Scientists of the Molecular Cell Genetics Sector of the Laboratory of Nuclear Problems at JINR have discovered living organisms – several species of fungi – near the centre of the IBR-2 Research Reactor, with background radiation per day 16 times higher than the lethal radiation dose for humans. The scientific team is carrying out a study to find out what genetic mechanisms allowed fungi to adapt to surviving in such harsh conditions. In the future, another search for representatives of this and other kingdoms of life forms will be conducted at the reactor. What makes the study unique is that specialists managed to develop a sampling system to collect samples as close as possible to the very “heart” of the nuclear reactor and check whether organisms live there or not.

Radioresistant fungi after several months of growth in Petri dishes

Studies of the extreme radioresistance of tardigrades – animals able to withstand extreme physico-chemical stresses – are underway at DLNP since 2019. DLNP Director Evgeny Yakushev suggested paying additional attention to searching for radiation-resistant organisms near the IBR-2 Reactor. Unlike at particle accelerators, a significant radiation background is constantly present in the IBR-2 zone, since even when the reactor is shut down, nuclear fuel, plutonium dioxide, continuously decays.

“There is always background radiation near the IBR-2 Reactor: this year, when the reactor was inactive, it was about 160 Grays per day. There are no such dose rates anywhere in nature. For comparison, a dose of 10 Grays is fatal for humans,” Head of the DLNP JINR Molecular Cell Genetics Sector Elena Kravchenko said. At the same time, there’s an opportunity to get almost to the very centre of the IBR-2 Reactor, where the fuel elements are located. The channels of various research facilities are near it, with some channels located just outside the wall of the reactor’s core. Employees of the Sector of the New Neutron Source and Complex of Moderators of the Laboratory of Neutron Physics at JINR gave the DLNP colleagues the opportunity to take biological samples from the area closest to the reactor in the IBR-2 channel 3, where electronics and various materials are tested for radiation resistance.

Automatic sampling box

For the pilot sampling experiment, Head of the DLNP JINR Astrophysical Research Sector Artur Borodin manufactured and programmed an automatic airtight box containing a Petri dish with a nutrient medium. The closed box, presterilised in the laboratory, was delivered to the far side of the channel 3. After reaching the point closest to the reactor (less than half a meter from the core), the box automatically opened for 24 hours, then closed again, and was transported back.

This sampling method is effective for fungi and bacteria, since their spores and cells can enter the laboratory container with a nutrient medium from the air at the sampling point. The dishes that were transported to the IBR-2 zone were filled with a sterile nutrient medium suitable for the growth and development of fungi of certain species, as DLNP JINR geneticists had decided to start the research on organisms that are more complex than bacteria. The presence of animals in the studied area is unlikely, but tardigrades could theoretically survive in these conditions.

“To our delight, seven types of mushrooms grew on the cup in the first experiment,” Elena Kravchenko said. The fungi grew almost immediately from active, viable cells: the next day, the scientists already had small colonies. After being moved from the harsh environment to the normal one, fungi with increased radiation resistance continue their normal life and reproduction cycles. It is important to note that they are nonpathogenic and do not pose a danger to humans.

Radioresistant fungi after sampling at the IBR-2

“We separated individual fungal representatives, conducted a simple species identification by sequencing a small piece of a gene encoding 18S RNA, and found out that penicillium, aureobazidium, pyronema, and others came from the IBR-2. So far, we conducted genome-wide sequencing of one of the seven species: we read its entire genome and assembled its sequence. Analysis is currently underway, and we are placing the sequenced species on the phylogenetic tree of all living organisms. If it doesn’t match anything, it may be a new species,” Elena Kravchenko said.

The main problem that the employees of the Molecular Cell Genetics Sector is solving is figuring out how living organisms adapt to extremely high doses of radiation. To do this, it is necessary to identify genes in the genome and understand how they are arranged. After the genes in the fungal genome are identified, scientists will conduct experiments with all the detected species: a control Petri dish with a certain species will be exposed to normal radiation, while the other cup will be exposed to high radiation doses. Geneticists will then isolate RNA from fungal cells from control and irradiated dishes and analyse which genes are activated in response to radiation.

“Once we know which genes reacted, we can determine what adaptation mechanisms the body managed to develop during natural selection and living in harsh conditions: for example, highly effective DNA repair or DNA protection systems,” Elena Kravchenko explained. In addition, the scientists plan to send Petri dishes with nutrient media for other organisms to the IBR-2 Reactor area before and after the reactor is on.

Elena Kravchenko notes that in addition to the fundamental scientific importance of such studies, the results will be of use for planning long-range human space flights in the future. For example, it will be possible to modify agricultural crops in order to grow them on a spacecraft during flight. Besides, radiation-resistant organisms will help clean up radionuclide-contaminated areas on Earth, and their radioprotection mechanisms will help protect healthy tissues around a cancerous tumour when it is exposed.

Head of the DLNP JINR Molecular Cell Genetics Sector Elena Kravchenko

Studying the radioresistance of fungi found in the IBR-2 Reactor area will take the sector’s scientists several years. The obtained results will be unique, as such experiments have not yet been conducted anywhere in the world: it is almost impossible to get so close to the centre of nuclear decay at a nuclear power plant with research equipment, and the scientific infrastructure of the IBR-2 allows for this.

The increased radiation background in the IBR-2 area affected the living organisms trapped there for years, long before sampling, so the constant effect of the high background radiation allowed for the survival of only the organisms whose genome had unique inherited mechanisms of radioresistance and adaptation.

“Having just the circumstances, facilities, people, and goals for such a study to be conducted only here, at JINR, was great luck,” Elena Kravchenko concludes.

“Researchers are actively studying ecosystems that formed years after radiation accidents happened in places such as Fukushima or Chernobyl. However, the background radiation is several orders of magnitude lower in zones available to scientists than in the area of the IBR-2 Reactor. And we can already say that the species of organisms found there are different from those at the IBR-2,”a junior researcher at the sector Mikhail Zarubin says.

A junior researcher at the DLNP JINR Molecular Cell Genetics Sector Mikhail Zarubin