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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 from ...
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 border, ...
.
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, 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 re ...
.
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 i ...
or
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, hydro ...
are used in radiosynthesis.
Discovery
Radiotrophic fungi were discovered in 1991 growing inside and around 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 border, ...
. It was specifically noted that colonies of
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 ...
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 temper ...
(organisms that can live in severe conditions such as that of the radioactive power plant) microbiologist
Arturo Casadevall believed that these fungi were growing because of the
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 ...
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'', ''
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 neoforman ...
''—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 bi ...
and accumulated
acetate
An acetate is a salt (chemistry), salt formed by the combination of acetic acid with a base (e.g. Alkali metal, alkaline, Alkaline earth metal, earthy, Transition metal, metallic, nonmetallic or radical Radical (chemistry), base). "Acetate" als ...
faster in an environment in which the
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 ...
level was 500 times higher than in the normal environment. Exposure of ''
C. neoformans
''Cryptococcus neoformans'' is an encapsulated yeast belonging to the class (biology), class Tremellomycetes and an obligate aerobe that can live in both plants and animals. Its teleomorph is a filamentous fungus, formerly referred to ''Filobasid ...
''
cells to these
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 ...
levels rapidly (within 20–40 minutes of exposure) altered the chemical properties of its
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 ...
, 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 ...
by
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
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 ...
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 mol ...
radiation, suggesting that melanotic fungi might also be able to use light or heat
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 ...
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 field, electromagnetic (EM) field, which propagate through space and carry momentum and electromagnetic radiant energy. It includes radio waves, microwaves, inf ...
, including light. This quality means that
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 ...
can protect melanized fungi from ionizing radiation. The energy transduction enhances growth in the fungi as well, meaning that melanized fungi grow faster.
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 ...
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 no ...
, the
International Space Station
The International Space Station (ISS) is the largest modular space station currently in low Earth orbit. It is a multinational collaborative project involving five participating space agencies: NASA (United States), Roscosmos (Russia), JAXA ...
, and the Antarctic mountains. Melanin may also be able to help the fungus metabolize
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 ...
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 mech ...
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, c ...
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
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 ...
,
[ specifically in affiliation to the use of astronauts in space or other atmospheres. An experiment taking place at the ]International Space Station
The International Space Station (ISS) is the largest modular space station currently in low Earth orbit. It is a multinational collaborative project involving five participating space agencies: NASA (United States), Roscosmos (Russia), JAXA ...
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 (planet), Mercury. In the English language, Mars is named for the Mars (mythology), Roman god of war. Mars is a terr ...
. This experiment used the radiotrophic strain of the fungi '' Cladosporium sphaerospermum''. 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 International Space Station
The International Space Station (ISS) is the largest modular space station currently in low Earth orbit. It is a multinational collaborative project involving five participating space agencies: NASA (United States), Roscosmos (Russia), JAXA ...
. This experimental trial yielded very promising results.
The amount of 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 ...
deflected was found to have a direct correlation to the amount of fungus. There was no difference in the reduction 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 ...
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 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 significantly reduced as compared to the control group. With a 1.7 mm thick shield of melanized radiotrophic '' Cladosporium sphaerospermum'', measurements of 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 ...
nearing the end of the experimental trial were found to be 2.42% lower, demonstrating 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 ...
deflecting capabilities five times that of the control group. Under circumstances in which the fungi would fully encompass an entity, 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 ...
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 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 ...
received on Mars
Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury (planet), Mercury. In the English language, Mars is named for the Mars (mythology), Roman god of war. Mars is a terr ...
’ 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 elementar ...
on potential Mars
Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury (planet), Mercury. In the English language, Mars is named for the Mars (mythology), Roman god of war. Mars is a terr ...
missions, a mixture with equal mole concentration of Martian soil
Martian soil is the fine regolith (a blanket of unconsolidated, loose, heterogeneous superficial deposits covering solid rock) found on the surface of Mars. Its properties can differ significantly from those of terrestrial soil, including its to ...
, 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 ...
, and a layer of fungi roughly 9 cm thick, could be used.
See also
*
* Nylon-eating bacteria
References
{{Reflist, refs=
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, vauthors=Calvo AM, Wilson RA, Bok JW, Keller NP , year = 2002
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, 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
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, 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]
External links
Einstein College of Medicine on radiotrophic fungi
The blacker the better… especially in Chernobyl
at Earthling Nature.
Fungi by adaptation
Evolution by taxon
Radiation effects
Radiobiology
Gamma rays
Extremophiles