The fourth block, which exploded in 1986, was covered by a protective sarcophagus a few months later, where other radioactive debris from the site was collected. But already in 1991, when microbiologist Nelly Zhdanova and her colleagues examined these remnants using remotely controlled manipulators, life showed up here too. The deadly debris was found to be inhabited by thriving communities of black mushrooms.
Over the following years, representatives of about a hundred genera were identified among them. Some of them not only withstand the deadly level of radiation, but even themselves are drawn to it, like plants to light.
High-energy radiation is dangerous to all living things. It easily damages DNA, causing mutations and errors in the code. Heavy particles are capable of breaking up chemical compounds like cannonballs, leading to the appearance of active radicals, which immediately interact with the first neighbor they find. A sufficiently intense bombardment can cause radiolysis of water molecules and a whole shower of random reactions that kill the cell. Despite this, some creatures show amazing resistance to such effects.
Single-celled organisms have a relatively simple structure, and it is not so easy to disrupt their metabolism by free radicals, and powerful protein repair tools quickly repair damaged DNA. As a result, mushrooms are capable of absorbing up to 17,000 Gray of radiation energy - many orders of magnitude more than the amount safe for humans. Moreover, some of them literally enjoy such a radioactive "rain".
The famous Canyon of Evolution near Mount Carmel in Israel is oriented with one slope towards Europe, the other towards Africa. The difference between their illumination reaches 800%, and the "African" slope irradiated by the sun is inhabited by mushrooms that grow better in the presence of radiation. Like those found in Chernobyl, they appear black due to the large amounts of melanin. This pigment is able to intercept high-energy particles and dissipate their energy, keeping cells from damage.
Dissolving such a fungal cell, under a microscope, one can see its "ghost" - a black silhouette of melanin, which accumulates in concentric layers in the cell wall. Mushrooms from the "African" side of the canyon contain three times more of it than the inhabitants of the "European" slope. They are also rich in many microbes living in the highlands, which in natural conditions receive up to 500-1000 Gray per year. But even such a decent amount of absorbed radiation for mushrooms is nothing. It is unlikely that all this melanin is produced for protection alone.
Back in 1991, Nelly Zhdanova demonstrated that mushrooms collected near the Chernobyl nuclear power plant reach the source of radiation and grow better in its presence. In 2007, these results were developed by the biologists Arturo Casadevala and Ekaterina Dadachova working in the United States. Scientists have shown that under the influence of radiation hundreds of times higher than the natural background, black melanized fungi (Cladosporium sphaerospermum, Wangiella dermatitidis and Cryptococcus neoformans) absorb carbon from the nutrient medium three times more intensively. At the same time, mutant albino fungi, unable to produce melanin, tolerated radiation easily, but grew at the usual rate.
It is worth saying that melanin can be present in cells in slightly different chemical configurations. Its main form in humans is eumelanin, it protects the skin from ultraviolet radiation and gives it a brown-black color. The red color of the lips and nipples is determined by the presence of pheomelanin. And it is pheomelanin that is produced by fungal cells under the influence of radiation, although in such quantities it already looks completely black.
The transition from eu- to pheomelanin is accompanied by an increase in the transfer of electrons from NADP to ferricyanide - this is one of the first steps in glucose biosynthesis. It is not surprising that, according to some assumptions, such fungi are capable of carrying out reactions similar to photosynthesis, but instead of light they use the energy of radioactive radiation. This ability allows them to survive and thrive where more complex and finicky organisms die.
Large numbers of highly melanized fungal spores are found in the deposits of the Early Cretaceous. In that era, many animals and plants became extinct: “This period coincides with the transition through the“ magnetic zero ”and the temporary loss of the“ geomagnetic shield ”that protects the Earth from radiation,” writes Ekaterina Dadachova. Radiotrophic mushrooms could not help but take advantage of this situation. Sooner or later we will also use this.
The use of melanin to utilize radiation energy is still only a hypothesis. However, research continues, since the radiotroph is not something exotic. In conditions of a lack of resources and sufficient radiation, some common fungi can enhance melanin synthesis and exhibit the ability to “feed on radiation”. For example, the aforementioned C. sphaerospermum and W. dermatitidis are widespread soil organisms, and C. neoformans sometimes infect humans, causing infectious cryptococcosis.
Such mushrooms grow quite easily in laboratory conditions, they are easy to manipulate. And due to their ability to populate areas with high contamination, they can become a convenient tool for the disposal of radioactive waste. Today, such rubbish - for example, old overalls - is usually pressed and rolled up for storage until unstable nuclides are naturally depleted. It is possible that mushrooms that can survive on high-energy radiation will speed up this process at times.
In 2016, melanized mushrooms collected near the Chernobyl nuclear power plant were sent into space. Even with all the shielding taken into account, the usual radiation levels on the ISS are 50 to 80 times higher than background radiation near the Earth's surface, providing conditions for the growth of such cells. The samples spent about two weeks in orbit before being returned to allow scientists to investigate how microgravity affected them. Perhaps someday mushrooms will have to live like this from generation to generation.
The energy of the star's radiation rapidly weakens as it moves to the periphery of the solar system, but cosmic radiation is present in the most distant outskirts. In theory, the melanin of fungal cells could be used to produce biomass or synthesize complex molecules that would be required during long-distance manned missions. It is likely that, in addition to green and lush greenhouses, the spaceship of the future will have to arrange another one - the most distant one, which will be overgrown with useful black mold, capable of absorbing radiation energy.