A new method for the preservation of fungus stock cultures by deep-freezing

Abstract

Recovery of 66 fungus stock cultures including Oomycota, Zygomycota, Ascomycota, Basidiomycota, and mitosporic mycetes were examined after cryopreservation. Almost all the stock cultures remained viable when the mycelia that had grown over the sawdust medium containing 10% glycerol as the cryoprotectant (65% moisture content, W/W) were frozen rapidly at −85°C and then allow to thaw naturally at room temperature. Test stock cultures were preserved for more than 10 years by this preservation method without any programmed precooling and rapid thawing for their cryopreservation. Most of the test fungi could survive for 5 years in medium containing 10% glycerol even after alternate freezing and thawing at intervals of 6 months. When a strain of Flammulina velutipes was tested for mycelial growth rate and productivity of fruit-bodies after cryopreservation for 3 years, the fungus reproduced with its initial capability. These results demonstrate that the sawdust-freezing method using a cryoprotectant is expected to be a reliable and easy preservation method for fungus stock cultures.