Space travel might permanently mutate E. coli, helping them to band together and survive. The longest study yet of bacteria in simulated microgravity found that their adaptations remained even when researchers tried to erase them.
A major concern for long-duration space flight is how the microorganisms who hitch a ride with us will adapt to the loss of gravity. Astronauts’ immune systems change in space, potentially making them more susceptible to infection, so if these bacteria become more virulent or antibiotic-resistant, they could pose a risk.
To assess that risk, Madhan Tirumalai at the University of Houston in Texas and his colleagues placed E. coli in a rotating vessel designed to simulate microgravity. They kept them there for 1,000 bacterial generations, much longer than in previous studies.
After giving the cells time to adapt to microgravity, the researchers combined them with another strain of E. coli that hadn’t been subjected to microgravity and allowed them to grow together. The adapted cells grew about three times as many colonies as the others.
Even after the cells were taken out of microgravity for up to 30 generations before being combined with the control strain, they maintained 72 per cent of their adaptive advantage, pointing to permanent mutations in the genes rather than merely a temporary adjustment.
“This study is broader in scope than previous ones on two counts,” says Jason Rosenzweig at Texas Southern University. “It’s looking at a much longer trajectory and it’s also interrogating the entire genome rather than specific subsets of genes.”
Genome sequencing revealed 16 mutations in the E. coli after microgravity exposure. “We are, in fact, seeing true genomic changes – permanent changes,” says team member George Fox at the University of Houston. We can see which genes are mutating, “but we don’t know what they’re doing exactly”.
However, some of the mutations occur on genes related to the ability to form biofilms, colonies of cells embedded in protective slime, says Tirumalai. Biofilms have been shown to make bacteria hardier in many situations, which may present a problem if one were to form, say, on a spaceship’s life support system.
“We need more of this kind of experiment, especially with human space flight gaining more traction in recent years,” says Tirumalai. E. coli is relatively innocuous, but the infection risk for astronauts on long missions could skyrocket if microgravity also makes more dangerous bacteria, such as salmonella, permanently hardier.
Luckily, the mutated cells from Tirumalai’s experiment were just as susceptible to antibiotics as before their exposure to microgravity. So even if microgravity turns bacteria into superbugs, antibiotics will remain a powerful line of defence.
Journal reference: NPJ Microgravity, DOI: 10.1038/s41526-017-0020-1
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