This petri dish contains fungus samples collected from the International Space Station. (Credit: NASA/JPL)

Anywhere humans go, we bring companions along, in the form of bacteria and mold. Some of them, like gut bacteria, are essential for healthy living. Others are mere tagalongs. As hospitals well know, even the spaces meant to be most clean still teem with microbial life, and the International Space Station is no exception.

Astronauts have been cataloging the presence of microbes in sp