#Conclusion

This is the first time that the ISS has been analyzed in the broader context of the "microbiology of the built environment", and is the most in-depth comparison of the microbial communities found on the ISS to those found either in buildings or in the human microbiome. Perhaps surprisingly, given the extreme rarity of exchange with any external microbes, we found the ISS to be species-rich, and more similar to the surfaces of human homes on Earth than it is to human bodies. We found that the ISS is home to at least 12,554 distinct microbial species, including Archea in very low abundance, and that the proportion of species that are closely related to known human pathogens is on par with similar built environments on Earth.

As outlined in the 2010 U.S. National Space Policy and in the bipartisan NASA Authorization Act of 2010, NASA is targeting the 2030s for a manned spaceflight to Mars, with one ultimate goal of having people live and work on the Martian surface (see www.nasa.gov/exploration and www.nasa.gov/mars). We know that the microbial communities found in our terrestrial built environments play an important role in human health. Therefore it’s crucial to characterize and understand the microbial population of the only environment in which people are currently living and working in space. This study is one small step in that direction.