Certain fungi, most of them darkly pigmented with melanin, appear to harness ionizing radiation in a way that boosts their growth and metabolism. The phenomenon, sometimes called radiosynthesis or radiotropism, was first noticed in the ruins of the Chernobyl nuclear reactor, where melanized fungi were found thriving in conditions lethal to most life. Whether this process is truly analogous to photosynthesis or something subtler remains one of the more fascinating open questions in microbiology.
Thriving Where Nothing Should
The story starts in the early 2000s, when researchers sampling the interior of Chernobyl’s destroyed Reactor No. 4 kept finding melanin-rich fungi growing on the reactor walls and even in the cooling water. These weren’t just surviving; many appeared to be doing better in the presence of radiation than without it. The species involved, including Cladosporium sphaerospermum, Wangiella dermatitidis, and Cryptococcus neoformans, all share a key trait: they produce large quantities of melanin, the same broad class of pigment responsible for dark skin, hair, and feathers in animals.
Chernobyl wasn’t the only clue. Melanized fungi have turned up on the International Space Station, in the highlands of Antarctica where UV exposure is extreme, and in other high-radiation niches around the world. The pattern kept repeating: dark, melanin-heavy fungi seemed drawn to radiation rather than repelled by it. Researchers coined the term “radiotropism” to describe this apparent directional growth toward radioactive sources, echoing the way plants grow toward light.
What Melanin Actually Does With Radiation
Melanin is an unusual molecule. Unlike most biological pigments that absorb a narrow slice of the electromagnetic spectrum, melanin absorbs broadly, from ultraviolet light through visible wavelengths and into ionizing radiation like gamma rays. That broad absorption is well established. The harder question is what happens to the energy once melanin captures it.
The clearest experimental evidence comes from electrochemical work showing that gamma radiation continuously oxidizes melanin, shifting its chemical balance in a way that generates a small but measurable electric current. This effect was most pronounced when a chemical reductant was present, which allowed melanin to keep cycling between oxidized and reduced states rather than hitting a dead end. In other words, radiation appears to push melanin into a sustained electrochemical loop that produces energy in a form cells could potentially use.1PubMed. Gamma radiation interacts with melanin to alter its oxidation-reduction potential and results in electric current production
Melanin’s radioprotective side matters too. The pigment shields fungal cells from radiation damage, and that shielding depends on several physical properties working together: its chemical makeup, the presence of stable free radicals that can absorb and neutralize reactive species, and even its spatial arrangement within the cell. Melanin granules tend to form spherical shells around the cell, creating a kind of armor layer that scatters and absorbs incoming radiation before it reaches DNA and other vulnerable molecules.2Pigment Cell & Melanoma Research. The radioprotective properties of fungal melanin are a function of its chemical composition, stable radical presence and spatial arrangement
So melanin appears to play a double role: it protects the cell from radiation damage and simultaneously captures some of that radiation’s energy. This combination is what makes the comparison to chlorophyll so tempting, though the analogy has limits that are worth understanding.
Is It Really Like Photosynthesis?
The idea that melanin could function like chlorophyll, converting radiation into metabolic energy, is the headline-grabbing claim. And multiple research groups have raised it seriously, noting that the combination of radiotropism, enhanced growth under irradiation, and melanin’s energy-transduction properties points toward something genuinely analogous to photosynthesis.3PubMed Central. Ionizing radiation: how fungi cope, adapt, and exploit with the help of melanin But the scientific community hasn’t reached consensus, and for good reason.
Photosynthesis is a tightly organized system. Chlorophyll doesn’t just absorb light; it feeds that energy into an elaborate chain of proteins and enzymes that ultimately build sugar from carbon dioxide and water. No one has identified an equivalent downstream pathway in melanized fungi. The electric current melanin generates under irradiation is real, but the precise mechanism by which fungal cells would capture that energy and channel it into growth is still unclear. It could be that melanin-derived energy contributes a small metabolic boost, enough to give these fungi a competitive edge in irradiated environments, without being a full-blown energy harvesting system on the scale of photosynthesis.
The enhanced growth observed under irradiation is itself somewhat modest. Fungi don’t photosynthesize-style double in size under a gamma source. They still rely primarily on chemical nutrients. What radiation seems to provide, based on current evidence, is a supplementary energy input that slightly accelerates metabolism in melanized species. Think of it less as “fungi powered by radiation” and more as “fungi that get a small energy bonus from radiation that would kill most other organisms.”
What Happens Inside Irradiated Fungal Cells
Melanin tells only part of the story. When researchers looked at the genome-wide response of Cryptococcus neoformans to gamma radiation, the picture was more complex than just a pigment absorbing energy. Exposure to radiation triggered a cascade of genetic changes: genes involved in DNA repair ramped up, as expected for any organism under radiation stress. But a range of oxidative stress response genes also increased their activity, along with genes for molecular chaperones (proteins that help other proteins fold correctly under stress), ubiquitination systems (which tag damaged proteins for recycling), and autophagy (the cell’s self-cleaning process).4PubMed Central. Unraveling Fungal Radiation Resistance Regulatory Networks through the Genome-Wide Transcriptome and Genetic Analyses of Cryptococcus neoformans
Meanwhile, genes for protein and fatty acid synthesis were dialed down. The cell appears to shift into a damage-control mode, prioritizing repair and cleanup over growth and production. This is a sophisticated, coordinated survival strategy, not just passive shielding by melanin. It suggests that radiation-resistant fungi have evolved multiple layers of defense: melanin as a frontline physical and chemical barrier, and a deep set of molecular repair systems as the backup.
