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Space-Bound Humans Bring Fungus Aboard—And the Stowaways Could Cause Trouble

Microscopic life is everywhere, but it could be dangerous for future astronauts bound for Mars

Researchers tested the fungus that grew in this isolated habitat as four people lived in it for a month. (Blachowicz et al / Microbiome)
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Humans settling on Mars will face many challenges—deadly radiation, powerful dust storms, tenuous communication with Earth and more. Now, new research from NASA scientists sheds light on another potentially harmful problem: fungus.

No, there isn't any fungus on Mars, as far as we know; the problem could come from the teeming mycobiome of the human body. "Humans are walking fermenters," says Kasthuri Venkateswaran, a microbiologist with NASA's Jet Propulsion Laboratory. "We carry along at least 10 times more microbial cells [than human cells]."

In our day-to-day lives on Earth, the fungi we live with aren't usually an issue. But in the confined habitat of a spaceship and potentially a Martian settlement, some researchers worry that the microbes that thrive in confined spaces could sicken people or even damage equipment. Venkateswaran, who is a member of NASA's Biotechnology and Planetary Protection Group, is also concerned about human settlers contaminating Mars with our own microbes.

To see how the fungi we carry can change in the isolation of a space habitat, Venkateswaran and his team decided to piggyback on a research project focused on the psychological effects of isolating people together for long periods. Four students were locked in an inflatable habitat in North Dakota with four rooms for a month, allowed out only in spacesuits to conduct simulated missions. All the air entering the enclosure was filtered.

This left mycobiome of the hab untouched by the outside for an entire month, allowing researchers to see how it changed as the simulated astronauts lived their lives. Venkateswaran had the students take fungus samples from each room at the beginning of the experiment and then roughly every 10 days. They were also under strict instructions to thoroughly clean each room once a week.

The results, published this week in the journal Microbiome, showed notable changes during the month of testing. While the overall number of fungi found in the hab decreased, Venkateswaran says, certain fungus species increased substantially. The find confirmed the team's previous work on the microbial changes in confined spaces, suggesting that such isolated environments are susceptible to the minute life riding along with the hab's human inhabitants. 

Venkateswaran is planning future research on the International Space Station and on Earth to look more specifically at what exactly those changes mean, why they happen, and how they could be prevented if they turn out to be harmful. "We have to learn from here and come up with a different cleaning agent that affects these fungi if they are really problematic," he says.

Other researchers caution against extrapolating the data from this latest study too far.  "The study seems well performed, but it would be very interesting to do further experiments to support the purported conclusions." says Jack Gilbert, faculty director of the University of Chicago's Microbiome Center. Gilbert, who was not involved in this research, has extensively studied how microbes and humans have interacted in built environments like homes and hospitals. 

"There is no indication that the observed changes are not safe," he says. Therefore, different cleaning techniques may not be necessary to prevent disease during the long space flight.

"Fungal monitoring may part of 'proper maintenance protocols' but no one knows what is  'proper maintenance,'" says Koichi Makimura, a medical researcher at Japan's Teikyo University who was also not involved in this study.

Makimura, who has studied microbes on the International Space Station, says that fungi research in general has been neglected here on Earth, so it's hard to conclude what this study's results might mean for the health of the humans isolated with these fungi. But one thing is clear—there's no getting rid of them entirely, even in space.

"As we all know," Makimura says, we need to live with microbes."

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