How microbes from Earth can help astronauts adapt to long-term space missions

Astronauts living in isolated, sanitized space habitats for long periods of time could stay healthier by being exposed to a greater variety of microbes from Earth, according to a new study.

"Sterile environments are not in fact the safest environments," study co-author Rob Knight, a professor at the University of California, San Diego, told Space.com. "Exposure to beneficial microbes in the environment is important for maintaining health — this is not surprising because, as humans, we have coevolved with those environmental microbes for millions of years."

Astronauts aboard the International Space Station (ISS) face unique stressors that impact their bodily functions. These include exposure to microgravity and radiation that affect their immune responses; a human body with a healthy immune system needs to work harder in space to overcome the same infection that'd be relatively easier to fight off on Earth, according to NASA research.

Previous studies have attributed persistent medical conditions astronauts on the ISS have reported, such as skin rashes, cold sores and some atypical allergies, to their altered immune systems. With this in mind, a new study produced by Knight and his colleagues suggests that it's possible to boost astronauts' immune systems and overall health — without compromising their hygiene — by intentionally introducing diverse communities of microbes from soil and water that have coexisted with humans for millennia.

The team's findings are based on an analysis of 803 surface samples swabbed across the U.S. portion of the ISS, resulting in the largest dataset illustrating the habitat's microbial and chemical landscape. The results showed the presence of microbial communities were largely specific to their environments; for example, microbes from food were prevalent in dining and food storage areas, while fecal-associated microbes were more abundant in the Waste and Hygiene Compartment, aka the space toilet.

Comparing those samples to thousands of samples collected here on Earth showed the ubiquity of chemicals throughout the ISS that come from cleaning products and disinfectants, similar to industrialized, isolated spaces on our planet like hospitals and urban homes. Overall, the survey reflects a loss of microbial diversity on the highly-sanitized ISS, which is a notable concern and marks the station suboptimal in supporting the astronauts’ immune functions.

"We hope the impact of this research will be to guide future studies that keep astronauts healthy during extended space travel and in colonizing space," Knight said.

Before introducing new microbes to the ISS environment — such as those from Earth’s soil and water — scientists must assess whether microbes that are typically harmless to human health could become harmful in space. This potential risk may arise from reduced microbial diversity or increased mutation rates triggered by radiation, Knight noted: "These factors can be tested on Earth before proceeding to costly space experiments."

The study was published on Wednesday (Feb. 27) in the journal Cell.