Unwelcome space travelers have swarmed the International Space Station (ISS). Some are recognized on Earth as notorious germs. However, extreme living conditions in space could affect their ability to infect astronauts.
The International Space Station (ISS) houses in its bowels a microbiota composed of countless bacteria and fungi that a study of NASA has identified for the first time by duplicate analysis combining culture and microbial sequencing of DNA. The majority of bacteria are staphylococci, including the formidable Staphylococcus aureus (Staphylococcus aureus), and Enterobacteriaceae, which are commonly found on and inside the human body, respectively in the respiratory tract and on the skin for the first, and in the intestines for the latter. Rhodotorula mucilaginosa, a pathogenic species, dominates mushrooms.
The ISS micro-organism community closely resembles the community living in enclosed human-occupied environments on Earth, such as sports halls, office buildings and hospitals. They were more abundant in places most visited by astronauts, such as rest areas, the dining table or the toilet, according to the study, led by researchers at the Jet Propulsion Laboratory (JPL), and published in the journal Microbiome.
Potential infectious and corrosive agents
Between March 2015 and May 2016, the microorganisms have been taken three times by astronauts of NASA, Terry Virts and Jeffrey Williams, on various surfaces in eight locations across the US segment of the ISS. This included the observation dome, the toilet, the weight machine, the dining table, the astronaut quarters, and storage space. The samples were sent back to Earth for study.
The analysis of microbial cultures indicates that the majority of bacteria are staphylococci (26%), Pantoea bacteria (23%) and bacilli (11%). Recognized pathogenic bacteria are particularly well represented, such as Staphylococcus aureus (11%) and Pantoea conspicua (9%). In the results of the other method of analysis, based on DNA amplification and sequencing, enterobacteria predominate (more than 50%), followed by bacteria of the genus Methylobacterium (13%) and staphylococci (10%).
Among the cultivated mushrooms, the two most abundant species are Rhodotorula mucilaginos (41%), responsible for infections in humans, and the famous Penicillium chrysogenum (15%) at the origin of the discovery of penicillin. According to the researchers, the risks of pathogenic bacteria and fungi infecting ISS astronauts “depend on the health status of each individual and the way organisms function in the space environment.”
In addition to the potentially infectious agents, bacteria and fungi identified on the ISS in this study could degrade the materials, by microbial corrosion by forming biofilms. Researchers point to bacteria of the genus Methylobacterium, genus Sphingomonas and bacilli (Bacillus), as well as fungi of the genus Penicillium and Aspergillus.
An extreme environment under human influence
By carrying out their study on eight different sites over 14 months, corresponding to three missions, the researchers were able to gain insight into the spatial and temporal evolution of the microbiota of the ISS. No significant changes were detected for fungi. On the other hand, the diversity of the bacteria was richer during the second mission on all the surfaces sampled, probably because the crew of the astronauts changed during the study.
Microorganisms land on the ISS over time, carried by astronauts or hidden in cargoes. Microgravity, lack of ventilation and cosmic radiation are all factors that can lead to resistance and virulence. Without sounding the alarm, this study underscores the need to assess the threat that microbes pose to the health and safety of astronauts in order to put in place adequate protective measures. This is not only true for missions aboard the ISS, for future journeys to the Moon or interplanetary, but also for other sensitive enclosed spaces on Earth, such as hospital environments, the researchers specify.
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