Chernobyl Worms Show No Genetic Radiation Damage

Microscopic worms that spend their lives in the intensely radioactive Chernobyl Exclusion Zone (CEZ) seem to remain entirely untouched by radiation-related harm.

Nematodes gathered in the region showed no evidence of genome damage, despite expectations for creatures surviving in such a hazardous setting. Published earlier this year, the findings do not mean the CEZ is safe, the researchers say. Instead, they indicate that these worms are robust and can adapt skilfully to conditions that would be hostile to many other species.

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

Chernobyl Exclusion Zone and its radioactive wildlife

After a reactor exploded at the Chernobyl Nuclear Power Plant in April 1986, the surrounding area and the nearby Ukrainian town of Pripyat were placed strictly out of bounds to anyone lacking government authorisation. Radioactive material released into the environment exposes living organisms to dangerously high levels of ionising radiation, substantially increasing the likelihood of mutations, cancer and death.

It will take thousands of years before ‘Chornobyl’, the Ukrainian spelling, is once again suitable for human residents. Most people understand this and keep away. Animals, however, cannot know to avoid the area: they roam where they choose, and the exclusion zone has consequently become an unusual radioactive animal sanctuary covering 2,600 square kilometres (1,000 square miles).

Studies of animals living there have identified distinct genetic differences compared with animals 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 collected from the CEZ

One approach to answering this question is to examine nematodes, microscopic roundworms found in numerous environments, including inside the bodies of other organisms. Nematodes can be exceptionally resilient: several instances have documented them reviving after spending thousands of years frozen in permafrost.

Their genomes are uncomplicated and their lifespans brief, allowing researchers to investigate several generations over a short period. These characteristics make them valuable model organisms for examining subjects ranging from biological development to DNA repair and responses to toxins. For that reason, Tintori and her team searched Chornobyl for soil-dwelling nematodes of the species Oschieus tipulae.

Using Geiger counters to record ambient radiation and protective suits to guard against radioactive dust, they gathered hundreds of nematodes from decaying fruit, leaf litter and CEZ soil. Nearly 300 of the collected worms were grown in the laboratory, with 15 O. tipulae specimens selected for genome sequencing.

The resulting genomes were compared with sequenced genomes from five O. tipulae specimens collected elsewhere worldwide: the Philippines, Germany, the United States, Mauritius and Australia.

Genome results and DNA-damage tolerance

The CEZ worms were generally more genetically alike than they were to worms from other locations. Across the complete 20-strain sample, genetic distance matched geographical distance. However, there were no indications of DNA damage caused by the radioactive environment.

After closely examining the worms’ genomes, the researchers found no signs of the major chromosomal rearrangements anticipated in a mutagenic setting. Nor did they identify any relationship between each worm’s mutation rate and the level of ambient radiation at its collection site.

Lastly, the team tested descendants from each of the 20 worm strains to establish how effectively the population withstands DNA damage. Every lineage displayed its own tolerance level, but this also showed no connection with the ambient radiation experienced by its ancestors.

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

What they did uncover, however, could assist researchers seeking to understand why some 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.