Cryptococcus neoformans using a light India ink staining preparation PHIL 3771 lores

Radiotrophic fungi are

fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately fr ...

that can use

radiation In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium. This includes: * ''electromagnetic radiation'', such as radio waves, microwaves, infrared, visi ...

as an energy source to stimulate growth. Radiotrophic fungi have been found in extreme environments such as in the

Chernobyl Nuclear Power Plant The Chernobyl Nuclear Power Plant (ChNPP; ; ), is a nuclear power plant undergoing decommissioning. ChNPP is located near the abandoned city of Pripyat in northern Ukraine northwest of the city of Chernobyl, from the Belarus–Ukraine borde ...

. Most known radiotrophic fungi utilize

melanin Melanin (; from el, μέλας, melas, black, dark) is a broad term for a group of natural pigments found in most organisms. Eumelanin is produced through a multistage chemical process known as melanogenesis, where the oxidation of the amino ...

in some capacity to survive. The process of using radiation and melanin for energy has been termed

radiosynthesis Radiosynthesis is a fully automated synthesis method in which radioactive compounds are produced. Radiosynthesis is generally carried out by several nuclear interface modules, which are protected by the lead shielding and controlled by a comp ...

, and is thought to be analogous to

anaerobic respiration Anaerobic respiration is respiration using electron acceptors other than molecular oxygen (O2). Although oxygen is not the final electron acceptor, the process still uses a respiratory electron transport chain. In aerobic organisms undergoing r ...

. However, it is not known if multi-step processes such as

photosynthesis Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored in ...

chemosynthesis In biochemistry, chemosynthesis is the biological conversion of one or more carbon-containing molecules (usually carbon dioxide or methane) and nutrients into organic matter using the oxidation of inorganic compounds (e.g., hydrogen gas, hydrog ...

are used in radiosynthesis.

Discovery

Radiotrophic fungi were discovered in 1991 growing inside and around the

. It was specifically noted that colonies of

rich fungi had begun to rapidly grow within the cooling waters of the reactors within the power plant, turning them black. While there are many cases of

extremophiles An extremophile (from Latin ' meaning "extreme" and Greek ' () meaning "love") is an organism that is able to live (or in some cases thrive) in extreme environments, i.e. environments that make survival challenging such as due to extreme tempe ...

(organisms that can live in severe conditions such as that of the radioactive power plant) microbiologist

Arturo Casadevall Arturo Casadevall is a Bloomberg Distinguished Professor of Molecular Microbiology & Immunology and Infectious Diseases at the Johns Hopkins Bloomberg School of Public Health and Johns Hopkins School of Medicine, and the Alfred and Jill Somme ...

believed that these fungi were growing because of the

rather than in spite of it. Further research conducted at the

Albert Einstein College of Medicine Albert Einstein College of Medicine is a research-intensive medical school located in the Morris Park neighborhood of the Bronx in New York City. Founded in 1953, Einstein operates as an independent degree-granting institution as part of t ...

showed that three melanin-containing fungi—''

Cladosporium sphaerospermum ''Cladosporium sphaerospermum'' is a radiotrophic fungus belonging to the genus ''Cladosporium'' and was described in 1886 by Albert Julius Otto Penzig from the decaying leaves and branches of ''Citrus''. It is a dematiaceous (darkly-pigmented) ...

'', '' Wangiella dermatitidis'', and ''

Cryptococcus neoformans ''Cryptococcus neoformans'' is an encapsulated yeast belonging to the class Tremellomycetes and an obligate aerobe that can live in both plants and animals. Its teleomorph is a filamentous fungus, formerly referred to ''Filobasidiella neoformans ...

''—increased in

biomass Biomass is plant-based material used as a fuel for heat or electricity production. It can be in the form of wood, wood residues, energy crops, agricultural residues, and waste from industry, farms, and households. Some people use the terms bio ...

and accumulated

acetate An acetate is a salt formed by the combination of acetic acid with a base (e.g. alkaline, earthy, metallic, nonmetallic or radical base). "Acetate" also describes the conjugate base or ion (specifically, the negatively charged ion called ...

faster in an environment in which the

level was 500 times higher than in the normal environment. Exposure of '' C. neoformans''

cells Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Locations * Monastic cell, a small room, hut, or cave in which a religious recluse lives, alternatively the small precursor of a monastery w ...

to these

levels rapidly (within 20–40 minutes of exposure) altered the chemical properties of its

, and increased melanin-mediated rates of

electron transfer Electron transfer (ET) occurs when an electron relocates from an atom or molecule to another such chemical entity. ET is a mechanistic description of certain kinds of redox reactions involving transfer of electrons. Electrochemical processes ar ...

(measured as reduction of

ferricyanide Ferricyanide is the anion e(CN)6sup>3−. It is also called hexacyanoferrate(III) and in rare, but systematic nomenclature, hexacyanidoferrate(III). The most common salt of this anion is potassium ferricyanide, a red crystalline material that ...

NADH Nicotinamide adenine dinucleotide (NAD) is a coenzyme central to metabolism. Found in all living cells, NAD is called a dinucleotide because it consists of two nucleotides joined through their phosphate groups. One nucleotide contains an aden ...

) three- to four-fold compared with unexposed cells. Similar effects on

electron-transport capability were observed by the authors after exposure to

non-ionizing Non-ionizing (or non-ionising) radiation refers to any type of electromagnetic radiation that does not carry enough energy per quantum (photon energy) to ionize atoms or molecules—that is, to completely remove an electron from an atom or m ...

radiation, suggesting that melanotic fungi might also be able to use light or heat

for growth.

