Astronauts frequently suffer from immune dysfunctions, skin rashes, and other inflammatory issues when traveling in space. A study published in the Cell Press journal suggests that these problems may be due to the overly clean nature of spacecraft.
The study showed that the International Space Station (ISS) has a far lower microbial diversity compared with human-built environments on Earth, and the microbes present are mainly human-carried species to the ISS, suggesting that the presence of more microbes from nature could help improve human health on the space station.
“Future built environments, including space stations, may benefit from the intentional promotion of diverse microbial communities that better mimic the natural microbial exposures experienced on Earth, rather than relying on highly sanitized spaces,” says co-author Rodolfo Salido of the University of California, San Diego (UC San Diego).
The researchers collaborated with astronauts who collected 803 samples from different surfaces on the ISS — about 100 times more samples than were collected in previous studies. Back on Earth, they identified the bacterial species and the chemicals present in each sample. They then created three-dimensional maps illustrating where each of them was found on the ISS and how the bacteria and the chemicals may be interacting.
The team found that, overall, human skin was the main source of microbes throughout the ISS. The chemicals from cleaning products and disinfectants were present ubiquitously across the station.
They also found that different “modules” or rooms within the ISS housed different microbial communities and chemical signatures, and that these differences were determined by the module’s use. For example, the dining and food-preparation areas contained more food-associated microbes, while the space bathroom housed more microbes and metabolites associated with urine and feces.
“We noted that the abundance of disinfectant on the surface of the International Space Station is highly correlated with the diversity of the microbiome across different locations on the space station,” says co-author Nina Zhao (@NinaHaoqiZhao) of UC San Diego.
When they compared the ISS with different human-built environments on Earth, the researchers found that the ISS microbial communities were less diverse than most Earth samples and were more similar to samples from industrialized and isolated environments, such as hospitals and closed habitats, and homes in urbanized areas.
Compared with most Earth samples, the ISS surfaces lacked free-living environmental microbes typically found in soil and water. The intentional incorporation of these microbes and the substrates in which they live on the ISS could improve astronauts’ health without sacrificing hygiene, the researchers say. The researchers compare their suggestion to the beneficial impacts of gardening on the immune system, which have already been well studied.
“There is a big difference between exposure to healthy soil from gardening and exposure to our own filth, which is more or less what happens if we are in a strictly closed environment, with no ongoing input of those healthy external microbes,” says Knight.
In the future, the researchers hope to refine their analyses to detect potentially pathogenic microbes and signals of human health from environmental metabolites. The researchers say that these methods could also help improve the health of people who live and work in equally sterile environments on Earth.
“If we really want life to thrive beyond Earth, we can’t simply take a small branch of the tree of life, fling it into space and hope it works,” says Salido. “We need to start thinking about what other beneficial companions we should send with these astronauts to help them develop ecosystems that are sustainable and beneficial for everyone,” he concludes.
