A trip to space is not always as pleasant an experience as portrayed by Jesús Calleja. Not even as described by most astronauts who have ventured beyond the Kármán line. Behind the exclusive view of our planet from outer space, there is fine print upon return to Earth, which includes immune dysfunction, skin rashes, and other inflammatory conditions.
A study just published in the journal Cell Press suggests that all these issues are due to the excessive sterilization of spacecraft. The study showed that the International Space Station (ISS) has fewer microbes than human-built environments on Earth. In fact, the few present are species brought by humans to the ISS and by the humans themselves, suggesting that a greater presence of microbes could help improve astronauts' health on the space station.
"Space stations could benefit from intentionally fostering diverse microbial communities instead of building highly disinfected spaces," notes study co-author Rodolfo Salido from the University of California, San Diego (UC San Diego).
Researchers collaborated with astronauts who took samples from 803 different surfaces on the ISS and identified which bacterial species and chemicals were present in each sample. They then created three-dimensional maps illustrating the location of each on the ISS.
The team found that human skin was the main source of microbes. At the same time, cleaning products and disinfectants were present throughout the station. They also discovered that different modules or rooms within the ISS harbored different microbial communities. For example, food preparation and dining areas contained more food-associated microbes, while the space toilet contained more microbes and metabolites associated with urine and feces.
"We noticed that the abundance of disinfectant on the surface of the International Space Station is highly correlated with the microbiome diversity in different locations of the space station," says co-lead author Nina Zhao from UC San Diego.
When comparing the ISS to different human-built environments on Earth, researchers found that the microbial communities of the ISS were less diverse than most Earth samples and were more similar to samples from industrialized and isolated environments, such as hospitals.
Compared to most Earth samples, ISS surfaces lacked free-living environmental microbes typically found in soil and water. Therefore, intentionally incorporating these microbes and the substrates they live on in the ISS could improve astronauts' health without sacrificing hygiene. Researchers liken their suggestion to the beneficial effects of gardening on the immune system.
"There's a big difference between exposure to healthy soil through gardening and living in our own filth, which is what happens if we're in a strictly closed environment without the constant influx of those healthy microbial sources from the outside," says Knight.
In the future, researchers hope to refine their analyses to detect potentially pathogenic microbes and human health signals from environmental metabolites. They say these methods could also help improve the health of people living and working in similarly sterile environments on Earth.