Radiotrophic fungus

Last updated
Cryptococcus neoformans stained with light India ink Cryptococcus neoformans using a light India ink staining preparation PHIL 3771 lores.jpg
Cryptococcus neoformans stained with light India ink

Radiotrophic fungi are fungi that can perform the hypothetical biological process called radiosynthesis, which means using ionizing radiation as an energy source to drive metabolism. It has been claimed that radiotrophic fungi have been found in extreme environments such as in the Chernobyl Nuclear Power Plant.

Contents

Most radiotrophic fungi use melanin in some capacity to survive. [1] The process of using radiation and melanin for energy has been termed radiosynthesis, and is thought to be analogous to anaerobic respiration. [2] However, it is not known if multi-step processes such as photosynthesis or chemosynthesis are used in radiosynthesis or even if radiosynthesis exists in living organisms.

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”. [3] [4] 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. [4] 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. [5] 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. [6]

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. Exposure of C. neoformans cells to these radiation levels rapidly (within 20–40 minutes of exposure) altered the chemical properties of its melanin, and increased melanin-mediated rates of electron transfer (measured as reduction of ferricyanide by NADH) three- to four-fold compared with unexposed cells. 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. [6]

Outside of the fungal studies, similar effects on melanin electron-transport capability were observed by the authors after exposure to non-ionizing radiation. The authors did not conclude whether light or heat radiation would have a similar effect on living fungal cells. [6]

Role of melanin

Melanins are an ancient family of dark-colored, naturally occurring pigments with radiation-shielding properties. These pigments can absorb electromagnetic radiation due to their dark color and high molecular weights; 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. [7] 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, the International Space Station, and the Transantarctic Mountains. Melanin may also be able to help the fungus metabolize radiation, but more evidence and research is still needed. [1]

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. [6] 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. [8] 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.

Use in human spaceflight

It is hypothesized that radiotrophic fungi could potentially be used as a shield to protect against radiation, [2] specifically in affiliation 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 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. This experiment used the radiotrophic strain of the fungi Cladosporium sphaerospermum . [2] The growth of this fungi 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 have a direct correlation to 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 radiotrophic fungi had reached an adequate maturation, and with a 180° protection radius, it was found that 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%. [2] 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. [2]

See also

Related Research Articles

<span class="mw-page-title-main">Melanin</span> Group of natural pigments found in most organisms

Melanin consist of oligomers or polymers arranged in a disordered manner which among other functions provide the pigments of many organisms. Melanin pigments are produced in a specialized group of cells known as melanocytes. They have been described as "among the last remaining biological frontiers with the unknown".

<i>Cryptococcus neoformans</i> Species of yeast

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. In its yeast state, it is often found in bird excrement. Cryptococcus neoformans can cause disease in apparently immunocompetent, as well as immunocompromised, hosts.

<span class="mw-page-title-main">Effects of the Chernobyl disaster</span> Assessment of Chernobyls impact on Earth since 1986

The 1986 Chernobyl disaster triggered the release of radioactive contamination into the atmosphere in the form of both particulate and gaseous radioisotopes. As of 2022, it was the world's largest known release of radioactivity into the environment.

<i>Sporothrix schenckii</i> Species of fungus

Sporothrix schenckii, a fungus that can be found worldwide in the environment, is named for medical student Benjamin Schenck, who in 1896 was the first to isolate it from a human specimen. The species is present in soil as well as in and on living and decomposing plant material such as peat moss. It can infect humans as well as animals and is the causative agent of sporotrichosis, commonly known as "rose handler's disease." The most common route of infection is the introduction of spores to the body through a cut or puncture wound in the skin. Infection commonly occurs in otherwise healthy individuals but is rarely life-threatening and can be treated with antifungals. In the environment it is found growing as filamentous hyphae. In host tissue it is found as a yeast. The transition between the hyphal and yeast forms is temperature dependent making S. schenckii a thermally dimorphic fungus.

<span class="mw-page-title-main">Mycelial cord</span> Structure produced by fungi

Mycelial cords are linear aggregations of parallel-oriented hyphae. The mature cords are composed of wide, empty vessel hyphae surrounded by narrower sheathing hyphae. Cords may look similar to plant roots, and also frequently have similar functions; hence they are also called rhizomorphs. As well as growing underground or on the surface of trees and other plants, some fungi make mycelial cords which hang in the air from vegetation.

