction. Heat treatment of the 70% fraction did not completely prevent biofilm inhibition, suggesting that partially heat-stable proteins are involved in the biofilm inhibition. Further fractionation of the 70% fraction by ultrafiltration indicated that the biofilm inhibitor may be a protein with a molecular weight of approximately 60 to 100 kDa. It is also suggested that H. erinaceum extract could degrade the biofilm once formed.

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For the cultivation of Shiitake (Lentinula edodes) on log woods cultivated in laying yards contaminated by radioactive matter, we examined the movement of radiocesium in the log woods and the effectiveness of radiocesium remediation measures. Shiitake mushrooms grown on radiocesium-contaminated logs treated with nanoparticle insoluble Prussian blue (NPB) showed lower radioactivity than those grown on untreated radiocesium-contaminated logs. For log woods with radiocesium concentration of approximately 250 Bq/kg soaked in NPB dispersion liquid, the radiocesium concentration of harvested fruit bodies was 40 Bq/kg or less. In a second experiment, the use of a cesiumsorb filter (CSF) sheet as an overlay on a radioactive matter-contaminated laying yard (spatial dose rate, 0.19 mSv/h) produced a significant decrease in radiocesium in the fruit bodies after 15 to 18 months compared to placing bed logs directly on contaminated soil (with CSF sheet, 4.0 ± 1.8 Bq/kg; directly on contaminated soil, 7.8 ± 4.0 Bq/kg). Furthermore, CSF sheet was shown to specifically adsorb radiocesium from soil (soil, 764 Bq/kg; CSF sheet, 4,735 Bq/kg). Our findings will contribute to the promotion of good practices for Shiitake mushroom cultivation.

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Establishing a model strain can be an effective means to research the fruiting body formation of mushrooms using genetic approaches. Pleurotus salmoneostramineus L. Vass is known for its pink color. The mushroom is easy to cultivate in the laboratory, and it develops a clear pink color when the primordia are formed. By morphological observation of hyphae and fruiting bodies, and the compatibility test, it was revealed that it is a quadrupolar mushroom with a heterothallic lifecycle. Here, we screened monosporous strains isolated from P. salmoneostramineus NBRC31859. Among these, 30 strains showed a variety of mycelial and fruiting types, and monokaryotic strains N81 (non-fruiting) and N13 (fruiting) were selected as model strains for fruiting mechanism experiments based on their similar mycelial growth rate and colony morphology.

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We purified and characterized the polygalacturonase LePG28A from white-rot fungus Lentinula edodes. LePG28A had endo-type polygalacturonase activity, with maximum activity at 70℃ and pH 4.0. In acetate buffer, the enzyme showed activity against sodium polygalacturonate and polygalacturonic acid, but did not degrade calcium polygalacturonate gel. Pectic substances of the wood cell wall are cross-linked by calcium ions, indicating that LePG28A cannot degrade this calcium polygalacturonate gel directly. On the other hand, LePG28A disintegrated calcium polygalacturonate gel in oxalate buffer. This suggests that the enzyme showed synergistic action with oxalic acid in the degradation of calcium polygalacturonate gel. Therefore, oxalic acid has a role in the chelating of calcium ions from pectic substrates.

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Trehalose is a non-reducing disaccharide in which two molecules of glucose are linked by an a, a-1,1 glycosidic bond, and it is one of the most abundant sugars in mushrooms. Since the trehalose content of shiitake mushrooms (Lentinula edodes) tends to increase during the warm-air drying process, the trehalose content of shiitake was investigated in detail. About five strains of log-cultivated shiitake mushrooms, the trehalose content of the shiitake dried at a constant temperature of 50°C was higher than that of fresh shiitake, while there was no significant difference in glucose content. The trehalose content of shiitake increased linearly until 2 hours after the start of drying, and then continued to increase gradually until 48 hours during the drying process at a constant temperature of 50°C. Comparisons of the trehalose contents of shiitake mushrooms after drying at the 40°C, 50°C, and 60°C revealed that the trehalose contents were the highest in the shiitake dried at 40°C, and lowest in the shiitake dried at 60°C.

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Since ancient times, the anomalous occurrence of mushrooms around lightning strikes has been confirmed. Based on this phenomenon, various shiitake mushroom cultivation methods with lightning strikes using cultivation bed logs (wood) have been proposed. One remarkable related work reported that the fruiting capacity of shiitake mushrooms was significantly promoted by directly applying a high voltage to the cultivation bed log1). However, mushroom bed logs are rarely struck by lightning directly in the natural environment. Therefore, this method does not match the conditions in the natural environment. We performed lightning strike experiments using a new method that considers the natural environment. This new method delivers a thunderbolt to a lightning rod using the electric discharge created by an impulse voltage generator, but it does not apply lightening directly to the cultivation bed log. The cultivation bed logs are placed a few meters away from the lightning rod in order to replicate the natural environment. In this experiment, we compared the fruiting capacity of shiitake mushrooms with and without simulated lightning strikes. From the experimental results, in the case of simulated lightning strikes, twice the number of shiitake fruiting bodies was harvested compared with the case without simulated lightning strikes. Moreover, this result clearly specifies that even though a high voltage was not applied directly, increased production of shiitake mushrooms by lightning strikes was confirmed.

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The hydrophilic antioxidant capacities of 10 common edible mushroom species consumed in Japan were measured using the hydrophilic oxygen radical absorbance capacity (H-ORAC) method. The mushroom varieties were collected from multiple production areas and sites. Agaricus bisporus showed the highest activity (1657 mmol Trolox equivalent/g fresh weight), followed by Pleurotus ostreatus, then Flammulina velutipes, then Tricholoma matsutake. The antioxidant capacities of Hypsizigus marmoreus, Lentinula edodes, Grifola frondosa, Pleurotus eryngii, Pholiota nameko, and Auricularia polytricha were also assessed. As edible mushrooms are usually consumed after cooking, the antioxidant capacities after boiling were also measured. The average reduction in antioxidant capacity was 11.1%, indicating that edible mushrooms retain significant hydrophilic antioxidant capacity after boiling for 5 min.

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