Can a humble bacterium hold the key to surviving cosmic radiation?
The bacterium Deinococcus radiodurans is considered the only organism with the extraordinary ability to restore a shattered genome into thousands of pieces. A team of researchers from France and Croatia, led by Miroslav Radman from the INSERM Institute (France), has uncovered the stages of this recovery process that allow the bacterium to come back to life after enduring extremely high levels of radiation.
The bacterium Deinococcus radiodurans can restore its shattered genome into thousands of pieces.
Researchers from Northwestern University and the Uniformed Services University have clarified how this bacterium protects itself: through a special antioxidant known as MDP. This compound is synthesized from three simple yet highly effective components – manganese ions, phosphates, and a synthetic peptide. When combined, they form a robust defense layer that protects proteins and cells from the ravages of radiation.
According to Professor Michael Daly, a pathology expert at the Uniformed Services University, this molecular structure is viewed as the “secret sauce” of Deinococcus radiodurans. He explains, “The decapeptide interacts sequentially with phosphate and manganese to create a unique trivalent complex, providing extremely effective radiation resistance.”
For decades, the scientific community believed that radiation kills cells primarily by damaging DNA. However, recent research indicates that this is only part of the story. Radiation not only destroys DNA but also severely harms the proteome – the essential protein system of the cell. These proteins perform many critical functions, from repairing DNA damage to regulating metabolic processes. When reactive oxygen species (ROS) are produced by radiation, they directly attack proteins, preventing cells from performing basic functions, even if the DNA remains intact.
Deinococcus radiodurans has developed a unique strategy to tackle this issue. Thanks to manganese-based antioxidants, this bacterium neutralizes ROS before they can damage the proteome. This is a crucial factor that enables it to survive in harsh environments such as cosmic radiation or nuclear reactors.
The bacterium Deinococcus radiodurans was first discovered by an American researcher in 1956 while attempting to sterilize canned beef by exposing it to a very strong gamma radiation beam. He was surprised to note that the bacterium did not die under this level of radiation. The species Deinococcus radiodurans can withstand radiation doses hundreds of times higher than lethal levels.
The genome of Deinococcus radiodurans has a circular structure that can be broken into thousands of pieces. Researchers noted that the cells appeared dead for about an hour and a half. However, three hours after being irradiated, its DNA was reassembled as before.
The bacterium Deinococcus radiodurans.
First discovered in a can of meat, D. radiodurans survived and thrived after a year of being placed on a specially designed platform outside the pressurized module of the International Space Station (ISS).
The dehydrated bacterial cells were sent to the ISS, placed in the Exposed Facility, a platform continually exposed to the space environment. In this case, the cells were located behind glass that could block UV rays at wavelengths below 190 nanometers. The research team from Austria, Japan, and Germany published their findings in the journal Microbiome.
“The results presented in this study may enhance awareness of protective measures on other planets. For example, the Martian atmosphere absorbs UV radiation below 190 – 200 nm. To simulate this condition, the experiment we set up on the ISS included a silicon dioxide glass window”, the research team stated.
This is not the longest duration D. radiodurans has survived in space. However, the research team was not aiming to set a world record but rather to explore what enables D. radiodurans to thrive in such extreme conditions. After a year of exposing the samples to radiation, freezing temperatures, extreme heat, and microgravity, the researchers brought this bacterium back to Earth, hydrating both the samples tested on Earth and those in Low Earth Orbit (LEO).
The survival rate of the bacteria in the LEO samples was significantly lower than that of the Earth control samples, but the surviving bacteria appeared to be quite stable, albeit somewhat different from their Earth counterparts. The research team found that the LEO bacteria had small protrusions covering their surfaces. They also activated several self-repair mechanisms. Additionally, certain proteins and mRNA became more abundant.
Scientists do not know exactly why these protrusions form, but they have several hypotheses. The protrusions may serve as a quick response to stress, enhancing the cell’s survival capability by alleviating pressure. Furthermore, the protrusions on the outer membrane may contain proteins important for nutrient uptake, DNA transfer, toxin transport, and density-sensing molecules that promote resistance mechanisms after being in space.
In August 2020, research conducted on the International Space Station (ISS) revealed that the bacterium Deinococcus radiodurans can survive in space for at least three years. Many believe this discovery reinforces the theory of “panspermia” – the hypothesis that life exists throughout the universe and is distributed in various ways.
Anne Kinney, Director of the Origins and Planetary Systems Program at NASA, stated, “We could be the generation that discovers the origins of life. Are we the center of the universe or not?”.
The endurance in harsh environments and subsequent self-repair of Deinococcus radiodurans has become a widespread research target. Biologists hope to harness the superior mechanisms of this bacterium strain to help humans better combat radiation or to process hazardous waste.
To date, scientists have not been able to determine the natural habitat of Deinococcus radiodurans, as it has been found in numerous environments, including in elephant dung and granite in Antarctica.
Decades after its discovery, Deinococcus radiodurans still holds the Guinness World Record for the “toughest bacterium in the world.” It is also regarded as the best-known antibiotic-resistant organism ever discovered.
