Microscopic worms living in the highly radioactive environment of the Chernobyl Exclusion Zone (CEZ) appear to do so completely unscathed by the radiation.
Nematodes collected from the area showed no signs of damage to their genome, contrary to what might be expected for organisms living in such a dangerous place. The finding, published earlier this year, does not suggest that CEZ is safe, the researchers said SAYbut on the contrary worms are resilient and able to adeptly adapt to conditions that may be inhospitable to other species.
This, says a team of biologists led by New York University’s Sophia Tintori, may provide some insights into DNA repair mechanisms that may one day be adapted for use in human medicine.
Since the explosion of a reactor at the Chernobyl nuclear power plant in April 1986, the area around it and the nearby city of Pripyat in Ukraine have been strictly off-limits to anyone without government approval. Radioactive materials deposited in the environment expose organisms to extremely unsafe levels of ionizing radiation, greatly increasing the risk of mutation, cancer, and death.
It will be thousands of years before ‘Chornobyl’, as it is written in Ukraine, is safe for human habitation again. Most of us know this and stay clear accordingly. But animals… well, they don’t understand staying away. They go where they want, and the exclusion zone has since become a strange sort of radioactive animal sanctuary, 2,600 square kilometers (1,000 square miles).
Tests of animals living in the region have shown clear genetic differences from animals that don’t. But there is still much we don’t know about the effects of the disaster on local ecosystems.
“Chornobyl was a tragedy of incomprehensible proportions, but we still do not have a good understanding of the effects of the disaster on the local population,” Tintori said at the time. “Did sudden environmental change select for species, or even individuals within a species, that are naturally more resistant to ionizing radiation?”
One way to gain insight into this question is to look at nematodes—microscopic roundworms that live in a variety of habitats (including the bodies of other organisms). Nematodes can be extremely persistent; there have been numerous cases of nematodes reawakening after thousands of years frozen in permafrost.
They have simple genomes and live short lives, meaning that multiple generations can be studied in a short space of time. This makes them excellent model organisms for studying a variety of things, from biological development to DNA repair and response to toxins. That’s why Tintori and her colleagues went digging in Chornobyl to find nematodes of the species Oschieus tipulaewhich usually lives on land.
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They collected hundreds of nematodes from rotting fruit, leaf litter and soil at the CEZ, using Geiger counters to measure ambient radiation and wearing protective suits against radioactive dust. The researchers cultured about 300 of their collected worms in a laboratory and selected 15 specimens of O. tipulae for genome sequencing.
These sequenced genomes were then compared to the sequenced genomes of five specimens of O. tipulae from other countries in the world – the Philippines, Germany, the United States, Mauritius and Australia.
CEZ worms were mostly genetically more similar to each other than to other worms, with genetic distance corresponding to geographic distance for the entire 20-strain sample. But signs of DNA damage from the radiation environment were absent.
The team carefully analyzed the worms’ genome and found no evidence of the large-scale chromosomal rearrangements expected from a mutagenic environment. They also found no relationship between the worm’s mutation rate and the strength of the ambient radiation at the location each worm came from.
Finally, they performed tests on the offspring of each of the 20 worm species to determine how well the population tolerates DNA damage. Although each lineage had a different level of tolerance, this also had nothing to do with the ambient radiation their ancestors were exposed to.
The team only concluded that there is no evidence of any genetic influence of the CEZ environment on the genomes of O. tipulae.
And what they found could help researchers try to understand why some people are more susceptible to cancer than others.
“Now that we know what types of O. tipulae are more sensitive or tolerant to DNA damage, we can use these strains to study why different individuals are more likely than others to suffer from 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 get a clearer picture of our own risk factors.”
The research was published in Proceedings of the National Academy of Sciences.
An earlier version of this article was published in March 2024.