<i>Setosphaeria rostrata</i> Pathogenic fungus

Setosphaeria rostrata is a heat tolerant fungus with an asexual reproductive form (anamorph) known as Exserohilum rostratum. This fungus is a common plant pathogen, causing leaf spots as well as crown rot and root rot in grasses. It is also found in soils and on textiles in subtropical and tropical regions. Exserohilum rostratum is one of the 35 Exserohilum species implicated uncommonly as opportunistic pathogens of humans where it is an etiologic agent of sinusitis, keratitis, skin lesions and an often fatal meningoencephalitis. Infections caused by this species are most often seen in regions with hot climates like Israel, India and the southern USA.

Pathogenic fungi are fungi that cause disease in humans or other organisms. Although fungi are eukaryotic, many pathogenic fungi are microorganisms. Approximately 300 fungi are known to be pathogenic to humans; their study is called "medical mycology". Fungal infections are estimated to kill more people than either tuberculosis or malaria—about two million people per year.

<span class="mw-page-title-main">Fungus</span> Biological kingdom, separate from plants and animals

A fungus 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 one of the traditional eukaryotic kingdoms, along with Animalia, Plantae and either Protista or Protozoa and Chromista.

Black yeasts, sometimes also black fungi, dematiaceous fungi, microcolonial fungi or meristematic fungi is a diverse group of slow-growing microfungi which reproduce mostly asexually. Only few genera reproduce by budding cells, while in others hyphal or meristematic (isodiametric) reproduction is preponderant. Black yeasts share some distinctive characteristics, in particular a dark colouration (melanisation) of their cell wall. Morphological plasticity, incrustation of the cell wall with melanins and presence of other protective substances like carotenoids and mycosporines represent passive physiological adaptations which enable black fungi to be highly resistant against environmental stresses. The term "polyextremotolerance" has been introduced to describe this phenotype, an example of which is the species Aureobasidium pullulans. Presence of 1,8-dihydroxynaphthalene melanin in the cell wall confers to the microfungi their characteristic olivaceous to dark brown/black colour.

<i>Cladophialophora bantiana</i> Species of fungus

Cladophialophora bantiana is a melanin producing mold known to cause brain abscesses in humans. It is one of the most common causes of systemic phaeohyphomycosis in mammals. Cladophialophora bantiana is a member of the ascomycota and has been isolated from soil samples from around the world.

Dark septate endophytes (DSE) are a group of endophytic fungi characterized by their morphology of melanized, septate, hyphae. This group is likely paraphyletic, and contain conidial as well as sterile fungi that colonize roots intracellularly or intercellularly. Very little is known about the number of fungal taxa within this group, but all are in the Ascomycota. They are found in over 600 plant species and across 114 families of angiosperms and gymnosperms and co-occur with other types of mycorrhizal fungi. They have a wide global distribution and can be more abundant in stressed environments. Much of their taxonomy, physiology, and ecology are unknown.

<span class="mw-page-title-main">Arturo Casadevall</span> Cuban-American scientist

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 Sommer Professor and Chair of the W. Harry Feinstone Department of Molecular Microbiology and Immunology at the Johns Hopkins Bloomberg School of Public Health. He is an internationally recognized expert in infectious disease research, with a focus on fungal and bacterial pathogenesis and basic immunology of antibody structure-function. He was elected a member of the National Academy of Sciences in 2022.

<span class="mw-page-title-main">Bioremediation of radioactive waste</span>

Bioremediation of radioactive waste or bioremediation of radionuclides is an application of bioremediation based on the use of biological agents bacteria, plants and fungi to catalyze chemical reactions that allow the decontamination of sites affected by radionuclides. These radioactive particles are by-products generated as a result of activities related to nuclear energy and constitute a pollution and a radiotoxicity problem due to its unstable nature of ionizing radiation emissions.

<i>Zasmidium cellare</i> Species of fungus

Zasmidium cellare, also known as cellar mold, is a species of fungus that exists in dark, ethanol-rich environments and is brown to black in colour. This species primarily exists in wine and brandy cellars in central and southern Europe, but can be found in surrounding regions and is thought to be helpful in the wine making process by some and a hygienic issue by others. Not much is known about Z. cellare's sexual biology and is thought to be beneficial to the cleanliness of cellar air due to its ability to consume musty odours.

<i>Cladophialophora carrionii</i> Species of fungus

Cladophialophora carrionii is a melanized fungus in the genus Cladophialophora that is associated with decaying plant material like cacti and wood. It is one of the most frequent species of Cladophialophora implicated in human disease. Cladophialophora carrionii is a causative agent of chromoblastomycosis, a subcutaneous infection that occurs in sub-tropical areas such as Madagascar, Australia and northwestern Venezuela. Transmission occurs through traumatic implantation of plant material colonized by C. carrionii, mainly infecting rural workers. When C. carrionii infects its host, it transforms from a mycelial state to a muriform state to better tolerate the extreme conditions in the host's body.

