Today the International Space Station (ISS) is the main crewed, long-term habitable spacecraft. Over 200 astronauts have lived on the ISS, even if just has been for some days! Living in space is nothing like living on Earth. Gravity is missing, radiation levels are higher and one could argue about the comfortable interior design.

Being an indoor-closed habitat with controlled moisture and temperature makes it good for humans, but it also makes it good for microorganisms. As research missions increased in both number and duration, scientists were interested in knowing what kind of microorganisms would be there, and so began to screen for microbial contamination aboard the ISS. Astronauts took samples of the walls, windows, air filtration systems, water and urine systems, and food (such as lettuce) that was grown onboard the spacecraft. Culturing and DNA sequencing techniques helped identify the “space microbes” living on the ISS. Among many many microbes, there were two: Penicillium and Aspergillus. Are they mushrooms? No. Yeasts? Nope. Oh, I know! They’re filamentous fungi! (Also known as molds).

So, what happens when filamentous fungi colonize spacecrafts?

In the same room where astronauts used their treadmill to exercise their muscles, something different appeared on the walls: mold! This happened because the extra water coming from the astronaut’s sweaty clothes was being accumulated on the walls where clothes they were hung to dry, creating the perfect conditions for fungal growth: moisturized surface, a surface to attach to, and the controlled temperature of the ISS.

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Mold growing on a panel of the ISS where exercise clothes were hung to dry. Credit: NASA
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Moldy lettuce grown aboard the ISS as part of the Veggie plant growth facility. Credit: NASA.

Molds have yet another fascinating ability: they form biofilms. These biofilms are no more than complex structures of the fungi themselves (or other biofilm forming microorganisms), where different types of cells  (hyphae and spores) are mixed together in a goo of proteins and extracellular DNA.  This complex structure makes fungi more resistant to both mechanical and chemical stresses, such as antibiotics. On Earth fungal biofilms are found on our teeth, in industrial water systems or on medical instruments, such as catheters, being one of the main causes of infections. Fungal biofilms infections can happen in human lungs, and are hard to treat as biofilms have increased resistance to antibiotics.

In a spaceflight environment, an isolated habitat where all the air, food, water and waste management systems are connected, it is a great challenge to monitor and control fungal and other microbial contaminations. But space scientists are now acknowledging the importance of learning more about space microbes and their risks and threats, but also their opportunities. If you can find microbes everywhere, might as well put them to good use!

And that´s what we have been doing, for centuries. Bread, beer, cheese are only possible because of microorganisms. Right now, as we speak, molds are being used in biotechnology to produce vitamins, food preservatives and new, more efficient antibiotics. Why not do the same in space?

The future of space exploration depends largely on having Earth-independent resources, and microorganisms will definitely be an important part of it.