Where humans travel, bacteria will follow. If people are in space for any amount of time, bacteria are sure to thrive there so it's good to know that there are already researchers looking at how the environment within spaceships affects bacterial populations. Work done on planktonic colonies of bacteria has shown that they can become more virulent and grow faster once they leave earth, but more interestingly there are also changes to bacterial biofilms seen during space flight.

Biofilms are large bacterial colonies that can form on surfaces. They are particularly problematic in hospitals as the bacteria in the bottom of the biofilm are often protected from antibiotics. Biofilms are formed when free-swimming planktonic bacteria clump together, settle down, and coat themselves in slime.

Researchers on the Space Shuttle Atlantis cultured biofilms of the bacteria P. aeruginosa during spaceflight and characterised their properties. They found that the space grown bacteria produced bigger and thicker biomass structures, with more live cells involved. They also found that the structure of the biofilm differed. On earth biofilms form in either mushroom shapes (as shown above) or flat layers. In space they appear to form a series of upright columns with a canopy over the top.

The image below shows three slices through the biofilm on earth (on the left) and in space (on the right). The bacteria are all glowing green. The space bacteria are scattered widely in columns in the bottom slice, and form a dense canopy in the middle and top ones. On earth, each slicecontains around the same amount of bacteria. The biofilm in space is also taller.

The formation of these column and canopy shapes depends on the motility of the bacteria. When they are able to freely move about (propelled by tentacle-like flagella) the columns form. When bacterial motility is prevented by removing the flagella the columns don't form and instead the biofilm is made up of sticky layers as it is with non-motile bacteria on earth. The researchers propose that the column and canopy structure is formed by the elongation of the top of the mushrooms in reduced gravity to form a single flattened layer rather than disconnected caps. They also suggest that oxygen levels may play a part in determining the biofilm shape.

The behaviour of biofilms in space is important as plenty of biofilms have been found in spaceships where they cause problems with corrosion and blockage. Astronauts also have lowered immune systems in space, which makes the presence of any bacteria more dangerous. It's fascinating to see how the biofilm formation adapts to such an alien environment, but I'm sure research is also focussing on how to remove the biofilms completely.

---

Reference 1: Monroe D (2007) Looking for Chinks in the Armor of Bacterial Biofilms. PLoS Biol 5(11): e307. doi:10.1371/journal.pbio.0050307

Reference 2: Kim W, Tengra FK, Young Z, Shong J, Marchand N, et al. (2013) Spaceflight Promotes Biofilm Formation by Pseudomonas aeruginosa. PLoS ONE 8(4): e62437. doi:10.1371/journal.pone.0062437

Featured image: Earth rise as seen from the lunar surface. From the NASA Marshall Space Flight Center Collection