Hungry? Here’s some Radiation: Radiotrophic Fungi & the Role of Melanin on Radiosynthesis

By Ioanna Maria Arvanitaki, Year 13 Student

Introduction

Thirty-nine years have passed since the Chernobyl Disaster (1986), one of the greatest nuclear disasters in history. The incident caused millions of individuals to be exposed to radiation in Europe, with epidemiological studies finding an increase in the prevalence of certain cancers following the accident[1]. Since the nuclear disaster, scientists have returned to study the now destroyed reactor, where they have discovered fungi growing on walls and pools of radioactive water[2]. This sparked great interest in the scientific community: how did fungi adapt to survive under extreme radiation exposure?

Nuclear Radiation and Its Effect on DNA

Radioactivity is a characteristic of unstable atoms possessing superfluous mass or energy, resulting in the spontaneous disintegration of the nucleus[3]. Radioactive atoms decay by emitting α-particles, β-particles or γ-radiation, which is in the form of an electromagnetic wave. The types of radiation emitted differ in terms of ionising and penetrating abilities[4].

We are constantly exposed to low levels of radiation – this is background radiation, and it consists of both natural sources of radiation (such as radon gas, an alpha-emitter formed by the decay of uranium or cosmic rays from the universe) as well as man-made sources of radiation (such as Positron Emission Tomography, PET which utilises radioactive traces)[5].

However, extreme radiation exposure has several negative consequences, leading to Acute Radiation Syndrome (ACS), a broad term that includes a range of signs and symptoms following exposure to high doses of radiation[6].

Radiation generally causes the release of electrons from atoms or molecules to generate ions, which in turn can break covalent bonds. Radiation primarily harms cells by damaging the deoxyribonucleic acid (DNA), the carrier of genetic information. The effect of radiation on DNA depends on several factors, including ionisation energy, absorbed dose, dosage rate, amongst others. The effect of radiation on DNA can be both direct and indirect. Regarding the former category, radiation directly damages DNA by causing breaks in the DNA within chromosomes. Double-stranded breaks (DSB) is a process that also happens in meiosis, and specifically prophase I, to initiate homologous recombination[7]. When radiation (in the form of a high-energy particle or photon) reaches the DNA strand, it causes the phosphodiester backbone to break, creating DSBs[8]. More commonly, however, radiation causes breaks in DNA by splitting water molecules into free hydrogen and hydroxyl radicals, which can react with nearby DNA to produce Single-Stranded breaks (SSBs)[9]. SSBs can then also convert to DSBs[10]. Indirect mechanisms of causing DNA breaks, however, are more usual[11]. The radiolysis of water described above creates Reactive-Oxygen Species (ROS), which can damage DNA by oxidising bases or creating sites of base loss (abasic sites)[12]. Processing and repairing DSBs can cause mutations, loss of heterozygosity, or chromosome rearrangements, all of which may result into apoptosis or cancer[13].

This renders environments like Chernobyl, where exposure to ionising radiation is high, uninhabitable for organisms.

Radiotrophic Fungi

This was the researchers’ assumption until the discovery of thriving fungi in Chernobyl. The genus of identified species included Penicillium, Cryptococcus, Wangiella, Aspergillus, Cladosporium and Aureobasidium[14].

The majority of the specimens that were collected and analysed had very high concentrations of melanin, suggesting the possibility of the protein playing a role in the survival of these fungi under high-radiation levels[15]. Radiotropism was also evident – fungi tended to grow towards radiation. This observation suggests that fungi possessed a mechanism which enabled them to detect radiation. In addition, fungi seemed to be able to decompose organic substances containing radioisotopes, including graphite[16].

Several years later, scientists identified the same cultures in other high-radiation regions, including space stations [17]. So how do these fungi manage to survive under exposure to such high levels of radiation?

Radiosynthesis and The Role of Melanin

Melanin is an insoluble and stable pigment, formed by the oxidative phosphorylation of phenolic compounds in melanosomes[18]. The pigment is brown or black in colour, and is associated with protection against oxidative or ionising agents, as well as against Ultraviolet (UV) and solar radiation[19].

