Fungi, which include molds, yeasts, and mushrooms, represent a diverse kingdom of organisms with a unique relationship to their environment. A mushroom is simply the fruiting body of a larger, hidden fungal network called the mycelium. The scientific curiosity lies in how these organisms, evolved under Earth’s constant gravity, manage fundamental processes like growth orientation and spore dispersal in the microgravity of space.
Fungal Biology and the Role of Gravity
Fungi thrive by breaking down organic matter, requiring a substrate for nutrients, sufficient moisture, and oxygen. Cultivated mushrooms prefer a substrate moisture content of 60% to 75% and high humidity (80% to 95%) to support mycelial colonization and fruiting. They also need specific temperature ranges, typically between 55°F and 75°F, which vary by species, and generally prefer dark or low-light conditions.
On Earth, the mushroom’s development is governed by gravitropism, a growth response to gravity. This mechanism ensures the stalk, or stipe, grows directly upward and the spore-bearing surface, such as gills or pores, is perfectly vertical. The upward growth of the stipe is negative gravitropism, while the precise downward orientation of the spore-releasing structures is positive gravitropism.
Fungi use specialized structures within their cells to sense gravity, though the exact components are species-specific. For some, the cell nucleus, connected to the cytoskeleton, may act like a tiny sedimenting weight. Other fungi, like the pin mold Phycomyces blakesleeanus, use dense, octahedral protein crystals that settle within fluid-filled compartments to determine orientation. This physical sedimentation triggers a signal that directs differential cell elongation, allowing the mushroom to curve and reorient itself.
Spaceflight Experiments and Findings
Early spaceflight experiments tested fungal viability by exposing spores and mycelial cultures to microgravity. Studies show that the mycelium can generally grow in microgravity, but the lack of gravity profoundly affects its structure and function. For instance, the mycelial network tends to grow in a more spherical, less directional pattern without gravity to guide it.
Specific organisms like the mold Aspergillus niger have been included in studies like the Artemis I mission to understand their resilience to deep space radiation and microgravity. Other fungi, such as Aureobasidium pullulans, have survived for two years in the harsh environment near the International Space Station (ISS). This indicates a high tolerance for extreme conditions, including desiccation and radiation exposure.
Experiments involving species like Candida albicans, a pathogenic yeast, show that microgravity alters gene expression in fungal cells. This change affects properties like cell aggregation, biofilm formation, and resistance to stresses, which has implications for astronaut health. While fruiting bodies may form in microgravity, the precise orientation required for effective spore dispersal is lost without gravity sensing. Recent ISS experiments are also studying medicinal species, including Lion’s Mane, Turkey’s Tail, and Cordyceps, to observe how their networks grow and adapt.
Applications of Fungi in Space Exploration
The potential for fungi to adapt and thrive in space makes them valuable candidates for sustaining long-duration missions. One primary area of research is “myco-architecture,” which uses the fungal mycelium as a self-assembling, biological building material. Astronauts could carry a lightweight scaffold infused with dormant fungi to a destination like Mars or the Moon, then activate the fungus by adding water and nutrients.
As the mycelium grows, it colonizes the framework, forming a dense, fibrous network that hardens into a robust, lightweight structure for habitats. This technology eliminates the need to transport heavy construction materials from Earth, saving cargo weight and cost. Myco-composites developed for this purpose have also shown promise in radiation shielding, offering protection against the harsh cosmic radiation environment.
Fungi also offer solutions for closed-loop life support systems through bioremediation and waste recycling. Fungal processes break down organic waste, such as food scraps and plant biomass, converting them into useful resources. This conversion can produce bioplastics, nutrients, and mycoprotein, which could serve as a sustainable food source for future space colonists. Integrating fungal systems into spacecraft helps maintain clean air and water using their networks for biofiltration, reducing reliance on heavy mechanical systems.