The explosion of the Chernobyl Nuclear Power Plant in 1986 remains one of the worst and most talked about nuclear plant disasters to date and is still one of the most radioactive places in the world. But surprisingly, the high content of leftover radiation is not preventing all life from growing and even thriving. At least three fungal species have been found at Chernobyl which show enhanced growth rates because of their radioactive environments. Due to properties inherent within these fungi, they may not only provide a great mycoremediation technique for cleaning radiation but could also lead to a self-replicating fungal sunscreen for astronauts living on Mars. (1)
Some melanized fungi found in Chernobyl thrive in radioactive environments
As of the year 2000, around 2000 fungal strains representing 200 species across 98 genera were found in and around the Chernobyl Nuclear Power Plant. (2) Research completed in 2007 at the Albert Einstein College of Medicine has shown that at least three of the fungal species found, Cladosporium sphaerospermum, Wangiella dermatitidis and Cryptococcus neoformans display enhanced growth rates in response to ionizing radiation. (3) This may be due to the fungi’s melanin.
Image credits: Matt Bertone
Melanin is known best for providing our skin’s pigmentation. The melanin in our skin absorbs UV energy and converts it into heat energy, thereby protecting more sensitive molecules such as proteins and DNA. (4) Fungal melanin also absorbs UV energy and converts it into heat and similarly to that of a plant’s chlorophyll, which takes in sunlight and converts it to chemical energy (photosynthesis), fungal melanin appears to take in ionizing gamma radiation and convert it to chemical energy. (1)
The authors of the research completed in 2007 cautiously theorize that “the ability of [the fungi’s] melanin to capture electromagnetic radiation combined with [melanin’s] remarkable oxidation-reduction properties may confer upon melanotic organisms the ability to harness radiation for metabolic energy”. And that “additional investigation [is needed] to ascertain the mechanism for this effect.” (3)
A self-replicating fungal sunscreen
Survival outside of the protection of our planet’s magnetic shield and atmosphere is contingent upon an effective radiation shield. For reference, radiation experienced on Earth is ~.62 rads per year, radiation experienced on the ISS is ~8 rads per year, which is ~13 times higher than on Earth, and the Mars Odyssey Probe found levels of radiation on Mars to be 2.5 times higher than on the ISS, or ~32 times higher than those found on Earth. (5)
Another limiting factor of space exploration is reducing the up-mass of spacecraft. In-Situ Resource Utilization (ISRU) is a set of practices for breaking the supply chain from Earth and using materials harvested or manufactured in situ on other astronomical objects. As fungi are self-replicating, they can be used as an ISRU solution to grow radiation shielding, therefore limiting the up-mass of any spacecraft taking part in a mission employing this solution. (1)
In 2018, researchers sent an experiment aboard the International Space Station (ISS) to test one of these fungus’s, Cladosporium sphaerospermum, ability to grow and shield cosmic radiation. The scientists used a split petri-dish, one side with a combination of the fungus and agar (experiment) and the other side with only agar (control), and placed radiation sensors on either side of the Petri dish. They found that “[at] full maturity, radiation beneath a ≈ 1.7 mm thick lawn of the melanized radiotrophic fungus [] was 2.17±0.35% lower as compared to the negative control.” They estimate that “a ~ 21 cm thick layer of this fungus could largely negate the annual dose-equivalent of the radiation environment on the surface of Mars.” The researchers also found that while usually this fungus takes 14 days for sufficient growth to occur, “in the on-orbit lab, Cladosporium sphaerospermum reached maximum growth rate after approximately 18 hours, and full maturity after 48 hrs.” This solution proves compatible with ISRU principles and could prove invaluable for up-mass savings. (1)
Then, in 2019, researchers at the John Hopkins Bloomberg School of Public Health sent another of the fungi, Cryptococcus neoformans, aboard the ISS to evaluate the protective effects of melanin. The scientists grew both melanized and non-melanized clones of Cryptococcus neoformans lawns on agar, put them in a parylene coated silicone tube and had them placed aboard the Japanese Experimental Module, KIBO. They found that the melanized clones had a 50% higher viability that that of those non-melanized. Included with the experiment were a melanin-coated and an uncoated dosimeter, but no useful data could be obtained from either of these cards. (6)
These experiments show that melanized fungi have the potential to protect astronauts from cosmic radiation and can limit the up-mass of the space-crafts whose mission employs them. More research will need to be completed to further understand how fungi interact with radiation and what role melanin plays in this interaction.
Fungal solutions may lead to further understandings
Another exciting thing about this research is that we have always seen ionizing radiation as a destructive force, but this allows us to see it differently, which could lead to other solutions for ionizing radiation in the future. When fear does not paint one's thoughts, new pathways are found.
References:
Shunk, G.K., Gomez, X.R., & Averesch, N.J. A Self-Replicating Radiation-Shield for Human Deep-Space Exploration: Radiotrophic Fungi can Attenuate Ionizing Radiation aboard the International Space Station. bioRxiv 2020.07.16.205534; doi:10.1101/2020.07.16.205534
ZHDANOVA NN, ZAKHARCHENKO VA, VEMBER VV, NAKONECHNAYA LT. Fungi from Chernobyl: mycobiota of the inner regions of the containment structures of the damaged nuclear reactor. Mycological Research. 2000;104(12):1421-1426. doi:10.1017/S0953756200002756
Dadachova E, Bryan RA, Huang X, Moadel T, Schweitzer AD, Aisen P, Nosanchuk JD, Casadevall A. Ionizing radiation changes the electronic properties of melanin and enhances the growth of melanized fungi. PLoS One. 2007 May 23;2(5):e457. doi: 10.1371/journal.pone.0000457. PMID: 17520016; PMCID: PMC1866175.
Ilina A, Thorn KE, Hume PA, Wagner I, Tamming RR, Sutton JJ, Gordon KC, Andreassend SK, Chen K, Hodgkiss JM. The photoprotection mechanism in the black-brown pigment eumelanin. Proc Natl Acad Sci U S A. 2022 Oct 25;119(43):e2212343119. doi: 10.1073/pnas.2212343119. Epub 2022 Oct 13. PMID: 36227945; PMCID: PMC9618045.
Williams, Matt. “How bad is the radiation on Mars?” Phys.Org, 16 Nov. 2021, phys.org/news/2016-11-bad-mars.html#:~:text=Over%20the%20course%20of%20about,(8%20rads)%20per%20year?
Cordero, R.J.B., Dragotakes, Q., Friello, P.J. and Casadevall, A. (2022), Melanin protects Cryptococcus neoformans from spaceflight effects. Environmental Microbiology Reports, 14: 679-685. doi:10.1111/1758-2229.13078
Contributing Author: April Kissinger
April is a fungi fanatic that has held a number of diverse STEM positions over the past 12 years. She is currently devoting her time to studying our fungal friends, as she feels the future begins with "Myco" !
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