Mycelium, the thread-like network forming the vegetative part of fungi, acts as the “root system” for organisms like mushrooms. Composed of individual hyphae, this network plays a role in ecosystems by breaking down organic matter and recycling nutrients. Mycelium also finds applications in mushroom cultivation, bioremediation, and sustainable materials. For researchers and cultivators, maintaining specific fungal strains over time is a common need, raising the question of whether mycelium can be frozen to preserve its viability.
The Possibility of Freezing Mycelium
Freezing mycelium is possible, but it requires careful consideration of cryopreservation challenges. Living cells, including fungi, are largely water. When water freezes, it forms ice crystals that can damage cellular structures like cell walls and membranes. This damage can lead to cell lysis, making the mycelium non-viable upon thawing.
Freezing can also cause dehydration, stressing cells. Cryopreservation aims to induce suspended animation, protecting cells from lethal damage while maintaining their potential for future growth.
Techniques for Successful Freezing
To successfully freeze mycelium and preserve its viability, specific techniques mitigate cellular damage. Cryoprotectants, such as glycerol or dimethyl sulfoxide (DMSO), are added before freezing. These compounds penetrate cell membranes, lowering water’s freezing point to prevent large ice crystals and maintain osmotic balance.
Preparing mycelium cultures, often from liquid cultures or small agar plugs, is an important step. After adding cryoprotectants, the freezing rate is carefully controlled. Slow, controlled rates, typically around 1°C per minute, are preferred to allow water to exit cells before ice forms. Rapid freezing by direct immersion in liquid nitrogen can also be effective. Once frozen, samples are stored at ultra-low temperatures, usually in ultra-low freezers at -80°C or, for long-term preservation, in liquid nitrogen dewars at -196°C.
Post-Thaw Revival and Use
After mycelium is frozen, successful revival depends on careful thawing. Rapid thawing is recommended, often by placing the cryovial into a warm water bath (30-37°C) for several minutes until completely thawed. This rapid warming minimizes damaging ice crystal formation during the transition back to a liquid state.
Following thawing, the mycelium transfers to a suitable growth medium, like an agar plate or liquid culture, to encourage recovery and active growth. Visible mycelial growth on the new medium indicates successful revival. Growth may sometimes be delayed compared to fresh cultures. Freezing and reviving mycelium allows for long-term storage of specific genetic strains, benefiting mushroom cultivation consistency, biodiversity preservation, and ongoing research.