Influence of Strain Preservation Methods on Fruiting Body Growth and Metabolite Production by the Medicinal Mushroom Cordyceps militaris (Ascomycetes)

Cordyceps militaris is a highly valued edible and medicinal fungus because of its production of various metabolites including adenosine, cordycepin, and N6-(2-hydroxyethyl)-adenosine. Fruiting bodies of this fungus have been used successfully in industrial production and widely as a substitute for Ophiocordyceps sinensis (syn. C. sinensis) in traditional Chinese medicine and health supplements. Strain degeneration occurs with high frequency during the subculturing and preservation of C. militaris strains, which leads to significant losses during industrial production. In this study, we evaluated the effects of different strain preservation methods on fruiting body growth and metabolite production. We found that strain degeneration affects not only fruiting body differentiation but also metabolite production, and suitable preservation methods can avoid degeneration. Preservation in sterile water has a similar effect as cryopreservation in liquid nitrogen at -196°C with regard to maintaining the characteristics of C. militaris strains for at least 1 year, and it is a practical and satisfactory method for preserving C. militaris strains that can be used in factories. Ultracold freezing at -80°C is not suitable for this fungus. Lyophilization, which causes C. militaris strains to retain their inherent characteristics and avoid degeneration, is suitable for long-term preservation (at least 4 years). This study provides practical preservation methods for C. militaris strains over the short and long term and will be helpful to achieve stable and superior-quality production of C. militaris fruiting bodies.