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Mold growing on the inside of the International Space Station, where exercise clothing was hung to dry.


Space station mold survives 200 times the radiation dose that would kill a human

BELLEVUE, WASHINGTON—As anyone who’s ever had a mold infestation knows, the fungi can be very hard to kill. It turns out mold may also be highly resistant to the harsh conditions of outer space. Its spores can survive doses of radiation 200 times higher than those that would kill a human, researchers reported here today at the Astrobiology Science Conference. Such hardiness could make it difficult to eliminate mold's health risks to astronauts. Mold might also one day threaten other parts of the solar system—with hitchhiking mold spores from Earth.

Astronauts on the International Space Station (ISS) already constantly battle with mold, which grows on the station’s walls and equipment. That mold, of course, is in a protected structure in low-Earth orbit, where radiation doses are low. Outside of the station, doses are higher—and they would be higher still on the hull of a spacecraft going to Mars or beyond.

To find out what might happen to mold there, Marta Cortesão, a microbiologist at the German Aerospace Center (DLR) in Cologne and colleagues beamed x-rays and heavy ions at a common black mold called Aspergillus niger, which is plentiful in the ISS. The researchers fired “stupid amounts” of radiation, Cortesão says—much more than encountered on a Mars-bound spaceship (0.6 gray per year) or on the surface of Mars (0.2 gray per year). The gray is a measure of the amount of absorbed radiation energy.

The researchers discovered that the spores could survive radiation doses of 500 to 1000 gray, depending on which type of radiation they were exposed to. Humans, by contrast, get radiation sickness at doses of 0.5 gray and are killed by 5 gray. Cortesão also found that the spores survived large amounts of high-energy ultraviolet radiation, which is commonly used as a hospital disinfectant and has been proposed for sterilizing the surfaces of spacecraft.

Cortesão cautions that her research focused only on radiation and did not include all aspects of the harsh outer space environment. But, she says, at least one older study suggests that mold spores resist radiation even better in a vacuum. Meanwhile, one thing is certain, she says: “We will have spores with us for sure in our space travels. Fungi have been forgotten for the past 20 or 30 years, but it’s time to go back to them.”

Andrew Schuerger, a microbiologist and Mars astrobiologist at the University of Florida in North Merritt Island, agrees. Most of the focus on keeping Earth’s microorganisms from contaminating other worlds so far has been on bacteria, he says, because the vast bulk of microorganisms on the surfaces of spacecraft has been bacterial. “I really like a presentation like this [that says] ‘Let’s not forget about this other group of microorganisms called fungi,’” he says.

The finding is also important for researchers studying the origin of life, says Paul Mason, an astrobiologist at New Mexico State University in Las Cruces.

That’s because one of the puzzles in origin-of-life research is that Earth seems to have gone from prebiotic all the way to fairly complex microorganisms early in its history—a process that some scientists think required more time than had passed since the planet first became habitable. One idea, Mason says, is that life originated elsewhere, either in our solar system or farther afield. “Now that we know that Earth life can survive in space, it is certainly reasonable to think that it could have arrived on Earth from somewhere else,” he says.