Mycelium, the intricate network of hyphae, represents the primary vegetative body of a fungus. This vast web spreads through substrates like soil or wood, acting much like the root system of a plant. Mycelium plays a fundamental role in ecosystems by breaking down organic matter and recycling nutrients. Beyond its ecological importance, mycelium is crucial for human interests, forming the basis of edible mushrooms and finding innovative uses in biotechnology, such as creating sustainable biomaterials.
Mycelium’s Preferred Environment: Optimal Growth Temperatures
Mycelial growth thrives within specific temperature ranges, though these vary by fungal species. Many cultivated mushroom species exhibit optimal growth between 20°C and 25°C (68°F and 77°F) during colonization. For instance, oyster mushroom varieties colonize best between 24°C and 29°C (75°F and 85°F). Shiitake mycelium prefers 21°C to 24°C (70°F to 75°F), while Lion’s Mane grows best between 18°C and 24°C (65°F and 75°F). Maintaining these consistent conditions is important for robust mycelial expansion and successful mushroom cultivation.
The Thermal Death Point: When Mycelium Dies
Mycelium cannot survive beyond a certain temperature threshold. While optimal growth for many species occurs around 25°C (77°F), mycelial growth can slow or halt as temperatures approach 35°C (95°F). The exact temperature at which mycelium dies, known as its thermal death point, is not fixed and depends on heat intensity and duration.
Different fungal species exhibit varying tolerances to high temperatures. Some oyster mushroom mycelium can tolerate brief heat spikes, but prolonged exposure above 36-37°C (96.8-98.6°F) for over 24 hours can lead to death. Research indicates the thermal death point for edible mushroom species ranges broadly: Flammulina sp. (Enoki) at 37.6-39.4°C, Agaricus bisporus (Button) between 39.4-48.4°C, and Pleurotus spp. (Oyster) from 43.0-50.2°C. Shiitake mycelium dies around 38°C (100°F), though other strains show lethal points up to 50.2°C. Exceeding optimal temperatures, even if not immediately lethal, can also promote undesirable bacteria, which outcompete the mycelium.
Factors Influencing Mycelial Survival and Death
The precise temperature at which mycelium perishes is influenced by several factors. Fungal species exhibit inherent variations in heat tolerance, reflecting their adaptations. The duration of exposure to elevated temperatures is significant; a short burst of high heat might be tolerable, but prolonged exposure can be fatal.
Moisture content impacts how heat is transferred and absorbed, affecting susceptibility to thermal damage. While dormant spores are more resistant, actively growing mycelium is more vulnerable. Healthy mycelium with ample nutrient availability tends to be more robust against suboptimal temperatures. Mycelium generates its own metabolic heat during colonization; if not properly ventilated, internal substrate temperature can rise, causing damage or death.
Applying the Knowledge: Temperature Control in Mycology
Understanding mycelium’s temperature tolerances is fundamental to mycology and cultivation. In mushroom cultivation, temperature control is important for preparing substrates and managing growth. Pasteurization, a common method, involves heating the substrate to 60-80°C (140-176°F) for one to two hours, which reduces harmful microorganisms while preserving some beneficial ones. For complete elimination of all microorganisms, sterilization is employed by heating above 121°C (250°F) under pressure.
During colonization, growers maintain incubation temperatures, generally between 20-25°C, to encourage rapid mycelial spread. For mushroom formation (fruiting), temperatures are often lowered, mimicking natural environmental cues. This precise temperature management is also a strategy for preventing contamination, as many common molds and bacteria thrive at temperatures outside the mycelium’s preferred range. Beyond cultivation, research into thermal thresholds advances fungal biology understanding. In industrial applications, like biomaterial production, controlled temperatures are important for processing, including drying at 50-100°C and managing decomposition that begins around 225-300°C.