Radiotrophic Fungi: the Art of Survival and Prosperity
Ever imagined life thriving in the aftermath of a nuclear disaster? Join us in the exploration of radiotrophic fungi’s astonishing resilience.
In 1991, remotely piloted robots descended onto the fourth reactor block of the Chornobyl* Nuclear Power Plant.1 This reactor exploded five years before, leading to multiple deaths and the spread of radioactive materials across the European continent. Despite being one of the most radioactive places on Earth, the robots were able to find something quite surprising in the reactor: life. Indeed, black single-celled fungi were flourishing on the reactor walls and rendering the cooling pools black.2 Since the initial mission, scientists have analyzed these fungi and identified 2000 strains originating from 200 different species.3
*Note that the correct transliteration from Ukrainian to English is “Chornobyl”, as opposed to “Chernobyl” (the Russian transliteration) and the former is what will be used throughout this article.
These findings are surprising, as radiation from an exploded nuclear plant is usually not something an organism wants to deal with. In simple terms, radioactivity is energy released from the splitting of nuclei. The energy being thus emitted is called ionizing radiation and it can have disastrous effects on health as the radiation affects the atoms composing our bodies, leading to DNA breaks, mutations, and tissue damage.4
Extraordinarily, some organisms have evolved the capacity to withstand enormous quantities of ionizing radiation, such as some bacteria, tardigrades (fascinating microscopic invertebrates), and, of course, fungi. Fungal spores have been found in the early Cretaceous period deposits, during which the Earth might have been subject to more radiation from space; this time also coincides with the extinction of many plants and animals.2 Nowadays, the Earth’s magnetic field diverts the radiation from space to the poles, protecting us from those harmful rays. But what do we find at high altitudes of the Arctic and Antarctic regions? That’s right, more fungi - even in the windy, cold, and radiation-filled desert of the Antarctic continent.5 One might think that the Chornobyl, Cretaceous, and Antarctic fungi are vastly different, and yet they all have something in common: melanin. The melanin pigment gives the fungi their black color and is helpful when coping with radiation. The melanin pigment in fungi is similar to the melanin molecules that color our skin, eyes, and hair, and offers us a degree of protection against harmful UV rays.6
In fungi, it has been found that melanin is arranged in concentric layers on their cell walls.7 This spatial arrangement, its chemical composition, and the ability of melanin to act as a buffer against free radicals - dangerous ions, atoms or molecules that can be caused by ionizing radiation - seems to allow this pigment to protect fungi against harmful radiation.8 Melanin makes use of the principle of absorbing the radiation and then dissipating its energy so it doesn’t harm the organism through a variety of mechanisms that are not yet fully studied in fungi.9
However, the fungi from the Chornobyl reactor are not merely extremotolerant; they do not only withstand those conditions, they seem to thrive in them! Their hyphae, the branching filaments that create the mycelium, or body of the fungus, extend towards the source of ionizing radiation, a phenomenon called “radiotropism”. Ekaterina Dadachova and Arturo Casadevall studied the effects of a level of radiation that is 500 times higher than normal on three genetically diverse melanized fungal species: Cladosporium sphaerospermum (one of the species found in Chornobyl's reactor), Wangeliella dermatidis, and Cryptococcus neoformans. Wangiella dermatitidis and Cryptococcus neoformans grew much faster, and Cladosporium sphaerospermum was even able to grow in conditions in which nutrients were scarce.10 Given those results, would it be possible that melanin allows those fungi to use ionizing radiation as a source of energy? This still hypothetical phenomenon is termed “radiosynthesis,” and its workings are not yet fully understood. Another interesting phenomenon is “radiostiumlation,” the germination of spores caused by radiation, which was observed in fungal species from radioactively contaminated places.11
Nevertheless, not all species of fungi found in radioactive areas possess melanin, suggesting the existence of an alternative mechanism that enables their survival in such conditions. Even black fungi use other defenses besides melanin, such as multiple types of energy conservation mechanisms allowing them to survive in harsh environments.12
These findings are intrinsically fascinating, but they might also be useful in various applications. Want to get rid of that inconvenient nuclear waste in your backyard? Let these fungi munch away! Indeed, it has been shown that radiotrophic fungi could be used to detect and clean up radioactive waste sites.13 In the field of medicine, they could protect cancer patients undergoing radiation therapy.13 But their potential doesn’t stop here! These fungi could also accompany astronauts on their missions and might even be used in future Martian structures, serving as protection from outer-space radiation.14
From the Cretaceous until now, passing through nuclear catastrophes and icy desolate slopes, fungi have survived and thrived. Their captivating abilities to withstand harsh conditions make them ideal partners in our quests for cleaning up radioactive places, fighting cancer, and exploring places away from Earth. Yet, there remains many discoveries to be made in this fungal universe, from even more creative applications to the intricacies of their exceptional abilities and behaviors.
Literature cited:
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Dadachova E, Casadevall A. Ionizing radiation: how fungi cope, adapt, and exploit with the help of melanin. Current Opinion in Microbiology [Internet]. 2008 Dec;11(6):525–31. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2677413/
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Bland J, Gribble LA, Hamel MC, Wright JB, Moormann G, Bachand M, et al. Evaluating changes in growth and pigmentation of Cladosporium cladosporioides and Paecilomyces variotii in response to gamma and ultraviolet irradiation. Scientific Reports. 2022 Jul 15;12(1).
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Dadachova E, Bryan RA, Howell RC, Schweitzer AD, Aisen P, Nosanchuk JD, et al. The radioprotective properties of fungal melanin are a function of its chemical composition, stable radical presence and spatial arrangement. Pigment Cell & Melanoma Research. 2007 Dec 21;21(2):192–9.
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Dadachova E, Bryan RA, Huang X, Moadel T, Schweitzer AD, Aisen P, et al. Ionizing Radiation Changes the Electronic Properties of Melanin and Enhances the Growth of Melanized Fungi. Rutherford J, editor. PLoS ONE [Internet]. 2007 May 23;2(5):e457. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1866175/
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Tugay T, Zhdanova NN, Zheltonozhsky V, Sadovnikov L, Dighton J. The influence of ionizing radiation on spore germination and emergent hyphal growth response reactions of microfungi. Mycologia [Internet]. 2006 [cited 2023 Nov 5];98(4):521–7. Available from: https://pubmed.ncbi.nlm.nih.gov/17139845/
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USask researchers training fungi to sense radiation and potentially help clean up nuclear waste [Internet]. News. [cited 2023 Nov 5]. Available from: https://news.usask.ca/articles/research/2020/usask-researchers-training-fungi-to-sense-radiation-and-potentially-help-clean-up-nuclear-waste.php
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🍄 Radiotrophic fungi could serve as radiation shield for travellers to Mars [Internet]. Warp News. 2020 [cited 2023 Nov 5]. Available from: https://www.warpnews.org/space/radiotrophic-fungi-could-serve-as-radiation-shield-for-people-on-mars/
Absolutely refreshing and informative