This genomic work also hints at why melanin alone isn’t the whole explanation for radiation resistance. Even non-melanized mutants of C. neoformans show some degree of radiation tolerance, though less than their melanized counterparts. The full radiation resistance phenotype seems to require both the pigment and the cellular repair machinery working in concert.
Not All Melanins Offer the Same Protection
Fungi produce several chemically distinct types of melanin. The two most common are DOPA melanin (similar to the melanin in human skin) and DHN melanin (named for one of its chemical precursors, 1,8-dihydroxynaphthalene). These molecules share certain properties, like broad-spectrum absorption, but they aren’t interchangeable.
A study comparing two black fungi, Knufia petricola and Cryomyces antarcticus, found that DHN melanin provided meaningful UV-B protection in C. antarcticus but was ineffective in K. petricola, even though both species produce the same type of melanin. Even carotenoids, another class of protective pigment, failed to shield K. petricola.5PubMed Central. 1,8-Dihydroxynaphthalene (DHN) melanin provides unequal protection to black fungi Knufia petricola and Cryomyces antarcticus from UV-B radiation The implication is that melanin’s protective value depends on context: how it’s distributed within the cell, what other molecules are present, and probably the organism’s overall stress-response toolkit.
This variability matters for anyone hoping to harness fungal melanin for practical applications. You can’t simply extract melanin from any dark fungus and expect uniform radiation shielding. The pigment’s effectiveness is deeply tied to the biology of the organism producing it.
A Living Radiation Shield for Space Travel
One of the more creative applications researchers have explored is using radiotrophic fungi as biological radiation shields for astronauts. Deep space travel exposes crews to galactic cosmic rays and solar particle events, and current shielding technology adds enormous weight to spacecraft. A living shield that grows, repairs itself, and requires only basic nutrients would be transformative.
An experiment aboard the International Space Station tested this idea directly. Researchers grew a thin lawn of Cladosporium sphaerospermum, one of the Chernobyl-associated species, on one side of a radiation detector and left the other side unshielded as a control. At full maturity, the fungal layer, only about 1.7 millimeters thick, reduced radiation readings by roughly 2% compared to the control. Extrapolating that to a fungal layer fully surrounding an object, the researchers estimated it could block about 4-5% of the measured radiation spectrum.6bioRxiv. A Self-Replicating Radiation-Shield for Human Deep-Space Exploration: Radiotrophic Fungi can Attenuate Ionizing Radiation aboard the International Space Station
Those numbers might sound small, but there are two things to appreciate. First, the fungal lawn was extremely thin; a thicker layer would presumably block more. Second, the fungus showed about 21% faster growth in space compared to ground controls, supporting the idea that radiotropism works with the kind of mixed radiation environment found in orbit, not just the controlled gamma sources used in labs. A shield that actively grows thicker in response to the radiation it’s blocking is an appealing concept, even if the attenuation per millimeter needs to improve before it becomes practical.
Other research has modeled thicker melanin-based shields using a biomimetic approach. One study found that melanized fungi thrive in environments with high radionuclide concentrations and explored how synthetic versions of their shielding architecture might be engineered for human use.7PubMed Central. A biomimetic approach to shielding from ionizing radiation: The case of melanized fungi The idea is to learn from the fungus rather than grow it directly, using melanin’s properties in engineered materials.
Cleaning Up Contaminated Sites
Back on Earth, the same fungi that fascinate astrobiologists have caught the attention of environmental scientists working on nuclear decontamination. Fungi found in radioactive environments can absorb ionizing radiation and deposit radioisotopes in their cell walls, effectively pulling radioactive material out of soil and water. Some species also consume organic matter associated with nuclear sites, including the graphite present in Chernobyl’s damaged reactor core.8Research, Society and Development. Radiotrophic fungi and their use as bioremediation agents of areas affected by radiation and as protective agents
This makes radiotrophic fungi potential candidates for bioremediation, the use of living organisms to clean up pollution. The logic is straightforward: if these fungi naturally accumulate radioactive material in their biomass, you could grow them at a contaminated site, let them absorb radionuclides, then harvest and safely dispose of the fungal mass. It’s a gentler and potentially cheaper approach than stripping contaminated soil or filtering water through synthetic materials.
Fungal melanins also show promise for heavy metal chelation and absorption of organic pollutants beyond just radioactive material. The pigment’s complex chemical structure gives it an unusual ability to bind a range of contaminants, which opens up potential applications in cleaning up industrial sites even where radiation isn’t the primary concern.9PubMed Central. Fungal Melanins and Applications in Healthcare, Bioremediation and Industry
When Fungi Attack Nuclear Infrastructure
The relationship between fungi and the nuclear industry isn’t always cooperative. While bioremediation researchers want to deploy fungi at contaminated sites, engineers responsible for nuclear waste storage have a different concern: fungi can damage the concrete barriers designed to contain radioactive waste.
