Microbes stranded in the International Space Station (ISS) are not mutating into dangerous, antibiotic-resistant superbugs despite its seemingly harsh conditions, scientists have found.
While the team from Northwestern University in the US found that the bacteria isolated from the ISS did contain different genes than their Earthling counterparts, those genes did not make the bacteria more detrimental to human health.
The bacteria are instead simply responding, and perhaps evolving, to survive in a stressful environment.
"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 Erica Hartmann, who led the study published in the journal mSystems.
"These are stressful, harsh conditions. Does the environment select for superbugs because they have an advantage? The answer appears to be 'no'," Hartmann said.
As the conversation about sending travellers to Mars gets more serious, there has been an increasing interest in understanding how microbes behave in enclosed environments, researchers said.
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"People will be in little capsules where they cannot open windows, go outside or circulate the air for long periods of time. We're genuinely concerned about how this could affect microbes," said Hartmann.
The ISS houses thousands of different microbes, which have travelled into space either on astronauts or in cargo.
Researchers compared the strains of Staphylococcus aureus and Bacillus cereus on the ISS to those on Earth. Found on human skin, S aureus contains the tough-to-treat MRSA strain. B cereus lives in soil and has fewer implications for human health.
"Bacteria that live on skin are very happy there. Your skin is warm and has certain oils and organic chemicals that bacteria really like," said Hartmann.
"When you shed those bacteria, they find themselves living in a very different environment. A building's surface is cold and barren, which is extremely stressful for certain bacteria," he said.
To adapt to living on surfaces, the bacteria containing advantageous genes are selected for or they mutate. For those living on the ISS, these genes potentially helped the bacteria respond to stress, so they could eat, grow and function in a harsh environment.
"Based on 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.
"We didn't see anything special about antibiotic resistance or virulence in the space station's bacteria," Blaustein said.
Although this is good news for astronauts and potential space tourists, researchers are careful to point out that unhealthy people can still spread illness on space stations and space shuttles.
"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," Blaustein said.
"We can't say that if you put someone with an 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," he said.