Bugs in space: the battle to keep the ISS clean

We share our lives with microbes, from the mites chowing down on our dead skin to the bacteria in our gut helping us digest food. Many are essential to how we function here on Earth – but did you know that the International Space Station (ISS) is brimming with them too?

Turns out that if you take a partially closed built environment and fill it with humans for a couple decades, you’ll end up with a pretty interesting microbial community.

This shouldn’t be a surprise. In 1998, astronauts aboard the Russian space station Mir were curious to know about the microbes they were sharing their living space with. When they opened an inspection panel, they found large globules of murky water teeming with bacteria, fungi and mites. Even more concerningly, they discovered organisms eating away at the rubberised seals around the windows, and bugs that excrete acid working their way through the electrical cabling.

The ISS was launched that same in year, in 1998, and at the time it was absolutely pristine.

It has since been zooming around in low Earth orbit (at an altitude of 400 kilometres above the surface) for more than 22 years. It’s been continuously occupied over that time by a stream of nearly 250 astronauts, and all those humans have brought with them a complex assortment of microbes.

So what kinds of critters make it to space?


Scientists have identified more than 55 species of bacteria on the ISS, which were published in 2019 in a comprehensive catalogue.

In that study, samples were collected from eight locations across the space station, including the viewing window, toilet, exercise platform, dining table and sleeping quarters.

Purple balls
Staphylococcus. Credit: Wikimedia Commons.

The types of microorganisms found were similar to those found on Earth, and the most abundant bacteria were Staphylococcus, Pantoea and Bacillus. This suggests that the ISS’s microbial community is shaped by human occupation, which was backed up in a later study that found that these communities change as astronauts rotate through.

Fungi, moulds, protozoa and viruses have also been found.

Interestingly, despite the lack of gravity, many of these species have adapted well to their surroundings. With only a small amount of gravity, many normal processes (like convection and buoyancy) are minimised, while others (like liquid surface tension and capillary forces) become more intense. While it’s still not entirely clear how these changes affect microbes, studies suggest that bacteria mutate quicker in space to adapt.

Are these bugs different to the bugs down here?

Earlier this year, a study identified four new species of bacteria, all belonging to the Methylobacteriaceae family. Three of these were previously unknown to science, prompting the question – are space bugs different to those on Earth?

According to the researchers: no. It’s common to discover new types of bacteria, and in fact there might be hundreds of currently unknown species on the ISS (and in every spoonful of soil on Earth, too).

Read more: It’s safer inside the ISS than out

But the space station’s microbial community may have a different make-up than ground-based ones.

In 2015, a NASA-led study published in the journal Microbiome found that most of the bugs on the ISS are associated with human skin, specifically Corynebacterium and Propionibacterium (Actinobacteria) species.

This was different when comparing to “clean rooms” on Earth, which are used to simulate the ISS environment. These clean rooms are dominated by Proteobacteria species – which were the least abundant on the ISS. Hugely diverse, Proteobacteria are the most abundant type in the human gut microbiota, and include many pathogens like those responsible for gastrointestinal diseases.

Can these bacteria harm human health?

Space bugs seem problematic for astronauts, given that their immunity might be weakened by periods of stress, and that they don’t have access to the same medical resources as on Earth.

But a 2020 study led by the European Space Agency (ESA) found that microbes on the ISS aren’t more resistant to antibiotics than those on Earth, and nor are they more extremophilic (able to thrive in inhospitable environments).

That doesn’t mean they aren’t potentially harmful, but at least they aren’t superbugs.

The same study also found that the microbes were adapting to the ISS itself.

“We found indications that the microbes are adapting to the surfaces on board,” explains lead researcher Christine Moissl-Eichinger, of Medical University of Graz in Austria. “These microbes were really different to those that we found on the ground. These technophilic organisms are attacking the surfaces as they struggle to stay alive.”

This is similar to the “technophilic” critters found aboard Mir, which attacked metal areas, window seals and wiring connectors.


Perhaps most concerningly is how spaceflight has been found to promote the formation of bacterial ‘biofilms’ – when colonies of cells pack together and produce substances that allow bacteria to stick to each other and to surfaces, creating a film. A 2013 study found that biofilms make bacteria more resistant to antibiotics and improve their ability to cause infection.

These biofilms have been seen to grow on the ISS. But this ageing space station definitely doesn’t need the extra stress of microbes attacking its infrastructure.

Read more: ISS struck by space junk

Though the station has well out-lasted its initial lifespan of 15 years, it’s slowly falling apart from use. Cracks have recently been found on the Zarya module; a software glitch earlier in the year sent the station momentarily off-course; a Russian toilet went bust; an oxygen-supply system broke down; and a notorious air leak is slowly growing larger.

The last thing astronauts need is a microbe problem.

But can’t they just… clean?

How do astronauts clean the space station?

For astronauts, Saturday is not a day of rest – they’re up early, sticking to their strict cleaning schedule.

“We have to disinfect all the surfaces we touch every week,” ESA astronaut Thomas Pesquet said in a call with journalists earlier in the year. “We also have a lot of measures on the space station that are similar to those you can find in hospitals or at airports that are designed to prevent the propagation of bacteria.”

This includes using disinfectant wipes to sanitise handrails, microphones, computers and anything else regularly touched; changing the air purification system’s filters; and even vacuuming to pick up dust – very important, since dust doesn’t settle in the space station, it just floats around.


(In case you’re wondering: yes, you can ride a vacuum cleaner in microgravity. Russian cosmonaut Anton Shkaplerov tried it out.)

Anyway: astronauts also rely on technology to filter the air and keep the water clean. The space station is a partially closed system, equipped with interconnected, interdependent life support machines that provide breathable air and pure drinking water.

Experience from Mir is useful, too, showing that microbes usually thrived in wet areas, so it’s key to keep surfaces dry.

Read more: Ten things to take on your next trip to space

Plus, scientists are working to prevent microbes from sticking to surfaces in the first place. Three separate experiments in the past few years have tested antimicrobial surface coatings on the ISS, designed to repel bacteria.

One promising coating, made of silver and ruthenium, was tested on one of the most disgusting surfaces in the space station — the toilet door. It worked pretty well, with 80% fewer bacterial strains after 12 months than the control (an uncoated area of steel).

“Most importantly, no serious human pathogens such as methicillin-resistant Staphylococcus aureus or vancomycin-resistant Enterococci were found on any surface,” the researchers noted in the 2019 paper in Frontiers in Microbiology. “Thus, the infection risk for the crew is low.”


Studies like these will be key to informing future long-haul missions to the Moon, Mars and beyond, because we take our microbiome with us everywhere we go.

As soon as you leave low Earth orbit and jet out into the Solar System, it gets a little harder to perform routine maintenance – you don’t get a regular resupply of cleaning products, for one.

So scientists are using the ISS while they can to better understand microorganisms, how they evolve in the conditions of space, and how they affect the crew and infrastructure.

Two decades (23 years come November) is a long time to go without a deep clean, but for the sake of science, maybe it’s for the best.

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