During the last twenty years, the International Space Station (ISS) has seen hundreds of astronauts come and go. However, even after all these years, a small part of each visitor remains, like a signature in the station's guestbook.
The most extensive microbial inventory to date has found an astonishing diversity of germs on board the ISS, and most are from humans, and possibly date back to the first visitors.
A true heterogeneous mixture of bacteria and fungi, this constantly growing and constantly changing community has the microbial footprint of a gym, hospital or office. Like any other community space in which humans find themselves, it could also pose a threat to our health.
Microbes are everywhere here on Earth, and not all are bad, but some of the ones discovered on board the ISS, including Staphylococcus Y Enterobacter, are known to be opportunistic, sometimes causing infections in humans.
"It is unknown whether these opportunistic bacteria could cause diseases in the ISS astronauts," says one of the study's authors, Aleksandra Checinska Sielaff, a microbiologist at Washington State University.
"This would depend on several factors, including the health status of each individual and how these organisms function in the space environment."
It is known that microbes survive in extreme environments, and space is quite challenging. Even within the sealed system of the ISS, these germs are subjected to microgravity, radiation, high carbon dioxide and the recirculation of air through HEPA filters.
As humans aspire to venture further into space, it is important that we understand what happens to our germs.
"This is even more important for astronauts during space flight, as they have altered immunity and have no access to the sophisticated medical interventions available on Earth," says co-author Kasthuri Venkateswaran, microbiologist at the Jet Propulsion Laboratory of the POT.
Sampling surfaces at eight locations along the ISS, including the viewing window, the toilet, the exercise platform, the dining table and the bedrooms, the extensive study measured the station's microbial community over time of 14 months.
What they found was a thriving community of microbes, but while fungal groups remained relatively stable over time, the bacterial groups seemed to fluctuate along with the ever-changing crew.
At 26 percent, the most prominent bacteria was Staphylococcus, followed by Enterobacter to 23 percent and Bacillus to 11 percent. Meanwhile, the most abundant mushrooms were easily Rhodotorula, occupying 40 percent of the entire community.
The four microbes are badociated with infections here on Earth.
But it's not just astronauts' health that worries the authors. They argue that the integrity of the ISS itself should also be investigated, since some of the microbes they found are badociated with corrosion.
"In addition to understanding the possible impact of microbial and fungal organisms on the health of astronauts," says Camilla Urbaniak, microbiologist at NASA's JPL, "understanding their possible impact on spacecraft will be important to maintain the vehicle's structural stability. of the crew during a long-term space, missions when routine interior maintenance can not be done so easily. "
Of particular concern is the fact that many of the microbes detected in the ISS are known to form biofilms, a thin, viscous layer that adheres to surfaces.
The authors explain that this could cause problems for astronauts if they become infected, because it is known that biofilms promote resistance to bacteria.
"In addition, the formation of biofilms in the ISS could decrease the stability of the infrastructure by causing mechanical blockages, reduce the efficiency of heat transfer and induce corrosion influenced by microbes," the authors added.
This study has been published in. Microbiome.