“Hulk”-like microorganisms in soil can survive high levels of gamma radiation

“Hulk”-like microorganisms in soil can survive high levels of gamma radiation

In the Marvel Universe, Bruce Banner exposed his body to high doses of gamma radiation during an experiment in his lab. The gamma radiation deformed Bruce’s DNA, so whenever he became angry, he could turn into the Hulk.

In the real world, gamma radiation is a type of high energy radiation that is extremely dangerous to humans. This type of radiation occurs naturally in certain elements, such as Radium-226, Uranium-236, or Thorium-229. Because of this radiation, these elements are too dangerous and unstable to be used in everyday applications. Some radioactive elements can also be synthesized in nuclear reactors, like Cobalt-60. These types of gamma radiation do interact with our DNA, but rather than transforming into our own version of the Hulk, our DNA is mutated or destroyed. In cases of extreme exposure, this could lead to illnesses such as cancer or death.

While humans are extremely susceptible to the harmful effects of gamma radiation, there are actually some small microorganisms (bacteria, archaea, fungi – “microbes”), out there that have evolved to be resistant to radiation. The unit Grayis the absorption of one joule of radiation energy per kilogram of matter. To make this relatable, the human body can only withstand about 3 Grays (Gy) of radiation before dying. Some microbes, like the Deinococcus and Thermococcus groups, can repair their DNA and even switch metabolisms under the harsh conditions to survive up to ten thousand times that amount.

Ionizing radiation is a type of high energy radiation that carries enough energy to remove electrons from atoms or molecules. Scientists from South Korea, Nigeria, USA, and China wanted to know how ionizing radiation, such as gamma radiation, would impact microorganisms living in soil. The scientists collected 15 soil samples from the campus of Seoul National University, where there is a cool humid temperate climate. They brought the soils back to the lab and subjected the samples to 5 treatments. They had a pre-treatment set to test the soil samples before any radiation was applied, and a control set that would never receive radiation exposure. They then exposed the soil samples to weekly doses of either low (100 Gray/hour/week), medium (1,000 Gray/hour/week), or high (3,000 Gray/hour/week) levels of Cobalt-60 gamma radiation. After the six weeks of radiation, they extracted DNA from soil in all the tests, and used a technique called metagenomics to compare the organisms still around in the low, medium, and high radiation soils.

With an increase in the dose of radiation, bacterial communities decreased in diversity, but fungi and algae actually increased in diversity. The scientists suggested that while the weekly doses of radiation eliminated diversity in some groups (bacteria), it may have given space for the survivors (fungi and algae) to grow and prosper. Since fungi can feed off of the cellular material left behind, they could grow quickly and take the place of bacteria. Similarly, the scientists examined the diversity of genes actively used by microbes (“active genes”) within these soils, and found that genes active for bacteria, fungi, and algae had all increased. Since the radiation exposure was a true test of these organisms’ limits, it makes sense that they would pull out every tool they had to try to survive.

Since only one soil type was tested in this study, future work will need to test many other soil types to see if there are also radiation resistant organisms present. This would allow a full understanding of the organisms capable of tolerating high levels of radiation.

A promising find from this study was that a few groups really stood out to be radiation-tolerant. This included Chloroflexi (bacteria), Chytridiomycota (fungi), and Nanoarchaeota (archaea). In the future, more tests can be done to see just how much radiation they can withstand. Since exposure to intense radiation is one limiting factor to human space exploration, scientists can learn more about how these microbes repair their cells and survive such high doses to get an idea of how humans would need to “adapt” to accommodate such high doses of radiation.

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