Radiotrophic fungus

Short description: Fungus capable of radiosynthesis

Cryptococcus neoformans stained with light India ink

Radiotrophic fungi are fungi that can perform the biological process called radiosynthesis, which means using ionizing radiation as a main energy source to drive metabolization. It has been claimed that radiotrophic fungi have been found in extreme environments such as in the Chernobyl Nuclear Power Plant.[1][2]

Most radiotrophic fungi use melanin in some capacity to survive.[3] The process of using radiation and melanin for energy has been termed radiosynthesis, and is thought to be analogous to anaerobic respiration.[4] However, it is not known if multi-step processes such as photosynthesis or chemosynthesis are used in radiosynthesis.

## Contents

* 1 Discovery
* 2 Role of melanin
* 3 Comparisons with non-melanized fungi
* 4 Use in human spaceflight
* 5 See also
* 6 References
* 7 External links

## Discovery

Many fungi have been isolated from the area around the destroyed Chernobyl Nuclear Power Plant, some of which have been observed directing their growth of hyphae toward radioactive graphite from the disaster, a phenomenon called “radiotropism”.[5][1] Study has ruled out the presence of carbon as the resource attracting the fungal colonies, and in fact concluded that some fungi will preferentially grow in the direction of the source of beta and gamma ionizing radiation, but were not able to identify the biological mechanism behind this effect.[1] It has also been observed that other melanin-rich fungi were discovered in the cooling water from some other working nuclear reactors. The light-absorbing compound in the fungus cell membranes had the effect of turning the water black.[6] While there are many cases of extremophiles (organisms that can live in severe conditions such as that of the radioactive power plant), a hypothetical radiotrophic fungus would grow because of the radiation, rather than in spite of it.[7]

Further research conducted at the Albert Einstein College of Medicine showed that three melanin-containing fungi—Cladosporium sphaerospermum, Wangiella dermatitidis, and Cryptococcus neoformans—increased in biomass and accumulated acetate faster in an environment in which the radiation level was 500 times higher than in the normal environment. C. sphaerospermum in particular was chosen due to this species being found in the reactor at Chernobyl. Dadachova et al found that by exposing C. neoformans cells to these radiation levels, the organisms rapidly (within 20–40 minutes of exposure) altered the chemical properties of their melanin, and increased melanin-mediated rates of electron transfer (measured as reduction of ferricyanide by NADH) three- to four-fold compared with unexposed organisms. However, each culture was performed with at least limited nutrients provided to each fungus. The increase in biomass and other effects could be caused either by the cells directly deriving energy from ionizing radiation, or by the radiation allowing the cells to utilize traditional nutrients either more efficiently or more rapidly.[7]

Outside of the laboratory studies, similar effects on melanin electron-transport capability were observed by the authors after organism exposure to non-ionizing radiation. The authors did not conclude whether light or heat radiation would have a similar effect on the fungi.[7]

## Role of melanin

Melanins are a family of dark-colored, naturally occurring pigments with radiation-shielding properties. These pigments can absorb electromagnetic radiation due to their molecular structure, which results in their dark color; this quality suggests that melanin could help protect radiotropic fungi from ionizing radiation. It has been suggested that melanin's radiation-shielding properties are due to its ability to trap free radicals formed during radiolysis of water.[8] Melanin production is also advantageous to the fungus in that it can aid survival in many extreme environments. Examples of these environments include the Chernobyl Nuclear Power Plant,[2] the International Space Station,[4] and the Transantarctic Mountains.[9] Melanin may also be able to help the fungus metabolize radiation, but more evidence and research is still needed.[3]