The radioprotective properties of melanin are due to both physical shielding from ionising radiation, as well as the molecule’s chemical ability to take up cytotoxic radicals (which form by direct ionisation due to radiation or due to the radiolysis of water), thereby preventing damage to DNA and to the cell. This is because melanin already contains stable radicals on its own structure[20].

The structure of melanin is highly complex and has not yet been discovered. Melanin is synthesised in organisms through two distinct synthetic pathways. Fungi use one of the two pathways, where an endogenous substrate (acetyl-CoA or malonyl-CoA) is initially converted to 1,3,6,8-tetrahydroxynaphthalene (1,3,6,8-THN) in a reaction catalysed by polyketide synthase (PKS). This compound is then converted to scytalone, and following dehydration, to 1,3,8-trihydroxynaphthalene (THN). THN is reduced to form vermelone, which undergoes another dehydration reaction to form 1,8-dihydroxynaphthalene (DHN), which can be polymerised to DHN-melanin[21]. The other synthetic pathway would involve L-3,4-dihydroxyphenylalanine (L-DOPA)[22].

Melanised fungi were found to have stronger cell walls with reduced permeability[23]. Other experiments found that radiation increased the electron transfer capacity of ionised melanin of melanised fungi, with radiation significantly increasing the growth of melanised species compared to exposure to background radiation[24]. The latter observation applied even in environments of low nutrient supply, suggesting the possibility of autotrophy via radiosynthesis.  In particular, XTT (2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-5-[(phenylamino) carbonyl]-2H-tetrazolium hydroxide) and MTT (2-(4,5-dimethyl-2-thiazolyl)-3,5-diphenyl-2H-tetrazolium bromide) assays suggested greater metabolism in melanised cells compared to non-melanised cells[25].

Currently, the hypothesis is that melanin provides fungi with the ability to sense and somehow harness the energy transferred by ionising radiation, similarly to photosynthetic pigments, which harness energy from sunlight[24].

The Future of Radiotrophic Fungi

The applications of radiotrophic fungi in the near future could be several.

One suggested application involves the use of radiotrophic fungi as biological sensors. The ability of these species to detect radiation in the environment, as well as the radiotropism that they exhibit makes them useful for detecting and measuring radiation levels[26].

Furthermore, given the ability of these fungi to absorb radioisotopes from their environment, such as radioactive isotopes of uranium and radon, they could be used to remove radioisotopes from the soil, thereby acting as bioremediation agents[27]. Alternatively, they could even be used in bioleaching, by being applied to minerals and rocks to leach, for instance, uranium[28].

Note that radiotrophic fungi were also found in space stations, such as MIR or ISS, in zero-gravity environments[15]. Researchers suggest that these fungi can be used as radioprotective agents to create fibres, for the fabrication of radioprotective clothing for space travel, amongst other uses. The lightweight nature of the fungi (compared, for instance, to steel) as well as their ability to regenerate through self-replication makes them very useful for such applications[17].

Other studies focus instead on the use of fungal melanin in cancer research and medical applications, including the protection of healthy organs from high doses of radiation in patients undergoing radiotherapy[29].

Concluding Remarks

The future of radiotrophic fungi remains very promising, with applications ranging from space travel to radiotherapy. Nevertheless, the current mechanism by which fungi use melanin for radiosynthesis remains poorly understood and rests mainly on hypotheses. Before using radiotrophic fungi, we have to first establish the structure of melanin and understand how it provides fungi with the necessary nutrients for survival. That being said, research on the topic is still very recent and is currently being continued to better comprehend this new mechanism of autotrophy.

Bibliography

[1] Cardis, E., and M. Hatch. “The Chernobyl Accident — an Epidemiological Perspective.” Clinical Oncology (Royal College of Radiologists (Great Britain)), vol. 23, no. 4, May 2011, pp. 251–60. PubMed Central, https://doi.org/10.1016/j.clon.2011.01.510.

[2] Ireland, Tom. “Eating Gamma Radiation for Breakfast.” The Biologist, Sep. 2025, https://www.rsb.org.uk//biologist-features/eating-gamma-radiation-for-breakfast.

