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radiotrophic fungi

Of the 6 kingdoms in the domain of the Eukaryotes, fungi may be one of the least studied of all.

 

The title of the largest organism in the world belongs to a form of fungi. Fungi are the reason terrestrial animals and land plants are even able to exist (1). From bioluminescent hyphae to hallucination-inducing psilocybin mushrooms, fungi are far from uninteresting. And perhaps the most noteworthy of this fascinating kingdom is that of radiotrophic fungi.

Radiotrophic fungi are a type of fungi that appear to use radiosynthesis to survive. Melanin contained in the fungi converts gamma radiation (a form of electromagnetic, indirectly ionizing radiation formed by the decay of atomic nuclei) into chemical energy to support their growth; this process is analogous to photosynthesis. (2) They were first discovered after the Chernobyl incident, after a black fungus had colonized the walls of the damaged reactor 4, and in the reactor’s largely radioactive cooling pool water. 

To give an idea of how radioactive that is, here are some examples: Chernobyl’s suicide squad - three men who volunteered to swim through heavily radioactive water to drain millions of gallons underneath a molten reactor core - came out immediately displaying symptoms of acute radiation syndrome, despite having only been inside for a short period of time. (3) In 2005, it was estimated that of the 60,000 citizens of Chernobyl - mostly involved in recovery and cleanup work - who were exposed to high doses of radiation, 4000 would eventually die from cancer. Another study from the same year showed that almost 20 years after the incident, one of the most affected regions in Ukraine still appeared to have a higher rate of birth defects (4). 

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Under normal conditions, any creature living as near to Chernobyl as the radiotrophic fungi currently live would suffer severely from radiation poisoning before an agonizingly painful death. Ionizing radiation released from atoms in the form of electromagnetic waves or particles have the ability to completely remove electrons from other atoms and molecules. (5) They can weaken up or even break DNA altogether, either damaging cells until they are killed or causing them to mutate.(6)

For humans, this can mean two things: direct tissue damage and cancer. Not to mention radiation burns, poisoning, cardiovascular disease, Acute Radiation Syndrome, Cutaneous Radiation Injuries, etc. So, a radiotrophic fungus’ ability to thrive in environments with a radiation dose approximately 3 to 5 orders of magnitude higher than normal background radioactivity naturally interested many scientists. 

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Figure 3: Radiotrophic fungi growing on the Mir orbital space station

Not only have they been found in Chernobyl, but also throughout other highly radioactive regions including the Arctic and Antarctic, as well as high altitude areas, and interestingly - orbiting spacecraft. The Russian orbital station Mir and the International Space Station needed/needs to be continually cleaned due to fungal growth, as some fungi have the potential to be human pathogens and even degrade structural materials within the aircraft. A survey of the environmental contamination aboard the ISS revealed that the high levels of ionizing radiation were not in the least fungicidal, rather they were thriving in their harsh environment. Another electron-microscopy investigation in which two species of the fungi were subjected to the extreme open space conditions outside of the aircraft for 7 months (called the “Biorisk” experiment) showed that Aspergillus Versicolor and Penicillium expansum went through morphological changes; “For example, the polysaccharide capsule and melanin layer in P. expansum were significantly increased in comparison with control samples, as well the numbers of mitochondria and vacuoles in space-exposed fungi were much higher than in controls.” From a microbiological perspective, this could provide danger in the sense that a species of fungi may change so drastically during its time in space that it could pose a threat for Earth’s inhabitants.

Any radiation emitted by our sun is mainly composed of non-ionizing radiation, though it is still present in small amounts. Some planets produce even more ionizing radiation than the sun. If such a fungi that thrives off ionizing radiation from some of the most radioactive places on Earth can exist, what could this mean for life on those other planets?

Bibliography

(1) Chris, D. (2018). Fungi Are Responsible For Life On Land As We Know It. Retrieved from CBC: https://www.cbc.ca/natureofthings/features/fungi-are-responsible-for-life-on-land-as-we-know-it

(2) Wikipedia. (2020, November 24). Radiotrophic Fungus. Retrieved from Wikipedia the Free Encyclopedia: https://en.wikipedia.org/wiki/Radiotrophic_fungus

(3) Tahir, T. (2019, June 14). NUKE HERO Chernobyl ‘suicide squad’ diver tells how he averted a second apocalyptic blast that would have devastated Europe . Retrieved from The Sun: https://www.thesun.co.uk/news/9298446/chernobyl-diver-averted-second-blast-devastated-europe/#:~:text=A%20CHERNOBYL%20engineer%20has%20recalled,from%20underneath%20the%20burning%20reactor.

(4) Norton, A. (2010, March 25). Higher birth-defect rate seen in Chernobyl area. Retrieved from Reuters Health: https://www.reuters.com/article/us-defect-chernobyl/higher-birth-defect-rate-seen-in-chernobyl-area-idUSTRE62N4L820100324

(5) CDC (Centers for Disease Control and Prevention). (2015, December 7). Ionizing Radiation. Retrieved from CDC (Centers for Disease Control and Prevention): https://www.cdc.gov/nceh/radiation/ionizing_radiation.html#:~:text=Ionizing%20radiation%20is%20a%20form%20of%20energy%20that%20acts%20by,and%20pass%20through%20these%20materials.

(6) Ashford, M. (2011, March 16). FYI: How Does Nuclear Radiation Do Its Damage? Retrieved from Popular Science: https://www.popsci.com/science/article/2011-03/fyi-how-does-nuclear-radiation-do-its-damage/

Dadachova, E., & Casadevall, A. (2008, October 24). Ionizing Radiation: how fungi cope, adapt, and exploit with the help of melanin. Retrieved from National Center for Biotechnology Information: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2677413/

By Sarisa Techasukij

(Year 10 Student at Bangkok Patana School)