## Comparisons with non-melanized fungi

Melanization may come at some metabolic cost to the fungal cells. In the absence of radiation, some non-melanized fungi (that had been mutated in the melanin pathway) grew faster than their melanized counterparts. Limited uptake of nutrients due to the melanin molecules in the fungal cell wall or toxic intermediates formed in melanin biosynthesis have been suggested to contribute to this phenomenon.[7] It is consistent with the observation that despite being capable of producing melanin, many fungi do not synthesize melanin constitutively (i.e., all the time), but often only in response to external stimuli or at different stages of their development.[10] The exact biochemical processes in the suggested melanin-based synthesis of organic compounds or other metabolites for fungal growth, including the chemical intermediates (such as native electron donor and acceptor molecules) in the fungal cell and the location and chemical products of this process, are unknown.[citation needed] Radiotrophic fungi are speculated to have been more widespread and numerous in the Hadean with Natural nuclear fission reactor phenomena being more abundant. The pathway to radio-synthesis may exist dormant, as a sort genetic appendix in several other ancient lifeforms.[citation needed]

## Use in human spaceflight

It is hypothesized that radiotrophic fungi could potentially be used as a shield to protect against radiation,[4] specifically in relation to the use of astronauts in space or other atmospheres. An experiment taking place at the International Space Station in December 2018 through January 2019 was conducted in order to test whether radiotrophic fungi could provide protection from ionizing radiation in space, as part of research efforts preceding a possible trip to Mars. This experiment used the radiotrophic strain of the fungus Cladosporium sphaerospermum.[4] The growth of this fungus and its ability to deflect the effects of ionizing radiation were studied for 30 days aboard the International Space Station. This experimental trial yielded very promising results.

The amount of radiation deflected was found to directly correlate with the amount of fungus. There was no difference in the reduction of ionizing radiation between the experimental and control group within the first 24 hour period; however, once the fungus had reached an adequate maturation, and with a 180° protection radius, amounts of ionizing radiation were significantly reduced as compared to the control group. With a 1.7 mm thick shield of melanized radiotrophic Cladosporium sphaerospermum, measurements of radiation nearing the end of the experimental trial were found to be 2.42% lower, demonstrating radiation deflecting capabilities five times that of the control group. Under circumstances in which the fungi would fully encompass an entity, radiation levels would be reduced by an estimated 4.34±0.7%.[4] Estimations indicate that approximately a 21 cm thick layer could significantly deflect the annual amount of radiation received on Mars’ surface. Limitations to the use of a radiotrophic fungi based shield include increased mass on missions. However as a viable substitute to reduce overall mass on potential Mars missions, a mixture with equal mole concentration of Martian soil, melanin, and a layer of fungi roughly 9 cm thick, could be used.[4]

## See also

* Chernobyl disaster § Flora, fauna, and funga
* Radioresistance, the ability of an organism to withstand ionizing radiation
* Extremophile, an organism able to live in an extreme environment
* Nylon-eating bacteria
* Plastivore
* Project Hail Mary - a sci-fi novel where a fictional astrophage feeds on electromagnetic radiation

