Space is a dangerous place. Astronauts are wrapped up in layers of protection that regulate pressure, temperature, and oxygen. This protection has been developed through decades of medical research and testing, just to keep astronauts alive. The main space hazards that astronauts need to be protected from are rapid temperature fluctuations from -120°C to +120°C (-184°F to 248°F), atmosphere so thin it’s essentially a vacuum, and several types of radiation capable of destroying human cells, tissues, and organs. How, then, are tiny, relatively unsophisticated bacteria able to survive in space without any of these protective measures? The Biofilm Organisms Surfing Space (BOSS) study led by Dr. Petra Rettberg aims to understand just that.
The European Space Agency’s EXPOSE facility is mounted outside the International Space Station and allows for the exposure of biological and chemical samples to the environment of space while recording data during exposure. Scientists performing the BOSS study used the EXPOSE facility to investigate a specific bacterial strain called Gloeocapsa, which normally lives in the surface layer of limestone cliffs in Devon, England. The experiment was designed to study whether biofilm (or grouped) Gloeocapsa were able to survive better in space compared to free-floating, single Gloeocapsa. Furthermore, some bacterial samples were directly exposed to the space environment while others were partially shielded to simulate a Martian environment.
Bacterial growth was recorded after both 3 months and 9 months of exposure. After 531 days, the bacterial samples were brought back inside the International Space Station. Upon their return to Earth, the BOSS scientists examined the bacterial samples using a variety of chemical and biological laboratory techniques to assess the structural and viability differences between experimental groups. This included culturing the recovered samples to see if they could be revived, staining to visualize live versus dead cells, enzymatic activity, and damage to cell membranes. They also performed a visual inspection of the samples using high resolution electron microscopy.
The collective analyses showed that the biofilm samples had increased viability compared to the free-floating bacteria. This was especially true in the simulated Martian environment, where the samples were partially shielded. An unexpected second conclusion arose from this experiment. Although the scientists aimed to only study the protection of Gloeocapsa, they found a second species that “hitchhiked” in the biofilms and benefited from the protective environment of the Gloeocapsa biofilms. This finding shows that in addition to protecting organisms of their own species, biofilms also aid in interspecies protection through forming safe micro-habitats.
So why exactly are these findings a big deal? The BOSS study reveals important considerations for planetary protection as well as for protecting the health of astronauts in space. Planetary protection refers to the practice of keeping planets that we visit free from contamination with Earth-based life. Since zero contamination is a very lofty goal, scientists have been cataloging which organisms are able to survive on the surface on the International Space Station. These could potentially contaminate any planets we may visit. The hitchhiker bacterial strain in the BOSS study reveals the issue that even organisms that cannot survive the harshness of space themselves, may be able to survive long enough to contaminate planets by living in safe microhabitats inside biofilms of other organisms. Furthermore, since the human immune system is compromised during spaceflight and access to medical resources is severely limited, understanding bacterial pathogenesis and survival is key in sustaining the health of astronauts on long duration missions.