[3] Murray, Raymond L. “Chapter 3 - Radioactivity.” Nuclear Energy (Sixth Edition), edited by Raymond L. Murray, Butterworth-Heinemann, 2009, pp. 29–40. ScienceDirect, https://doi.org/10.1016/B978-0-12-370547-1.00003-1.

[4] Kahan, R. S., et al. “Comparison of the Effect of Radiation of Various Penetrating Powers on the Damage to Citrus Fruit Peel.” Radiation Botany, vol. 8, no. 5, Jan. 1968, pp. 415–23. ScienceDirect, https://doi.org/10.1016/S0033-7560(68)80042-0.

[5] Ojovan, Michael I., et al. “Chapter 5 - Background Radiation.” An Introduction to Nuclear Waste Immobilisation (Third Edition), edited by Michael I. Ojovan et al., Elsevier, 2019, pp. 47–55. ScienceDirect, https://doi.org/10.1016/B978-0-08-102702-8.00005-4.

[6] Acosta, Robert, and Steven J. Warrington. “Radiation Syndrome.” StatPearls, StatPearls Publishing, 2023. PubMed, http://www.ncbi.nlm.nih.gov/books/NBK441931/.

[7] Murakami, Hajime, and Scott Keeney. “Regulating the Formation of DNA Double-Strand Breaks in Meiosis.” Genes & Development, vol. 22, no. 3, Feb. 2008, pp. 286–92. PubMed Central, https://doi.org/10.1101/gad.1642308.

[8] Cannan, Wendy J., and David S. Pederson. “Mechanisms and Consequences of Double-Strand DNA Break Formation in Chromatin.” Journal of Cellular Physiology, vol. 231, no. 1, Jan. 2016, pp. 3–14. PubMed Central, https://doi.org/10.1002/jcp.25048.

[9] Barnard, Stephen, et al. “The Shape of the Radiation Dose Response for DNA Double-Strand Break Induction and Repair.” Genome Integrity, vol. 4, no. 1, Mar. 2013, p. 1. PubMed, https://doi.org/10.1186/2041-9414-4-1.

[10] Polyzos, Aris A., et al. “Base Excision Repair and Double Strand Break Repair Cooperate to Modulate the Formation of Unrepaired Double Strand Breaks in Mouse Brain.” Nature Communications, vol. 15, no. 1, Sep. 2024, p. 7726. www.nature.com, https://doi.org/10.1038/s41467-024-51906-5.

[11] Talapko, Jasminka, et al. “Health Effects of Ionizing Radiation on the Human Body.” Medicina, vol. 60, no. 4, Apr. 2024, p. 653. PubMed Central, https://doi.org/10.3390/medicina60040653.

[12] Borrego-Soto, Gissela, et al. “Ionizing Radiation-Induced DNA Injury and Damage Detection in patients with Breast Cancer.” Genetics and Molecular Biology, vol. 38, no. 4, 2015, pp. 420–32. PubMed Central, https://doi.org/10.1590/S1415-475738420150019.

[13] Ceccaldi, Raphael, et al. “Repair Pathway Choices and Consequences at the Double-Strand Break.” Trends in Cell Biology, vol. 26, no. 1, Jan. 2016, pp. 52–64. DOI.org (Crossref), https://doi.org/10.1016/j.tcb.2015.07.009.

[14] Zhdanova, Nelli N., Valentina A. Zakharchenko, et al. “Fungi from Chernobyl: Mycobiota of the Inner Regions of the Containment Structures of the Damaged Nuclear Reactor.” Mycological Research, vol. 104, no. 12, Dec. 2000, pp. 1421–26. DOI.org (Crossref), https://doi.org/10.1017/S0953756200002756.

[15] Dadachova, Ekaterina, Ruth A. Bryan, Robertha C. Howell, 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, vol. 21, no. 2, Apr. 2008, pp. 192–99. PubMed, https://doi.org/10.1111/j.1755-148X.2007.00430.x.

[16] Zhdanova, Nelli N., Tatyana Tugay, et al. “Ionizing Radiation Attracts Soil Fungi.” Mycological Research, vol. 108, no. 9, Sep. 2004, pp. 1089–96. ScienceDirect, https://doi.org/10.1017/S0953756204000966.