## References

1. ↑ 1.0 1.1 1.2 Zhdanova, Nelli N.; Tugay, Tatyana; Dighton, John; Zheltonozhsky, Victor; McDermott, Patrick (September 2004). "Ionizing radiation attracts soil fungi". Mycological Research 108 (Pt 9): pp. 1089–1096. doi:10.1017/s0953756204000966. ISSN 0953-7562. PMID 15506020.
2. ↑ 2.0 2.1 Vember, V. V., and N. N. Zhdanova. "Peculiarities of linear growth of the melanin-containing fungi Cladosporium sphaerospermum Penz. and Alternaria alternata (Fr.) Keissler." Mikrobiolohichnyi Zhurnal (Kiev, Ukraine: 1993) 63.3 (2001): 3-12.
3. ↑ 3.0 3.1 Dadachova, Ekaterina; Casadevall, Arturo (December 2008). "Ionizing Radiation: how fungi cope, adapt, and exploit with the help of melanin". Current Opinion in Microbiology 11 (6): 525–531. doi:10.1016/j.mib.2008.09.013. ISSN 1369-5274. PMID 18848901.
4. ↑ 4.0 4.1 4.2 4.3 4.4 4.5 Shunk, Graham K.; Gomez, Xavier R.; Averesch, Nils J. H. (2020-07-17). "A Self-Replicating Radiation-Shield for Human Deep-Space Exploration: Radiotrophic Fungi can Attenuate Ionizing Radiation aboard the International Space Station". bioRxiv 10.1101/2020.07.16.205534.
5. ↑ Bland, J.; Gribble, L. A.; Hamel, M. C.; Wright, J. B.; Moormann, G.; Bachand, M.; Wright, G.; Bachand, G. D. (2022). "Evaluating changes in growth and pigmentation of Cladosporium cladosporioides and Paecilomyces variotii in response to gamma and ultraviolet irradiation". Scientific Reports 12 (1): 12142. doi:10.1038/s41598-022-16063-z. PMID 35840596. Bibcode: 2022NatSR..1212142B.
6. ↑ Castelvecchi, Davide (May 26, 2007). "Dark Power: Pigment seems to put radiation to good use". Science News 171 (21): 325. Archived from the original on 2008-04-24. https://web.archive.org/web/20080424001002/http://www.sciencenews.org/articles/20070526/fob5.asp.
7. ↑ 7.0 7.1 7.2 7.3 Rutherford, Julian, ed (2007). "Ionizing radiation changes the electronic properties of melanin and enhances the growth of melanized fungi". PLOS ONE 2 (5): e457. doi:10.1371/journal.pone.0000457. PMID 17520016. Bibcode: 2007PLoSO...2..457D.
8. ↑ Gessler, N. N.; Egorova, A. S.; Belozerskaya, T. A. (2014). "Melanin pigments of fungi under extreme environmental conditions (Review)" (in en). Applied Biochemistry and Microbiology 50 (2): 105–113. doi:10.1134/S0003683814020094. ISSN 0003-6838. PMID 25272728.
9. ↑ Balter, Michael (23 May 2007). "Zapped By Radiation, Fungi Flourish" (in en). https://www.science.org/content/article/zapped-radiation-fungi-flourish.
10. ↑ "Relationship between secondary metabolism and fungal development". Microbiol Mol Biol Rev 66 (3): 447–459. 2002. doi:10.1128/MMBR.66.3.447-459.2002. PMID 12208999.

## External links

* Einstein College of Medicine on radiotrophic fungi
* The blacker the better… especially in Chernobyl at Earthling Nature.

[1] "This black fungus might be healing chernobyl by "drinking radiation" a biologist explains.

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Metabolism, catabolism, anabolism

General|

* Metabolic pathway
* Metabolic network
* Primary nutritional groups

Energy
metabolism|

| Aerobic respiration|

* Glycolysis → Pyruvate decarboxylation → Citric acid cycle → Oxidative phosphorylation (electron transport chain \+ ATP synthase)

|

Anaerobic respiration|

* Electron acceptors are other than oxygen

Fermentation|

* Glycolysis → Substrate-level phosphorylation
* ABE
* Ethanol
* Lactic acid

Specific
paths|

| Protein metabolism|

* Protein synthesis
* Catabolism

|

Carbohydrate metabolism
(carbohydrate catabolism
and anabolism)|

| Human|

* Glycolysis ⇄ Gluconeogenesis

* Glycogenolysis ⇄ Glycogenesis

* Pentose phosphate pathway
* Fructolysis
* Galactolysis

* Glycosylation
* N-linked
* O-linked

Nonhuman|

* Photosynthesis
* Anoxygenic photosynthesis
* Chemosynthesis
* Carbon fixation

* Xylose metabolism
* Radiotrophism

Lipid metabolism
(lipolysis, lipogenesis)|

| Fatty acid metabolism|

* Fatty acid degradation (Beta oxidation)
* Fatty acid synthesis

|

Other|

* Steroid metabolism
* Sphingolipid metabolism
* Eicosanoid metabolism
* Ketosis
* Reverse cholesterol transport

Amino acid|

* Amino acid synthesis
* Urea cycle

Nucleotide
metabolism|

* Purine metabolism
* Nucleotide salvage
* Pyrimidine metabolism

Other|

* Metal metabolism
* Iron metabolism
* Ethanol metabolism

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