Bacteria onboard the ISS are not mutating into superbugs harmful to humans, they are simply adapting to their stressful lives and trying to survive.
New research from Northwestern University has found that although bacteria isolated from the ISS did contain different genes than their Earth living counterparts, those differing genes did not make them more dangerous to humans.
"There has been a lot of speculation about radiation, microgravity and the lack of ventilation and how that might affect living organisms, including bacteria," said Northwestern's Erica Hartmann, who led the study.
"These are stressful, harsh conditions. Does the environment select for superbugs because they have an advantage? The answer appears to be 'no.'"
Understanding space microbes critical for deep space exploration
As the possibility of humans traveling to Mars becomes more and more real the interest in space microbes increases.
"People will be in little capsules where they cannot open windows, go outside or circulate the air for long periods of time," said Hartmann.
"We're genuinely concerned about how this could affect microbes."
The ISS hosts thousands of different earth borne microbes which have traveled to space on cargo or with astronauts.
Data on some of these microbes isolated from the ISS is available through a public database maintained by The National Center for Biotechnology Information.
Hartmann's and her team used this data to compare the strains of Staphylococcus aureus and Bacillus cereus on the ISS to those on Earth.
ISS bacteria determined to survive
Bacteria are often drawn to living on human skin due to its warmth and rich supply of oil and organic chemicals. When bacteria are shed from the skin on to cold surfaces they can undergo a period of stress.
To adapt to their new environment only bacteria containing advantageous genes for living under that stress are selected before they mutate.
In the example of the ISS, only the genes that allowed the bacteria to continue to thrive under their new stressful environment were selected.
"Based on the genomic analysis, it looks like bacteria are adapting to live -- not evolving to cause disease," said Ryan Blaustein, a postdoctoral fellow in Hartmann's laboratory and the study's first author.
"We didn't see anything special about antibiotic resistance or virulence in the space station's bacteria."
This is good news for astronauts and space colonizers in general, but the studies' authors were quick to point out that sick astronauts will still cause disease to spread.
"Everywhere you go, you bring your microbes with you," Hartmann said.
"Astronauts are exceedingly healthy people. But as we talk about expanding space flight to tourists who do not necessarily meet astronaut criteria, we don't know what will happen. We can't say that if you put someone with infection into a closed bubble in space that it won't transfer to other people. It's like when someone coughs on an airplane, and everyone gets sick."