<i>Cladosporium sphaerospermum</i> Species of fungus

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) fungus characterized by slow growth and largely asexual reproduction. Cladosporium sphaerospermum consists of a complex of poorly morphologically differentiated, "cryptic" species that share many physiological and ecological attributes. In older literature, all of these sibling species were classified as C. sphaerospermum despite their unique nature. Accordingly, there is confusion in older literature reports on the physiological and habitat regularities of C. sphaerospermum in the strict sense. This fungus is most phylogenetically similar to C. fusiforme. According to modern phylogenetic analyses, the previously synonymized species, Cladosporium langeroni, is a distinct species.

Radiosynthesis is the theorized capture and metabolism, by living organisms, of energy from ionizing radiation, analogously to photosynthesis. Metabolism of ionizing radiation was theorized as early as 1956 by the Russian microbiologist S. I. Kuznetsov.

Cladosporium oxysporum is an airborne fungus that is commonly found outdoors and is distributed throughout the tropical and subtropical region, it is mostly located In Asia and Africa. It spreads through airborne spores and is often extremely abundant in outdoor air during the spring and summer seasons. It mainly feeds on decomposing organic matter in warmer climates, but can also be parasitic and feed on living plants. The airborne spores can occasionally cause cutaneous infections in humans, and the high prevalence of C. oxysporum in outdoor air during warm seasons contributes to its importance as an etiological agent of allergic disease and possibly human cutaneous phaeohyphomycosis in tropical regions.

Cladosporium herbarum is a common fungus found worldwide in organic and inorganic matter. It is efficiently distributed in the air, where it exists as the most frequently occurring fungal species. It can grow over a wide range of temperatures including very cold environments, giving it the ability to grow on refrigerated meat and form "black spots". Its high prevalence in the air and production of allergens makes C. herbarum an important exacerbant of asthma and hay fever.

Cladophialophora arxii is a black yeast shaped dematiaceous fungus that is able to cause serious phaeohyphomycotic infections. C. arxii was first discovered in 1995 in Germany from a 22-year-old female patient suffering multiple granulomatous tracheal tumours. It is a clinical strain that is typically found in humans and is also capable of acting as an opportunistic fungus of other vertebrates Human cases caused by C. arxii have been reported from all parts of the world such as Germany and Australia.

References

  1. 1 2 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. PMC   2677413 . PMID   18848901.
  2. 1 2 3 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 .
  3. ↑ 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. Bibcode:2022NatSR..1212142B. doi:10.1038/s41598-022-16063-z. PMC   9287308 . PMID   35840596.
  4. 1 2 Zhdanova, Nelli N.; Tugay, Tatyana; Dighton, John; Zheltonozhsky, Victor; McDermott, Patrick (September 2004). "Ionizing radiation attracts soil fungi". Mycological Research. Vol. 108, no. Pt 9. pp. 1089–1096. doi:10.1017/s0953756204000966. ISSN   0953-7562. PMID   15506020 . Retrieved 2023-04-11.
  5. ↑ Castelvecchi, Davide (May 26, 2007). "Dark Power: Pigment seems to put radiation to good use". Science News. Vol. 171, no. 21. p. 325. Archived from the original on 2008-04-24.
  6. 1 2 3 4 Dadachova E, Bryan RA, Huang X, Moadel T, Schweitzer AD, Aisen P, Nosanchuk JD, Casadevall A (2007). Rutherford J (ed.). "Ionizing radiation changes the electronic properties of melanin and enhances the growth of melanized fungi". PLOS ONE. 2 (5): e457. Bibcode:2007PLoSO...2..457D. doi: 10.1371/journal.pone.0000457 . PMC   1866175 . PMID   17520016.
  7. ↑ Gessler, N. N.; Egorova, A. S.; Belozerskaya, T. A. (2014). "Melanin pigments of fungi under extreme environmental conditions (Review)". Applied Biochemistry and Microbiology. 50 (2): 105–113. doi: 10.1134/S0003683814020094 . ISSN   0003-6838 – via Springer.
  8. ↑ Calvo AM, Wilson RA, Bok JW, Keller NP (2002). "Relationship between secondary metabolism and fungal development". Microbiol Mol Biol Rev. 66 (3): 447–459. doi:10.1128/MMBR.66.3.447-459.2002. PMC   120793 . PMID   12208999.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.