Microbes in space

Note from Justine: This guest post by Camila Castillo-Vilcahuaman provides a journey to space with bacteria.

As a child, I was fascinated with space, which probably was pretty common for other children around my age. I learned all of the planets and stars. There was also this big research place-thing in our planet’s orbit, called the International Space Station. From the photos in my little space encyclopedia, I saw astronauts floating around in that place (that zero-gravity stuff). 

After some biology classes, a little bit of day-dreaming and some thinking, I asked myself this question in my first year of my undergrad: if we humans are surrounded by skin microbiota, does that mean that those astronauts were surrounded by their microbiota too? Which means, are there any bacteria in the International Space Station?

So, let’s explore the concept of microbes traveling to space and living in the International Space Station (ISS). In this post, I’ll cover how microbes ended up in the ISS, how space agencies treat microbial stowaways, what microbes are in the ISS, and how they adapted to living there.

The International Space Station

The ISS is a habitable artificial satellite located in low Earth orbit. It was launched in 1998 and serves as a space research laboratory. Crew members can perform experiments in different fields, such as biomedical research, biotechnology, and fluid physics.

As the ISS orbits the Earth, astronauts still experience 90 percent of the gravity they would on the Earth’s surface. However, they can float, which might be perceived as being weightless. This is called microgravity. The truth is, all objects and crew members inside the ISS are in free fall. And since they are falling together, it appears as if they are all floating. Microgravity will be a key component in this story.

And where there are people, there will be microbes.

How space agencies treat microbial stowaways

So, how do space agencies deal with microbial astronauts? 

When a NASA mission leaves Earth, they have to meet internationally accepted standards for Planetary Protection (yes, just like in the Marvel movies). These standards are important because we want to cause minimal impact on the places we visit in space. We have enough issues with contamination on our own planet. But here, we’re dealing with the danger of having unknown creatures sneaking out. For missions to other planets, for example, the protocols must be rigorous. But for spacecraft that will not be in contact with other environments, things can be a little bit more relaxed. Probably the cleanest places on Earth are the assembly facilities at NASA. And although they heat microbes to 80 degrees Celsius for 15 minutes, some sneaky bugs still remain. In fact, this is how we discovered the new bacterial species Tersicoccus phoenicis—because those bugs resisted these sterilization protocols.

The European Space Agency (ESA) will also apply these planetary protection protocols with their project ExoMars. And for them, it is crucial to be extremely careful because ExoMars is actually intended to search for new life on Mars. Can you imagine what would happen if this rover landed on Mars without any sterilization whatsoever? Earth microbes everywhere.

ISS… yuck! 

Despite all my childhood dreams, it seems that the ISS is not as pleasant as I thought. Turns out that it smells. And it’s pretty bad. 

We can all guess what is going on inside there. Yes. Microbes. And they seem to be as happy as they can be.

Researchers have actually looked at what microbes are in the ISS by sampling the surfaces around the space station. It isn’t surprising that the most abundant bacteria are commonly associated with humans, such as those from the orders Actynomycetales and Bacillales (common on human skin and oral cavity) and Lactobacillales (specifically Streptococcus species, common in the human oral cavity). It also seems that the ISS is a diverse environment, rich in different bacterial groups, similar to those found on house surfaces.

Isn’t it amazing that microbes can live in these conditions? But if no disinfection can harm these microbes, and they manage to make it out to space (kudos to them) then how are they adapting to their new place?

Zero-gravity adaptations

One of the key concepts to understand about bacteria is just how efficient they are. Bacterial genomes do not waste their time with unused genes. And if a problem arises, they are capable of finding a new solution through mutations.

To discover new adaptations, researchers have to do experiments. But if they want to figure out which mutations are responsible for the adaptations to life on the ISS, it is much simpler to do controlled experiments with a model organism.

First of all, how do bacteria handle microgravity, which is what we might think of as the biggest obstacle on the ISS? To figure this out, scientists exposed an Escherichia coli strain to microgravity and compared that to E. coli under normal circumstances (with gravity). After the thousandth generation, the microgravity strain had outgrown the normal-gravity one. More interestingly, after the microgravity strain was returned to normal gravity, its descendants still retained 72% of the newly acquired advantages. Yes, this means that this strain could pass on its new “superpowers.” Some of these genes are involved in biofilm formation.

This is where we might stop for a brief explanation of biofilms. Biofilms are all of our horror stories-based dreams of a living and breathing mucus. The only difference is that, well, it is composed of bacteria. Biofilms are a structure that bacteria form as a way to adapt to certain environments. Our oral cavity is full of bacteria living as biofilms in the form of plaque on our teeth, for example. In fact, most bacteria on Earth probably take this form instead of a planktonic, “free” form. This “biofilm-mode” allows them to resist certain environmental stresses.

A modelled microgravity experiment showed, for example, that, under microgravity, E. coli formed thicker biofilms and was more resistant to stressors, such as salt, ethanol, and antibiotics. Other microgravity experiments with the bacterium Pseudomonas aeruginosa showed thicker biofilms compared to those biofilms made on Earth.

Microgravity also affects the virulence of certain microorganisms, such as Salmonella typhimurium, Listeria monocytogenes, and Enterococcus faecalis. Some of these bacteria have actually become more resistant to antibiotics in this environment, which may put some selective pressure on the station’s microbiota. 

Of course, nothing is as exciting as observing the real thing. Microgravity experiments may provide insight into bacterial adaptations, but what about bacteria that actually went there? Experiments with cultures of Pseudomonas aeruginosa on the Space Shuttle Atlantis give us some insights into bacterial adaptations: spaceflight increases the number of viable cells and biofilm mass and thickness. More interesting, however, is the fact that the biofilms produced in this spaceflight had a novel architecture, never seen on Earth. Other bacteria that went to the ISS, such as Bacillus subtilis, had increased expression of their biofilm formation genes.

Amazing stowaways

In a way, the first alien being will probably be one that we ourselves have created with our mighty technology. We may discover a new species of bacteria on the ISS, a product of all those generations of being exposed to harsh conditions such as microgravity. Although the future of the ISS is uncertain, the ability of microbes to survive in space is clear. This has been a wild ride, and I hope you enjoyed discovering these microbial stowaways.

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Camila Castillo-Vilcahuaman is a biologist from Peru. She plans to start her Masters in Molecular Biology and Biochemistry soon. Right now, she collaborates at the Microbial Genomics Laboratory at Universidad Peruana Cayetano Heredia. Her research usually revolves around genomics, metagenomics, bioinformatics, and microbial ecology. She’s also a member of the Sociedad Científica de Astrobiología del Perú (Scientific Society for Astrobiology in Peru) and has participated in martian simulations at the Mars Desert Research Station (MDRS) in Utah – USA. You can find her on Twitter or visit her website.