The microscopic worms of Chernobyl that resist radiation

Microscopically small worms that live in the highly radioactive environment of the Chernobyl Exclusion Zone (CEZ) appear to be completely free of radiation damage

The nematodes collected in the area showed no signs of damage to their genome, contrary to what would be expected from organisms living in such a dangerous place. The finding does not mean that the ZEC is a safe place, the researchers say, but rather that it is a safe place Worms are hardy and can adapt adeptly to conditions that might be inhospitable to other species.

According to a team of biologists led by Sophia Tintori of New York University, this could provide some insight into DNA repair mechanisms that could one day be adapted for use in human medicine.

The superworms

Since the explosion of a reactor at the Chernobyl nuclear power plant in April 1986, the area and the nearby Ukrainian city of Pripyat have been strictly closed to anyone without government permission. Radioactive materials deposited in the environment expose organisms to extremely dangerous levels of ionizing radiation, significantly increasing the risk of mutations, cancer and death.

It will take thousands of years before “Chornobyl,” as it is spelled in Ukraine, is safe for humans again. Most of us know this and stay away from it. But animals don’t understand that they have to move away. They go wherever they want, and the exclusion zone has now become a strange kind of 2,600 square kilometer radioactive animal sanctuary.

Analyzes of animals that live in the area have shown significant genetic differences from animals that do not live there. However, we still don’t know much about the impact of the disaster on local ecosystems.

“Chernobyl was a tragedy of unimaginable proportions, but we still do not fully understand the impact of the disaster on the local population,” says Tintori. “Has the sudden environmental change selected species, or even individuals within a species, that are naturally more resistant to ionizing radiation?”

One way to answer this question is to study nematodes, microscopic worms that live in various habitats (including the bodies of other organisms). Nematodes can be extremely resistant; There have been several cases of nematodes coming back to life after being frozen in permafrost for thousands of years.

They have simple genomes and short lives, allowing multiple generations to be studied in a short period of time. This makes them excellent model organisms for studying a range of things, from biological development to DNA repair to response to toxins. For this reason, Tintori and his colleagues conducted excavations in Chernobyl to find nematodes of this species Oschieus tipulaewhich normally lives in the ground.

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At the ZEC, they collected hundreds of nematodes from rotting fruit, leaf litter and soil, measured the ambient radiation with Geiger counters and wore protective suits against radioactive dust. The researchers cultured nearly 300 of the collected worms in the laboratory and selected 15 specimens of O. tipulae to sequence their genome.

These sequenced genomes were then compared with the sequenced genomes of five O. tipulae specimens from other parts of the world: the Philippines, Germany, the United States, Mauritius and Australia.

The CEZ worms were mostly genetically more similar to each other than to the other worms, and the genetic distance corresponded to the geographical distance of the entire sample of 20 strains. However, there was no evidence of DNA damage due to the radiation environment.

The team carefully analyzed the worms’ genome and found no evidence of the large-scale chromosomal rearrangements that would be expected in a mutagenic environment. They also found no connection between the mutation rate of the worms and the intensity of environmental radiation at the respective place of origin.

Finally, they tested the offspring of each of the 20 worm strains to determine the population’s level of tolerance to DNA damage. Although each lineage had different levels of tolerance, this did not correlate with the environmental radiation their ancestors were exposed to.

The team could only conclude that there is no evidence of a genetic influence of the ZEC environment on the genomes of O. tipulae. And what they found could help researchers figure out why some people are more susceptible to cancer than others.

“Now that we know which O. tipulae strains are more sensitive or tolerant to DNA damage, we can use them to study why some individuals suffer from the effects of carcinogens more often than others,” says Tintari. “If we think about how individuals respond differently to DNA-damaging agents in the environment, we can get a clear picture of our own risk factors.”

REFERENCE

Environmental radiation exposure at Chernobyl did not systematically affect the genomes or chemical mutagen tolerance phenotypes of local worms

Photo: Nematodes collected in the Chernobyl exclusion zone. (Sophia Tintori)

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