Extremophiles On Mars Could Survive For Hundreds of Millions of Years

One of Earth's toughest microbes could survive on Mars, lying dormant beneath the surface, for 280 million years, new research has shown. The findings increase the probability that microbial life could still exist on the Red Planet. Space.com reports: Deinococcus radiodurans, nicknamed "Conan the Bacterium," is one of the world's toughest microbes, capable of surviving in radiation strong enough to kill any other known life-form. Experiments have now shown that if Conan the Bacterium or a similar microbe existed on Mars, it could survive 33 feet (10 meters) beneath the surface, frozen and dried out, for 280 million years. In a study led by Michael Daly, who is a professor of pathology at Uniformed Services University of the Health Sciences in Maryland and a member of the National Academies' Committee on Planetary Protection, scientists tested half a dozen microbes and fungi -- all "extremophiles" able to live in environments where other organisms die -- to see how long they could survive in an environment that simulated the mid-latitudes of Mars. During the experiments, organisms faced temperatures as low as minus 80 degrees Fahrenheit (minus 63 degrees Celsius) and exposure to ultraviolet light, gamma rays and high-energy protons mimicking the constant bombardment of Mars by solar ultraviolet light and cosmic radiation sleeting down from space. After the bacteria and fungi had been exposed to various radiation levels in the experiment, Daly's team measured how much manganese antioxidants had accumulated in the cells of the microbes. Manganese antioxidants form as a result of radiation exposure, and the more that form, the more radiation the microbes can resist. Conan the Bacterium was the clear winner. The researchers found that Conan the Bacterium could absorb as much as 28,000 times more radiation than what a human can survive. This measurement allowed Daly's team to estimate how long the microbe could survive at different depths on Mars. Previous experiments, in which Conan the Bacterium had been suspended in liquid water and subjected to radiation like that found on Mars, had indicated that the microbe could survive below the surface of Mars for 1.2 million years. However, the new tests, in which the microbe was frozen and dried out to mimic the cold and dry conditions on Mars, suggested that Conan the Bacterium would be able to survive 280 million years on Mars if buried at a depth of 33 feet. This lifespan is reduced to 1.5 million years if buried just 4 inches (10 centimeters) below the surface, and just a few hours on the surface, which is bathed in ultraviolet light. [...] The research also determined why Conan the Bacterium is so resistant to radiation. The scientists found that chromosomes and plasmids, which carry genetic information, in the microbe's cells are linked together, which keeps these structures aligned and prevents irradiated cells from breaking down until they can be repaired. "Although Deinococcus radiodurans buried in the Martian subsurface could not survive dormant for the estimated 2 to 2.5 billion years since flowing water disappeared on Mars, such Martian environments are regularly altered and melted by meteorite impacts," he said in a statement. "We suggest that periodic melting could allow intermittent repopulation and dispersal." The findings were detailed in the journal Astrobiology.

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