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Scientists brought bacteria and phages, that is viruses that infect bacteria, aboard the ISS to study their evolution. . | Credit: International space station (dima_zel/Getty Images); E.coli (Shutterstock)
Bacteria and the viruses that infect them, called phages, are locked in an evolutionary arms race. But that evolution follows a different trajectory when the battle takes place in microgravity, reveals a study carried out on board the International Space Station (ISS).
As bacteria and phages evolve, bacteria evolve better defenses to survive while phages evolve new ways to penetrate those defenses. The new study, published on January 13 in the journal PLOS Biologydetails how that fight plays out in space and reveals insights that could help us design better drugs for antibiotic-resistant bacteria on Earth.
In the study, researchers compared populations of E. coli infected with a beech known as T7. One set of microbes was incubated aboard the ISS, while identical control groups were grown on Earth.
Analysis of space station samples showed that microgravity fundamentally changed the speed and nature of phage infection.
While the phages were still able to successfully infect and kill bacteria in space, the process took longer than it did in the Earth samples. In an previous studythe same researchers hypothesized that the infection cycles in microgravity would be slower because fluids do not mix as well in microgravity as they do in Earth’s gravity.
“This new study validates our hypothesis and expectation,” said the study’s lead author. Srivatsan Ramanassociate professor in the Department of Biochemistry at the University of Wisconsin-Madison.
On Earth, the fluids bacteria and viruses exist in are constantly being stirred by gravity – hot water rises, cold water sinks, and heavier particles settle to the bottom. This keeps everything moving and colliding with each other.
In space, there is no stirring; everything just floats me. So because the bacteria and phages weren’t bumping into each other as often, the phages had to adapt to a much slower pace of life and become more efficient at latching onto passing bacteria.
Experts think that understanding this alternative form of phage evolution could help them develop new phage therapies. These emerging treatments for infections use phages to kill bacteria or make microbes more vulnerable to traditional antibiotics.
“If we can work out what phages are doing at the genetic level to adapt to the microgravity environment, we can apply that knowledge to experiments with resistant bacteria,” Nicol Caplina former astrobiologist at the European Space Agency who was not involved in the study, told Live Science in an email. “And this could be a positive step in the race to optimize antibiotics on Earth.”
Whole-genome sequencing revealed that both bacteria and phages on the ISS have accumulated distinctive genetic mutations not observed in samples on Earth. Space-based viruses have accumulated specific mutations that have enhanced their ability to infect bacteria, as well as their ability to bind to bacterial receptors. At the same time, the E. coli they developed mutations that protect against phage attacks – by tweaking their receptors, for example – and improved their survival in microgravity.
Then, the researchers used a technique called deep mutational scanning to examine the changes in the proteins that bind to the viruses’ receptors. They found that adaptations driven by the unique cosmic environment could have practical applications back home.
When the phages were transported back to Earth and tested, the space-adapted changes in their receptor-binding protein resulted in increased activity against E. coli strains that commonly cause urinary tract infections. These strains are typically resistant to T7 phage.
“It was a serendipitous find,” Raman said. “We did not expect that the [mutant] phages we identified on the ISS kill pathogens on Earth.”
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“These results show how space can help us improve the activity of phage therapies,” he said. Charlie Moassistant professor in the Department of Bacteriology at the University of Wisconsin-Madison who was not involved in the study.
“However,” added Mo, “we need to consider the cost of sending phages into space or simulating microgravity on Earth to achieve these results.”
In addition to helping fight infections in Earthbound patients, the research could help yield more effective phage therapies for use in microgravity, Mo suggested. “This could be important for the health of astronauts in long-term space missions – for example, missions to the moon or Mars, or long stays in the ISS.”