by Tristan Wang

Hollywood movies and horror novels have painted extraterrestrial life as green monsters, scouring the barren grounds of Mars and shooting any intruder with photon lasers. These disturbing imaginations, while far-fetched, do hold some truth about frightening outer space life forms, but not in the ways we imagine. During its orbit as the first modular space station, the satellite Mir experienced attacks from the least suspect extraterrestrial life form: mold. Splotches of fungal hyphae covered windows and control panels and gradually ate away at the hull’s interior during the latter part of the satellite’s life, and with it, any notion of a “sterile spaceship”.1

The discipline of astrobiology attempts to answer the larger mysteries about life: its origin, necessities for survival, and presence in other worlds. But astrobiology also has practical applications in considering how biological organisms may travel through space. In particular, human space travel would greatly benefit from studying a branch of fungal biology known as astromycology: the study of earth-derived fungi in space. Fungi offer both an opportunity and threat to human space travel. Problems arising from fungal intruders are both wide and relevant, ranging from providing food and decomposing biological material to breaking down spacecrafts. Interactions of intense radiation and lack of gravity with fungal growth underlie the opportunities and threats that fungi pose to human space travel.

Ecology

Environments in orbiting spacecrafts are often different from terrestrial environments back on Earth due to the lack of gravity and higher radiation levels in outer space. Even given these obstacles, fungi seem to have found a way to inhabit space environments. The Mir spacecraft was reported to host several general of fungi including species of Aspergillus, Penicillium and Cladosporium, all of which are known to be common molds of the phylum Ascomycota.1 What makes these genera so special is their adaptability to survive in a variety of environments. These genera are known as saprophytes (organisms that live on decaying matter) and are shown to be resilient in a relatively wide range of temperatures and humidities.2,3 Thus, food and environments are not as limiting to these opportunistic fungi, organisms able to spread quickly into uncolonized environments.

Fungi and plants have been shown to display the phenomenon of gravitropism, growth in reaction to gravity. Being able to grow in a particular direction is important for fungal development, in particular for reproduction and spore discharge. For example, in the case of ascomycetous fungi, sexual spores are discharged into the air through tubular vesicles called asci.4 If fruiting bodies of molds release spores towards the base of the aerial hyphae, reproduction would not be optimized. Also, studies have shown that fungi tend to respond most sensitively to gravity just behind the apex of growing hyphae, which are hair-like filaments of fungi, although there seems to be a significant lag time before a notable reaction.5 It has been proposed that this bending of hyphae is due to a particular chemical growth factor that originates from the apical portion of the stem.6

Whereas gravity affects the morphological shape of fungi, radiation is more subtle in its physiological impact. Fungi seem to have peculiar adaptations to coping with stress due to radiation. Scientists have studied closely how radiation from the nuclear meltdown at Chernobyl in 1986 affected the environment and its ecology. Darkened fungal organisms were retrieved from the reactor’s walls.7 Specifically, these fungi were melanized, which means they were darkened by natural pigments.

Typically, fungi are fairly resistant to exposure to doses of ionizing radiation and it appears that the morphological adaptation of melanin reinforces this defense.8 Melanized fungi occur naturally around the world from the arctic to the Antarctic but when researchers observed Penicillum expansum in space for seven months, they observed increased presence of melanin layers.8 In fact, Cryptococcus neoformans cells exposed to radiation 500 times the background rate grew faster than irradiated non-melanized and non-irradiated counterparts.8 It is possible that melanin not only protects free radicals from harming important fungal DNA, but also provides some mechanism of energy utilization similar to how plants capture light energy.8 Indeed, some studies have shown an increased rate of metabolism for melanized fungi when irradiated. The basis for fungal resistance to ionizing radiation may be genetic. Expressions of genes related to cell cycle and DNA processing seem to be sensitive to upregulation when irradiated and may help the organism adapt better to the environment.8

