The International Space Station May Need More Microbes to Keep Astronauts Healthy

The International Space Station May Need More Microbes to Keep Astronauts Healthy

By Allison Parshall edited by Lee Billings

For almost a quarter-century, humans have continuously occupied what is arguably our most isolated habitat ever: the International Space Station, or ISS. Perched in the near vacuum of low-Earth orbit, it’s been home to some 270 people and a variety of animal guests—plus the microbes that hitched a ride to space on the bodies of those residents.

There these uninvited microbial guests have been evolving. Bacteria adapt to cosmic radiation with new ways to repair their DNA. Some become resistant to antibiotics and sterilizing agents or develop other changes that make them more likely to cause disease.

“To take care of us humans, we have to take care of our human microbes. And that’s going to be a very interesting challenge.” —Martin Blaser, microbiologist

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“This is such an extreme environment,” says Rodolfo Salido, a bioengineer at the University of California, San Diego. And the microbes that inhabit it can directly affect astronaut health. To map the space station’s microbial world, Salido and his colleagues sent swabs up to space, where astronauts sampled hundreds of surfaces. Their resulting three-dimensional map of the ISS’s microbial diversity, published on Thursday in the journal Cell, shows that this orbital habitat lacks many types of bacterial life that humans normally encounter and that may be important for our well-being. To stay healthy on future long-term off-world forays, the researchers suggest, we may need a little more help from our microbial friends.

“To take care of us humans, we have to take care of our human microbes. And that’s going to be a very interesting challenge” in space travel, says Martin Blaser, a microbiologist at Rutgers University, who was not involved in the new study.

In December 2020 Salido and his colleagues collaborated with NASA’s Jet Propulsion Laboratory to launch about 1,000 sterilized sampling devices to the ISS. The team had redesigned the devices to work in space: as an Earth-bound scientist, Salido had learned a lot from a visit to a replica of the ISS in Houston, where astronaut Michael Barratt pointed out that the researchers’ normal sampling swabs were far too large and flammable to fly.

After the redesigned swabs arrived at the ISS, astronaut and microbiologist Kathleen Rubins and other crew members spent a total of 24 hours swabbing surfaces across the U.S. portion of the space station. They took a total of 803 swabs, which were returned to Earth in October 2021. The researchers then analyzed the samples to identify the genes and chemical by-products (and therefore the types of microbial species) that were present. They found that most bacteria on the ISS were those that live on our skin, such as species of Staphylococcus. And importantly, there was very little of the bacteria we normally encounter in Earth’s soil and water.

In many ways, this situation is “like in any building that you’ve ever been in,” Blaser says. “We’re shedding microbes off our skin all the time,” and there are more of them in buildings with low air flow than the microbes in your backyard. Some indoor environments are more microbially skewed than others. In previous research Blaser and his colleagues sampled rural and urban homes in South American locations ranging from a small village in the remote Amazon to the bustling metropolis of Manaus, Brazil. They found that as our living spaces become more isolated from the natural environment, this also depletes the microbes that are usually present in those places.

But the ISS is no typical location. In their new study, the researchers compared their samples from the space station with those they took from homes in South America, as well as additional samples obtained from other terrestrial environments such as hospitals. They found the ISS was on the extreme low end of microbial diversity. One comparison in particular stood out to Haoqi Nina Zhao, an environmental chemist at U.C. San Diego and co-lead author of the study: “The ‘home’ on Earth that looks most similar to the [ISS] was an isolation dormitory used during COVID 19,” she says.

How much this microbially skewed habitat might impact astronaut health is still a matter of speculation. The researchers hypothesize that it could contribute to the rashes and immune dysfunction that astronauts sometimes experience. As we move into more artificial environments, whether on Earth or in space, “we’re breaking our relationship … with the microbial exposures that we evolved to have,” Salido says. “And our immune systems haven’t [yet] learned how to deal with that.”

While some evidence does link low microbial diversity to increased risk of some types of immune system dysfunction, such research usually involves children and the microbes they’re exposed to as their own microbiome develops, not healthy adult astronauts who are temporarily living in space, Blaser says. That would change, however, if our species were to establish longer-term settlements beyond Earth.

“That’s what I’d want to know: How do those babies’ microbes evolve in that kind of condition?” Blaser says. “That’s going to be a really important question for the future of humankind if we’re going to colonize away from Earth.”

In this spacefaring future, we might have to intentionally take some of our old microbial partners with us, nurturing them while still keeping less desirable microorganisms in check. Instead of chemical disinfectants, which can drive antimicrobial resistance, the authors suggest that future research can focus on probiotic-based sanitation, which introduces harmless bacteria to outcompete the potentially harmful ones.

And though some indoor environments might lack important microbes, the answer isn’t to avoid basic hygiene measures, either. “It’s not about avoiding being hygienic,” Salido says. Going forward, it’s about developing ways that our built environments can “include the microbial symbionts, or the microbial friends, that we evolved with.”