Role of melanin

Melanin Melanin (; from el, μέλας, melas, black, dark) is a broad term for a group of natural pigments found in most organisms. Eumelanin is produced through a multistage chemical process known as melanogenesis, where the oxidation of the amino ...

s are a family of naturally-occurring ancient pigments with radio-protective properties that are generally dark brown/black. It is important to note that melanin has a high molecular weight. This pigment can transduce and shield energy, therefore it can absorb

electromagnetic radiation In physics, electromagnetic radiation (EMR) consists of waves of the electromagnetic (EM) field, which propagate through space and carry momentum and electromagnetic radiant energy. It includes radio waves, microwaves, infrared, (visib ...

, including light. This quality means that

can protect melanized fungi from ionizing radiation. The energy transduction enhances growth in the fungi as well, meaning that melanized fungi grow faster.

is also an advantage to the fungus in that it helps it survive in many different, more extreme, and varying environments. Examples of these environments include the damaged reactor at

Chernobyl Chernobyl ( , ; russian: Чернобыль, ) or Chornobyl ( uk, Чорнобиль, ) is a partially abandoned city in the Chernobyl Exclusion Zone, situated in the Vyshhorod Raion of northern Kyiv Oblast, Ukraine. Chernobyl is about n ...

, the

International Space Station The International Space Station (ISS) is the largest Modular design, modular space station currently in low Earth orbit. It is a multinational collaborative project involving five participating space agencies: NASA (United States), Roscosmos ( ...

, and the Antarctic mountains. Melanin may also be able to help the fungus metabolize

into energy, but more evidence and research is still needed.

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 A cell wall is a structural layer surrounding some types of cells, just outside the cell membrane. It can be tough, flexible, and sometimes rigid. It provides the cell with both structural support and protection, and also acts as a filtering mec ...

or toxic intermediates formed in melanin biosynthesis have been suggested to contribute to this phenomenon. 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. The exact biochemical processes in the suggested melanin-based synthesis of organic compounds or other

metabolite In biochemistry, a metabolite is an intermediate or end product of metabolism. The term is usually used for small molecules. Metabolites have various functions, including fuel, structure, signaling, stimulatory and inhibitory effects on enzymes, ...

s 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.

Use in human spaceflight

It is hypothesized that radiotrophic fungi could potentially be used as a shield to protect against

, specifically in affiliation to the use of astronauts in space or other atmospheres. An experiment taking place at the

in December 2018 through January 2019 was conducted in order to test whether the use of radiotrophic fungi could aid in protection against ionizing radiation in space, as part of research efforts preceding a possible trip to

Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury. In the English language, Mars is named for the Roman god of war. Mars is a terrestrial planet with a thin at ...

. This experiment used the radiotrophic strain of the fungi ''

''. The growth of this fungi and its ability to deflect the effects of

ionizing radiation Ionizing radiation (or ionising radiation), including nuclear radiation, consists of subatomic particles or electromagnetic waves that have sufficient energy to ionize atoms or molecules by detaching electrons from them. Some particles can travel ...

were studied for 30 days aboard the

. This experimental trial yielded very promising results. The amount of

deflected was found to have a direct correlation to the amount of fungus. There was no difference in the reduction of

between the experimental and control group within the first 24 hour period, however once the radiotrophic fungi had reached an adequate maturation, and with a 180° protection radius, it was found that amounts of

were significantly reduced as compared to the control group. With a 1.7 mm thick shield of melanized radiotrophic ''

'', measurements of

nearing the end of the experimental trial were found to be 2.42% lower, demonstrating

deflecting capabilities five times that of the control group. Under circumstances in which the fungi would fully encompass an entity,

levels would be reduced by an estimated 4.34±0.7%. Estimations indicate that approximately a 21 cm thick layer could significantly deflect the annual amount of

received on

’ 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 Mass is an intrinsic property of a body. It was traditionally believed to be related to the quantity of matter in a physical body, until the discovery of the atom and particle physics. It was found that different atoms and different ele ...

on potential

missions, a mixture with equal mole concentration of Martian soil,

, and a layer of fungi roughly 9 cm thick, could be used.

References

{{Reflist, refs= {{cite journal , title = Relationship between secondary metabolism and fungal development , vauthors=Calvo AM, Wilson RA, Bok JW, Keller NP , year = 2002 , journal = Microbiol Mol Biol Rev , volume = 66 , pages = 447–459 , pmid = 12208999 , doi = 10.1128/MMBR.66.3.447-459.2002 , issue = 3 , pmc = 120793 {{cite journal , title = Ionizing radiation changes the electronic properties of melanin and enhances the growth of melanized fungi , editor1-first = Julian , editor1-last = Rutherford , vauthors = Dadachova E, Bryan RA, Huang X, Moadel T, Schweitzer AD, Aisen P, Nosanchuk JD, Casadevall A , year = 2007 , journal = PLOS ONE , volume = 2 , pages = e457 , pmid = 17520016 , doi =10.1371/journal.pone.0000457 , issue = 5 , pmc = 1866175 , bibcode = 2007PLoSO...2..457D , doi-access = free {{Cite magazine , url=http://www.sciencenews.org/articles/20070526/fob5.asp , archiveurl=https://web.archive.org/web/20080424001002/http://www.sciencenews.org/articles/20070526/fob5.asp , archivedate=2008-04-24 , magazine=Science News , title=Dark Power: Pigment seems to put radiation to good use , date=May 26, 2007 , volume=171 , number=21 , page=325 , first=Davide , last=Castelvecchi

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