Implications for Human Space Travel

Perhaps one of the better-known uses of fungi in space comes from edible mushrooms. It’s not unusual for foodies and nutritionists to have positive reviews over the nutritional and delicacy of general fungal-based foods. Typically, edible mushrooms are rich in protein, complex carbohydrates and certain vitamins such as D (in the form of ergosterols) and some B vitamins while being low in fat and simple carbohydrates.9 The Food and Drug Administration (FDA) even ranks mushrooms as “healthy foods” which raises the question of cultivating mushrooms as a sustainable food source in space.9 A popular edible mushroom Pleurotus ostreatus, also known as the oyster mushroom, has proven useful in its versatility in cultivation. While edible mushrooms are able to feed off of a variety of lignocellulosic substrates, P. ostreatus requires a shorter time to grow and has a high fruiting body to substrate ratio when developing.10 All these factors make oyster mushrooms one of the most cultivated edible mushrooms, and a good candidate for use in space.10

The greatest strength of fungi in breaking down materials also happens to be its greatest fallback. Common fungi that find homes in house-fridges also happen to be adept in forming corrosive secondary compounds. Common genera found in spacecraft and on Earth like Geotrichum, Aspergillus, and Penicillum create destructive compounds capable of hydrolysis like acetic acid.11 This chemical component, coupled with hyphe (mycelial root-like hairs of fungi) penetration, allows fungi to damage deep into surface layers like wood, stone and walls.1,11 Not surprisingly, given the variety of substrates fungi can colonize, space crafts are not impermeable to an infestation.

Conclusion

At home, molds are considered a pest growing in our bathrooms, wet corners of houses and in old refrigerators. In nature, it seems that mushrooms play an integral part in the cycle of nutrients breaking down lignin and other plant material. Out in space, however, we are just beginning to learn about fungal presence. Fungal interaction with gravity and radiation seem to come right out of a science-fiction novel, but their implication as a nutritional and yet destructive entity is real. People have looked for extra-terrestrial life for generations, and it seems that only now are we noticing the most interesting, important and fuzzy aliens so far. Perhaps one day, scientists will find a way of incorporating fungi to aid in production of fresh food out in space and degradation of biological waste; or maybe fungi will be used in the absorption of radiation. Until then, our eyes are peeled.

Tristan Wang ’16 is a junior in Kirkland House concentrating in Organismic and Evolutionary Biology.

Works Cited

Cook, Gareth. “Laura Lee News – Orbiting Spacecraft Turns out to Be Food for Aggressive Mold.” Laura Lee News – Orbiting Spacecraft Turns out to Be Food for Aggressive Mold. Conversation for Exploration, 1 Oct. 2000. Web. Pitt, John I. “Biology and Ecology of Toxigenic Penicillium Species.” Mycotoxins and Food Safety 504 (2002): 29-41. Wilson, David M., Wellington Mubatanhema, and Zelijko Jurjevic. “Biology and Ecology of Mycotoxigenic Aspergillus Species as Related to Economic and Health Concerns.” Mycotoxins and Food Safety 504 (2002): 3-17. Trail, Frances. “Fungal Cannons: Explosive Spore Discharge in the Ascomycota.” FEMS Microbiology Letters 276.1 (2007): 12-18. Moore, David, and Alvidas Stočkus. “Comparing Plant and Fungal Gravitropism Using Imitational Models Based on Reiterative Computation.” Advances in Space Research 21.8-9 (1998): 1179-182. Kher, Kavita, John P. Greening, Jason P. Hatton, Lilyann Novak Frazer, and David Moore. “Kinetics and Mechanics of Stem Gravitropism in Coprinus Cinereus.” Mycological Research 96.10 (1992): 817-24. Melville, Kate. “Chernobyl Fungus Feeds On Radiation.” Chernobyl Fungus Feeds On Radiation. Sci Gogo, 23 May 2007. Web. Dadachova, Ekaterina, and Arturo Casadevall. “Ionizing Radiation: How Fungi Cope, Adapt, and Exploit with the Help of Melanin.” Current Opinion in Microbiology 11.6 (2008): 525-31. Stamets, Paul. Mycelium Running: How Mushrooms Can Help save the World. Berkeley, CA: Ten Speed, 2005. Sánchez, Carmen. “Cultivation of Pleurotus Ostreatus and Other Edible Mushrooms.” Applied Microbiology and Biotechnology 85.5 (2010): 1321-337. Schaechter, Moselio. “Biodeterioration – Including Cultural Heritage.” Encyclopedia of Microbiology. Amsterdam: Elsevier/Academic, 2009. 191-205.