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Excessive cleanliness is not generally regarded as a downside when it comes to travel accommodation. However, scientists have concluded that the International Space Station is so sterile that it could be having a negative impact on astronauts’ health and have suggested making it “dirtier”.
The study found that the ISS is largely devoid of environmental microbes found in soil and water that are thought to beneficial to the immune system. The lack of microbial diversity could help to explain why astronauts often experience immune-related health problems such as rashes, cold sores, fungal infections and shingles.
In future, putting these microbes in space stations could improve astronaut health without sacrificing hygiene, the researchers advised.
“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 sanitised spaces,” said Rodolfo Salido of the University of California, San Diego and a co-author of the paper.
The researchers collaborated with astronauts who swabbed 803 different surfaces on the ISS. Back on Earth, they identified which bacterial species and chemicals were present in each sample.
Overall, human skin was the main source of microbes throughout the ISS, although the prevalence varied across different areas of the station. The dining and food preparation areas contained more food-associated microbes, whereas the space toilet contained more species associated with urine and faeces. Compared with most of the Earth samples, the ISS surfaces were lacking in free-living environmental microbes that are usually found in soil and water.
Prof Rob Knight, a microbiologist at the University of California, San Diego and a senior author on the paper, said: “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.”
Chemicals from cleaning products and disinfectants were present ubiquitously throughout the station. The ISS was most similar to Earth samples from industrialised, isolated environments, such as hospitals, according to the paper, which has been published in the journal Cell.
“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,” said Salido. “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.”
Dr Odette Laneuville, a biologist at the University of Ottawa who was not involved in the research, said: “The environment is important for the immune system because it senses constantly those pathogens and it triggers a response or not.”
However, she said caution would be required when considering intentionally seeding a space environment with microbes from Earth. “I don’t want parasites and fungi up there,” she added.