A year-long study exposed concrete chips, similar to those used in nuclear waste disposal facilities, to several fungal species. After twelve months, the concrete showed visible deterioration including expansion, discoloration, cracking, and spalling. Aspergillus niger, a common mold, was particularly aggressive. Electron microscopy revealed fungal hyphae penetrating the concrete surface, and chemical analysis identified calcium oxalate crystals, both the monohydrate and dihydrate forms, forming within and on top of the concrete. The fungi were essentially dissolving calcium from the cement matrix and redepositing it as oxalate minerals, physically and chemically weakening the barrier.10Geomicrobiology Journal. Fungal Deterioration of Barrier Concrete used in Nuclear Waste Disposal
This is a genuinely underappreciated problem. Nuclear waste repositories are designed to last centuries or millennia. If common fungi can visibly degrade barrier concrete within a single year under laboratory conditions, the long-term integrity of waste containment structures in real-world environments, where fungal spores are ubiquitous, deserves more attention than it typically receives. The fungi involved don’t even need to be radiation-resistant specialists; ordinary environmental molds can do the job.
The Energy Harvesting Frontier
Beyond shielding and bioremediation, the electrochemical properties of melanin under radiation have sparked interest in bio-electronic applications. If melanin generates electric current when irradiated, and if that generation can be sustained by cycling between oxidation and reduction states, then melanin-based materials could theoretically serve as components in radiation-powered energy harvesting devices.1PubMed. Gamma radiation interacts with melanin to alter its oxidation-reduction potential and results in electric current production
This is still early-stage research. The currents involved are tiny, and scaling melanin-based energy harvesting to anything practical would require significant advances in material science. But the concept is intriguing: a biocompatible, self-assembling pigment that converts radiation, including the ambient radiation present everywhere on Earth and in much higher doses in space, into electricity. It’s a long way from a melanin-based battery, but the fundamental physics appears to work.
Researchers have also noted that melanin’s energy-transduction properties raise broader questions about whether melanin plays unrecognized roles in other organisms, including humans. Melanin is abundant in human skin, eyes, brain tissue, and the inner ear. Whether any of these melanin deposits do something useful with the low levels of background radiation we all absorb remains entirely speculative, but the question is no longer absurd given what we’ve learned from fungi.11PubMed Central. Melanin, Radiation, and Energy Transduction in Fungi
What Remains Genuinely Uncertain
For all the exciting leads, this field has some significant gaps. The biggest is the missing metabolic pathway. If melanin-derived energy feeds into fungal metabolism, there should be identifiable biochemical steps between “melanin absorbs gamma ray” and “cell uses energy to grow.” Nobody has mapped those steps. Without that pathway, the radiosynthesis claim remains suggestive rather than proven. Enhanced growth under irradiation could have alternative explanations, including radiation-induced hormesis (a low-dose stimulatory effect seen in many organisms) or changes in nutrient cycling caused by radiation’s effects on the growth medium.
The quantitative significance of the energy contribution is also unclear. Even in the most enthusiastic framing, no one suggests melanin-based radiosynthesis could sustain a fungus on its own. These organisms need organic carbon and other nutrients just like any other fungus. The radiation-derived energy, if real, appears to be a supplement, not a primary fuel source. How large that supplement is, whether it’s a few percent boost or something more substantial, hasn’t been nailed down.
There’s also the challenge of separating radioprotection from radiosynthesis experimentally. If melanin protects DNA from damage, melanized fungi would be expected to grow faster than non-melanized ones under radiation simply because they sustain less damage, not because they’re harvesting energy. Distinguishing “grows better because it’s less injured” from “grows better because it has an extra energy source” requires careful controls, and not all studies have achieved them.
Fungi on the Walls of Chernobyl’s Sarcophagus
Perhaps the most vivid image in this entire research area is the black fungal growth observed coating the interior walls of the Chernobyl containment structure. These organisms colonized one of the most radioactive human-made environments on the planet, growing toward the radiation source rather than away from it. Robots sent inside found melanized fungi thriving on the concrete and even in the water used to cool the remains of the reactor core.3PubMed Central. Ionizing radiation: how fungi cope, adapt, and exploit with the help of melanin
These organisms didn’t evolve at Chernobyl. Many of the same species exist in ordinary environments worldwide, including on the surfaces of buildings, in soil, and in kitchens. The Chernobyl environment simply revealed a capacity that had been there all along, likely evolved over billions of years of exposure to natural background radiation and UV light. Some researchers have speculated that early in Earth’s history, when the planet’s surface radiation was more intense and the ozone layer had not yet formed, melanin-based energy capture may have been more biologically important than it is today. If that’s right, radiosynthetic fungi aren’t evolutionary newcomers exploiting a human-made disaster. They’re ancient organisms whose old tricks suddenly became visible under extreme modern conditions.