For the Sake of Astronaut Health, Should we Make the ISS Dirtier?

There are several well-documented health risks that come from spending extended periods in microgravity, including muscle atrophy, bone density loss, and changes to organ function and health. In addition, astronauts have reported symptoms of immune dysfunction, including skin rashes and other inflammatory conditions. According to a new study, these issues could be due to the extremely sterile environment inside spacecraft and the International Space Station (ISS). Their results suggest that more microbes could help improve human health in space.

The study was led by Rodolfo A. Salido and Haoqi Nina Zhao, a bioengineer and an environmental analytical chemist at the University of California San Diego (UCSD), respectively. They were joined by researchers from multiple UCSD programs and centers, the University of Denver, the Chiba University-UC San Diego Center for Mucosal Immunology Allergy and Vaccines (cMAV), Space Research Within Reach, the Baylor College Center for Space Medicine, the Blue Marble Space Institute of Science (BMSIS), the Biotechnology and Planetary Protection Group at NASA JPL, and the Astronaut Office at NASA Johnson.

The study was a collaborative effort with astronauts aboard the ISS, who swabbed 803 different surfaces – 100 times that of previous surveys – to get a census of microbes aboard the station. The researchers identified which bacterial species and chemicals were present in each sample and created three-dimensional maps to illustrate where each of them was found and how they might be interacting. Their results indicate that the ISS has a much lower diversity of microbes compared to human-built environments on Earth.

NASA astronaut Catherine (Cady) Coleman, Expedition 26 flight engineer, is pictured with a stowage container and its contents in the Harmony node of the International Space Station. Credit: NASA

Overall, the team found that chemicals from cleaning products and disinfectants were ubiquitously throughout the station and that astronauts mostly introduce microbes aboard the ISS through shed human skin cells. They also found that different modules hosted different microbial communities and chemical signatures based on the module’s use. For example, dining and food preparation areas contained more food-related microbes, whereas the ISS’s space toilet contained more urine- and fecal matter-related microbes and bioproducts of metabolism (metabolites).

“We noticed that the abundance of disinfectant on the surface of the International Space Station is highly correlated with the microbiome diversity at different locations on the space station,” said Zhao in a Cell Press release. These results suggest that more microbes from Earth could help improve astronaut health. Said Salido:

“Future built environments, including space stations, could benefit from intentionally fostering diverse microbial communities that better mimic the natural microbial exposures experienced on Earth, rather than relying on highly sanitized spaces. If we really want life to thrive outside Earth, we can’t just take a small branch of the tree of life and launch it into space and hope that it will work out. We need to start thinking about what other beneficial companions we should be sending with these astronauts to help them develop ecosystems that will be sustainable and beneficial for all.” 

The team found that microbial communities were less diverse aboard the ISS than most places on Earth, except where urban, industrialized, and isolated environments (i.e., hospitals) were concerned. They further found that ISS surfaces lacked free-living environmental microbes usually found in soil and water. Similar to the well-documented benefits gardening has for the human immune system, the researchers conclude that incorporating these microbes and their substrates into the ISS could improve astronaut health without sacrificing hygiene.

Astronauts on the International Space Station experience an orbital reboost. Credit: NASA/ESA

“There’s a big difference between exposure to healthy soil from gardening versus stewing in our own filth, which is kind of what happens if we’re in a strictly enclosed environment with no ongoing input of those healthy sources of microbes from the outside,” said co-author Robin Knight, a computational microbiologist and professor at UCSD and leader of the Knight Lab.

Looking to the future, the researchers hope to refine their analyses to detect potentially pathogenic microbes and how environmental metabolites could be used as indicators for astronaut health. The team claims that these methods could also help improve the health of people living and working in similarly sterile environments on Earth.

This research was supported by the National Institute of Health (NIH), the Alfred P. Sloan Foundation, UCSD, the Center for the Advancement of Science in Space (CASIS), and the ISS National Laboratory. The paper detailing their findings, “The International Space Station has a unique and extreme microbial and chemical environment driven by use patterns,” was published on February 27th in the journal Cell.

Further Reading: EurekAlert!

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