Chernobyl Exclusion Zone Nematodes Show No Radiation Damage

Microscopic worms that spend their entire lives within the intensely radioactive Chernobyl Exclusion Zone (CEZ) seem to remain entirely unaffected by radiation damage.

Nematodes gathered in the region displayed no evidence of harm to their genomes, despite the expectations for organisms inhabiting such a hazardous setting. Published earlier this year, the findings do not mean the CEZ is safe, the researchers stress. Instead, they indicate that these worms are robust and can skilfully adjust to conditions that would be unsuitable for many other species.

According to a group of biologists headed by Sophia Tintori of New York University, the work may provide clues about DNA-repair processes that could eventually be adapted for human medicine.

Chernobyl Exclusion Zone: a radioactive wildlife refuge

Following the April 1986 reactor explosion at the Chernobyl Nuclear Power Plant, the surrounding area and the nearby Ukrainian town of Pripyat were placed under strict restrictions, accessible only with government permission. Radioactive material released into the environment subjects living organisms to dangerously high doses of ionising radiation, substantially increasing the likelihood of mutations, cancer and death.

It will take thousands of years before ‘Chornobyl’-the Ukrainian spelling-can once again be safely inhabited by people. Most of us understand this and keep our distance. Animals, however, do not know that they should avoid it. They roam where they please, and the exclusion zone has consequently become an unusual radioactive animal sanctuary covering 2,600 square kilometres (1,000 square miles).

Research on animals living there has identified distinct genetic differences from those in populations elsewhere. Yet much remains unknown about how the disaster has affected local ecosystems.

"Chornobyl was a tragedy of incomprehensible scale, but we still don't have a great grasp on the effects of the disaster on local populations," Tintori said at the time. "Did the sudden environmental shift select for species, or even individuals within a species, that are naturally more resistant to ionizing radiation?"

Nematodes from Chornobyl and DNA repair

One approach to investigating that question is through nematodes: microscopic roundworms found in many environments, including inside the bodies of other organisms. Nematodes can be exceptionally resilient. In several instances, they have revived after spending thousands of years frozen in permafrost.

Their genomes are uncomplicated and their lifespans brief, allowing researchers to examine numerous generations over a relatively short period. These qualities make them valuable model organisms for research into subjects ranging from biological development to DNA repair and responses to toxins. For this reason, Tintori and her team searched in Chornobyl for soil-dwelling nematodes of the species Oschieus tipulae.

Using Geiger counters to record background radiation and protective suits to guard against radioactive dust, the researchers collected hundreds of nematodes from soil, leaf litter and decaying fruit across the CEZ. In the laboratory, they cultured almost 300 of the collected worms and chose 15 O. tipulae specimens for genome sequencing.

The resulting sequences were compared with genomes from five O. tipulae specimens collected in other parts of the world: Australia, Germany, Mauritius, the Philippines and the United States.

No detectable radiation damage in O. tipulae genomes

For the full sample of 20 strains, the CEZ worms were generally more genetically alike than they were to worms from elsewhere, while genetic distance matched geographical distance. However, there was no sign of DNA damage attributable to the radioactive environment.

After closely examining the worms’ genomes, the researchers found no indication of the large chromosomal rearrangements that would be anticipated in a mutagenic setting. Nor did they identify a relationship between each worm’s mutation rate and the level of background radiation where it originated.

Lastly, the team tested descendants from each of the 20 worm strains to establish how effectively the population withstands DNA damage. Every lineage showed a distinct level of tolerance, but this likewise bore no relation to the background radiation their ancestors had encountered.

The researchers could therefore only conclude that the CEZ environment has had no detectable genetic effect on the genomes of O. tipulae.

What they did uncover, however, may assist researchers seeking to understand why certain people are more vulnerable to cancer than others.

"Now that we know which strains of O. tipulae are more sensitive or more tolerant to DNA damage, we can use these strains to study why different individuals are more likely than others to suffer the effects of carcinogens," Tintari said.

"Thinking about how individuals respond differently to DNA-damaging agents in the environment is something that will help us have a clear vision of our own risk factors."

The study was published in the Proceedings of the National Academy of Sciences.

An earlier version of this article was published in March 2024.