NEW YORK – A University of California, San Diego-led team has documented the microbial communities and chemical compounds found at sites in the International Space Station (ISS), highlighting microbes and metabolites that matched up with human activities performed in different parts of the space station, within a broader context of reduced microbial diversity and industrialization-related features.
"It is important to monitor space crews' exposures, as they can impact health," Pieter Dorrestein, director of UCSD's Collaborative Mass Spectrometry Innovation Center and codirector of the Institute for Metabolomics Medicine, said in an email. "Space travel has been linked to increased antimicrobial resistance, reactivation of latent viruses, and alterations in the immune system."
For a paper appearing in Cell on Thursday, Dorrestein along with co-senior author and UCSD researcher Rob Knight and colleagues used targeted 16S ribosomal RNA sequencing, shotgun metagenomic sequencing, and mass spectrometry to evaluate microbial community members, microbial gene content, and metabolomic/chemical features found in 803 pairs of dry surface swab samples collected from environmental surfaces in an ISS "United States Orbital Segment" (USOS) operated by the US.
In the process, the team generated more than 31 million 16S sequences, some 3.7 million metagenomic reads, and almost 21,000 chemical features from the surface samples.
The resulting, publicly accessible dataset "allows us to identify key factors that need attention for long-term space travel and even the potential habitation of other planets," Dorrestein said, adding that "we should also consider the absence of certain chemicals and how their depletion may contribute to changes in health outcomes."
Overall, the team's 3D "microbial mapping" survey of the ISS pointed to a dramatic drop in microbiome diversity in the space station samples considered relative to natural or built environments on Earth, hinting at the absence of potentially beneficial bugs and microbiome features.
Microbial communities that did turn up in the ISS samples broadly coincided with activities performed at each sampling site — from an uptick in food-associated microbes in a dining module to fecal microbes in a toilet module. Human skin microbes also turned up at sites sampled across the space station.
"[B]y comparing these findings to microbial compositions in Earth human habitats, we established that the space station is much more similar to hospitals and isolation dorms used during the pandemic than to typical homes and completely dissimilar to homes in remote villages," Dorrestein said.
Similarly, when the investigators used tandem mass spectrometry to track chemical components found at different space station sites, they saw what he called "usage-driven patterns that complemented the microbial sequencing data." These included chemicals associated with cleaning products and over-the-counter allergy medication, for example, as well as pepper- and citrus-derived molecules in the kitchen and toilet module molecules traced back to metabolites found in urine or feces.
More broadly, the team identified metabolite patterns that resembled those in particularly industrialized environments on Earth, along with the presence of "perfluoroalkyl and polyfluoroalkyl substances" (PFAS) chemicals nicknamed "forever chemicals."
But still other chemicals did not coincide with those reported in other environments in the past.
"What stands out most in this dataset is how few of the molecules we could annotate and trace to their sources," Dorrestein noted, adding that this means that astronauts are exposed to chemicals that are unknown or have unknown effects.
Members of the team plan to continue analyzing these molecules in relation to those identified on Earth so far, with an eye to understanding the health effects they may have on humans venturing into space.
"For space travel, the longstanding goal has been to maintain a highly sterile environment to prevent contamination of other planets," Dorrestein explained. "However, this approach may have unintended health consequences for space travelers."
"Striking a balance will be crucial," he added, "ensuring the right exposures to support human health while minimizing contamination of outer space."