[17] Shunk, Graham K., et al. “Growth of the Radiotrophic Fungus Cladosporium Sphaerospermum Aboard the International Space Station and Effects of Ionizing Radiation.” 17 Jul. 2020. Microbiology, https://doi.org/10.1101/2020.07.16.205534.

[18] Guo, Lili, et al. “Recent Advances and Progress on Melanin: From Source to Application.” International Journal of Molecular Sciences, vol. 24, no. 5, Feb. 2023, p. 4360. PubMed Central, https://doi.org/10.3390/ijms24054360.

[19] Brenner, Michaela, and Vincent J. Hearing. “The Protective Role of Melanin Against UV Damage in Human Skin.” Photochemistry and Photobiology, vol. 84, no. 3, 2008, pp. 539–49. PubMed Central, https://doi.org/10.1111/j.1751-1097.2007.00226.x.

[20] Herrling, Thomas, et al. “The Role of Melanin as Protector against Free Radicals in Skin and Its Role as Free Radical Indicator in Hair.” Spectrochimica Acta. Part A, Molecular and Biomolecular Spectroscopy, vol. 69, no. 5, May 2008, pp. 1429–35. PubMed, https://doi.org/10.1016/j.saa.2007.09.030.

[21] Eisenman, Helene C., and Arturo Casadevall. “Synthesis and Assembly of Fungal Melanin.” Applied Microbiology and Biotechnology, vol. 93, no. 3, Feb. 2012, pp. 931–40. PubMed, https://doi.org/10.1007/s00253-011-3777-2.

[22] Hearing, Vincent J. “Determination of Melanin Synthetic Pathways.” Journal of Investigative Dermatology, vol. 131, Nov. 2011, pp. E8–11. ScienceDirect, https://doi.org/10.1038/skinbio.2011.4.

[23] Jacobson, Eric S., and Reiko Ikeda. “Effect of Melanization upon Porosity of the Cryptococcal Cell Wall.” Medical Mycology, vol. 43, no. 4, Jan. 2005, pp. 327–33. DOI.org (Crossref), https://doi.org/10.1080/13693780412331271081.

[24] Tibolla, Matheus Henrique, and Janaína Fischer. “Radiotrophic Fungi and Their Use as Bioremediation Agents of Areas Affected by Radiation and as Protective Agents.” Research, Society and Development, vol. 14, no. 1, Jan. 2025, p. e2514147965. DOI.org (Crossref), https://doi.org/10.33448/rsd-v14i1.47965.

[25] Dadachova, Ekaterina, Ruth A. Bryan, Xianchun Huang, et al. “Ionizing Radiation Changes the Electronic Properties of Melanin and Enhances the Growth of Melanized Fungi.” PLoS ONE, edited by Julian Rutherford, vol. 2, no. 5, May 2007, p. e457. DOI.org (Crossref), https://doi.org/10.1371/journal.pone.0000457.

[26] Malo, Mackenzie E., et al. “Radioadapted Wangiella Dermatitidis Senses Radiation in Its Environment in a Melanin-Dependent Fashion.” Fungal Biology, vol. 124, no. 5, May 2020, pp. 368–75. DOI.org (Crossref), https://doi.org/10.1016/j.funbio.2019.10.011.

[27] Jørgensen, Kirsten S. “In Situ Bioremediation.” Advances in Applied Microbiology, vol. 61, Elsevier, 2007, pp. 285–305. DOI.org (Crossref), https://doi.org/10.1016/S0065-2164(06)61008-3.

[28] Saldaña, Manuel, et al. “Bioleaching Modeling—A Review.” Materials, vol. 16, no. 10, May 2023, p. 3812. DOI.org (Crossref), https://doi.org/10.3390/ma16103812.

[29] Schweitzer, Andrew D., et al. “MELANIN-COVERED NANOPARTICLES FOR PROTECTION OF BONE MARROW DURING RADIATION THERAPY OF CANCER.” International Journal of Radiation Oncology, Biology, Physics, vol. 78, no. 5, Dec. 2010, pp. 1494–502. PubMed Central, https://doi.org/10.1016/j.ijrobp.2010.02.020.