The Diverse Microbiome of the ISS

The International Space Station (ISS) is one of the largest platforms where astronauts reside and perform a number of tasks and space-based research projects.

Since its establishment, a variety of microorganisms have travelled up to space along with the cargo and the crew. This has ultimately caused the International Space Station to have its very own unique microbiome.

Microbiome refers to the complete collection of all different kinds of microorganisms that inhabit a particular environment. We are very well aware of how diverse the human microbiome is.

Ticketless Passengers

Imagine the number of microorganisms that gain entry into the International Space Station every time a fresh crew of astronauts visit it!

The ISS is always inhabited with astronauts. Almost every six months, a fresh crew of astronauts travel to the space station.

Even though the astronauts are quarantined before the flight to ensure that they are healthy and are not carrying any infectious diseases onto the ISS, it is almost impossible for them to travel alone.

This is because they are always accompanied by their gut microbiome and other friendly bacteria that help in keeping the astronauts healthy.


Image-1. Air, water, and surface samples on the International Space Station (ISS) are regularly collected by the crew members to monitor the changes in the ISS microbiome. (Image Credit: NASA)

Over all these years, several astronauts have been carrying out their daily routine activities at the ISS.

This must have led different kinds of microorganisms to be released into the environment. As the ISS is a closed system, these microbes get stuck around and slowly increase in numbers.

Which Microorganisms?

Samples collected from the interior of the space station have shown the presence of microorganisms like Staphylococcus aureus, Staphylococcus epidermis, Micrococcus luteus, Burkholderia and Sphingomonas to name a few. Apart from this, certain technophilic microorganisms (ones that pose a risk to material integrity of a spacecraft) have also been found.

One such incident that involved technophilic microorganisms was seen on the former Russian space station MIR where organisms like Bacillus, Aspergillus, and Penicillium caused extreme damage of a window in MIRs descent module, and a mold growing on the wiring connectors caused electrical problems.


Image-2. Dust mite found floating in a globule of water onboard the Russian spacecraft MIR. (Image Credit: NASA)

The ISS microbiome is in continuous interaction with the microbiome of each of the crew members. Studies have shown that microgravity leads to a decrease in the immunity of the astronauts.

Alterations in the ISS microbiome can thus have detrimental effects on the health and well-being of the crew. It is important that we study and analyze the growth patterns of these microorganisms as microgravity has an effect on almost everything, and that includes these organisms too.

Increase in the virulence of some microbes like Salmonella typhimurium, Enterococcus faecalis, and Listeria monocytogenes have been observed on the ISS. Additionally, the harsh conditions in space can also cause the organisms to increase their resistance to antimicrobials.

Organisms like Corynebacterium, Klebsiella, Cryptococcus, Rhodotorula, etc. that are well known for their biofilm-forming activity have also been found onboard the space station.

Biofilms formed by these organisms are dangerous as they can cause infections in astronauts due to their ability to develop antibiotic resistance, and can also pose problems to the infrastructure of the ISS by inducing microbial-induced corrosion.


Image-3. Fungi found on the International Space Station growing on a panel of the Russian Zarya Module where exercise clothes were hung to dry. (Image Credit: NASA)

In a study carried out to characterize the different microorganisms present on the ISS, surface-wipe samples from eight locations within the ISS were brought back to Earth. Analysis was carried out using culture-based techniques, quantitative PCR, and amplicon sequencing of the 16S rRNA gene and the internal transcribed spacer (ITS) region.

It was seen that the bacterial and fungal population on the ISS environmental surfaces changed over time, but still remained similar across locations.

Additionally, many of these organisms were the ones that are normally associated with humans, while some of these were opportunistic pathogens. Even though the astronauts were not affected by these pathogens, the harsh conditions in space can cause certain alterations in the genome of these organisms which could ultimately make them have a negative impact on the astronauts’ health.

Today, it is possible to study the diverse microbiome of the International Space Station in real time using specific gene sequencing technologies.

This is extremely helpful as it allows the crew to find out any changes taking place in the ISS microbiome which in turn helps them in monitoring the health of the crew.


Image-4.  Microbial culture slide from a particular location onboard the International Space Station. (Image Credit: NASA)

As we continue to explore the space, and aim to build human habitats on Moon and Mars, it is important that we have a deep knowledge of how different microorganisms act in closed environments like that of the International Space Station.

Moon- and Mars- Based Laboratories

Moon- and Mars- based laboratories should definitely have the technology that would enable them to keep their internal environment in check. This would help in ensuring that our astronauts do not get sick during the mission, and also do not contaminate other extraterrestrial locations unknowingly.


  • Mora, M., Wink, L., Kögler, I. et al. Space Station conditions are selective but do not alter microbial characteristics relevant to human health. Nat Commun 10, 3990 (2019) (URL).
  • Checinska Sielaff, A., Urbaniak, C., Mohan, G.B.M. et al. Characterization of the total and viable bacterial and fungal communities associated with the International Space Station surfaces. Microbiome 7, 50 (2019) (URL).
  • National Public Radio- ‘A Microbe Hunter Plies Her Trade in Space’ (URL)
  • ISS National Laboratory- ‘These Tiny Organisms are a Big Deal’ (URL)

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Nitya Shailesh Palekar

Mars on Earth Project-MoEP (India) Volunteer and Author. M.Sc. Biotechnology - Ramnarain Ruia Autonomous College

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