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The bacterial species Deinococcus radiodurans is a super-extremophile that can survive anything from extreme temperatures and radiation to the pressure of an asteroid impact. When a team of researchers tested just how much pressure the bacterium could withstand by simulating an asteroid impact, they found that its cell membranes are tough enough to make it through.This suggests that life-forms flung into space by violent impacts on other worlds may have colonized planets and moons over billions of years.
Whether extraterrestrial life exists is still an open question, but some Earth organisms might as well be aliens. There are microbes that can tolerate conditions in space that would obliterate just about everything else that lives on our planet. Some of those microbes could even survive an asteroid impact that blasts them into space from the surface of a planet like Mars.
Deinococcus radiodurans earned the nickname “Conan the Bacterium” for a reason. This species of bacteria has already proven it can live through crushing pressure, searing heat, punishing cold, acid, oxidation, desiccation, the vacuum of space, and radiation that is beyond intense. This is no ordinary extremophile. As a polyextremophile, what it can endure has almost no limits. That’s why a team of researchers led by mechanical engineers Lily Zhao and K.T. Ramesh from Johns Hopkins University decided to see just how much it could take by simulating a Martian impact in their lab. Spoiler alert: more than half of the bacteria survived.
“Our results suggested that microorganisms can survive much more extreme conditions than previously thought, potentially surviving conditions that result in the formation of ejecta that can move across planetary systems,” they said in a study recently published in the journal PNAS Nexus.
Surviving an asteroid impact is more than just an unbelievable feat—it has potentially world-changing consequences. If microbes can make it out alive from under a hunk of asteroid slamming into them at speeds that generate pressures of up to 3 gigapascals (which is about 435,113 pounds per square inch, or 30,000 times the atmospheric pressure on Earth), it might mean there are life-forms out there that can trek from one planet to another by hitching a ride on space rocks. The researchers recreated conditions of an impact on Mars by placing D. radiodurans between two steel plates and smashing a third plate into them. It wasn’t until they reached pressures of 2.4 gigapascals that any of the bacteria started showing signs of stress. So where do they get their superpowers?
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The almost unearthly endurance of D. radiodurans originates in its genes. Extreme pressure will crush most microorganisms—rupturing cell membranes, causing oxidative stress, messing with the transport of electrons and proteins, and dissociating ribosomes, which are needed to synthesize proteins. But Deinococcus radiodurans is virtually immune to these effects, thanks to its molecular response to dynamic pressure. Previously, extremophilic bacterial species, such as Shewanella oneidensis, have only been tested under extreme hydrostatic pressure. D. radiodurans resists otherwise deadly conditions because of an antioxidant system that prevents oxidative damage to its proteins and repairs DNA. Enzymes that behave like sensors trigger repair mechanisms that allow it to rapidly reassemble its genome.
Another important factor in why the bacterium is so tough is its cell membrane. But the membrane’s toughness doesn’t stem from thickness—other microbes that are piezophilic (meaning they thrive in high-pressure habitats like deep sediments and the bottom of the ocean) actually have thicker membranes. Instead, the crystalline arrangement of proteins in the membrane of D. radiodurans is what helps it resist impact stress: its cell membranes held up through increasing levels of pressure applied by the research team. It’s only at 2.4 gigapascals that its membranes began to rupture. Zhao and Ramesh theorize that that this occurred as a result of superfast unloading of pressure—when the strain energy stored in the cell is released, it can break the membrane. Yet 60% of the bacteria still survived these extraordinary pressure levels.
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This experiment also gives the lithopanspermia hypothesis more of a backbone. If life can traverse space on flying rocks, occasionally crashing into other celestial bodies, then it might be lurking somewhere unexpected. Simulations showed that impacts to Earth and Mars could have transferred ejected material among terrestrial planets and even the moons of Jupiter and Saturn. The researchers think this phenomenon happened most frequently during the Late Heavy Bombardment, which threw off the orbits of our solar system’s giant planets and caused chaos in the asteroid belt. What are now icy moons such as Europa were mostly covered in liquid oceans that meteorites and their tiny hitchhikers could pass right through.
“Transfer of life to these moons cannot be ruled out, and searches for life on these objects should keep in mind the necessity of determining whether life arose independently or descended from common ancestors to Earth life,” they said. “Any life found there cannot be assumed to be of independent origin.”
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Elizabeth Rayne is a creature who writes. Her work has appeared in Popular Mechanics, Ars Technica, SYFY WIRE, Space.com, Live Science, Den of Geek, Forbidden Futures and Collective Tales. She lurks right outside New York City with her parrot, Lestat. When not writing, she can be found drawing, playing the piano or shapeshifting.