2011 Volume 18 Issue 1 Pages 18-24
In 2004, an outbreak of serious acute encephalopathy exclusively occurred in patients with chronic kidney diseases after the intake of basidiomycetous wood rotting fungus Pleurocybella porrigens. The exact factors that induced encephalopathy by this mushroom remain unknown partly due to its extreme slow growth. We attempted to develop media suitable for vegetative growth of P. porrigens for application in various fields. Fifteen isolates of P. porrigens collected from rotting conifers, Cryptomeria japonica and Pinus densiflora, in different geographical areas in Japan were cultivated on potato dextrose agar (PDA) medium; large variation in growth rate and colony features was observed among these isolates. The five isolates with the best growth rates were then cultured in five kinds of liquid media, potato dextrose (PD) medium, malt extract・yeast extract (MY) medium, potato extract・carrot extract (PC) medium, Amazake medium, and Ohta's medium at 20℃ in the dark. Dry biomasses of the isolates cultured in the liquid media were determined after 8 weeks of static cultivation. Among the tested liquid media, PD medium was the most suitable for biomass growth, followed by Ohta's, MY, Amazake and PC media. The average biomass growth of the isolates cultured in the synthetic medium (Ohta's medium) was 20-92% of that in PD medium. Remarkably large biomass variation was also observed among the isolates cultured on each liquid medium. Mycelia of this mushroom had abortive lateral branching at high frequency which could be one reason why this mushroom grows very slowly. Moreover, the Japanese population of P. porrigens has large variation in vegetative growth. Taken together, elucidation of the possible association between its chemical constituents and the onset of encephalopathy may be possible by culturing isolates with high growth ability on PD medium as a natural medium and Ohta's medium as a synthetic medium.
