Viruses Behave Totally Differently in Space and It Could Help Us Treat Superbugs on Earth

Bacteria and viruses are locked in a slow motion battle aboard the ISS that looks nothing like life on the ground.

Bacteriophages — viruses that prey on bacteria — are nature’s tiniest predators. On Earth, their lives are shaped by an ordinary physics engine we rarely think about: gravity-driven mixing. Liquids circulate, nutrients move, microbes bump into one another, and phages stumble into susceptible cells.

Take gravity away and you get a microbial world where particles drift, convection fades, and the odds of a productive collision change. Yet even in the near-weightlessness of the International Space Station (ISS), viruses called phages can still infect bacteria, a new PLOS Biology study reports. But microgravity seems to change the pace and rules of their back-and-forth battle, nudging both the virus and the bacteria to evolve in different ways than they do on Earth.

Phages vs bacteria in space

The team focused on a classic pairing: T7, a well-studied phage, and Escherichia coli BL21, a lab strain commonly used in biology. They prepared matched sets of sealed cryovials on Earth, froze them, then incubated one set in microgravity on the ISS and the other on the ground under similar conditions. Short-term samples were run for one, two, and four hours; a long-term set ran for 23 days.

On Earth, infection became obvious between two and four hours. Phage counts rose sharply while bacterial counts dropped. In microgravity, the short-term samples showed no phage surge at 1–4 hours. Yet after 23 days, T7 levels climbed by about four orders of magnitude — evidence that infection and replication did occur, just on a much slower timetable.

The data also hinted at a familiar outcome in an unfamiliar setting: resistance. Bacteria persisted at day 23 in both environments, consistent with phage-resistant survivors emerging over time.

“Space fundamentally changes how phages and bacteria interact: infection is slowed, and both organisms evolve along a different trajectory than they do on Earth,” the authors said. “By studying those space-driven adaptations, we identified new biological insights that allowed us to engineer phages with far superior activity against drug-resistant pathogens back on Earth.”

With less mixing, cells can wind up sitting in a little pocket of their own waste while not getting a steady supply of fresh nutrients. Past studies also suggest that in space-like conditions, microbes can change their outer coating, form thicker “slimy” communities called biofilms, and dial their stress responses up or down a notch. If the bacterial surface shifts, phages may have a harder time locking on since the docking points they use to attach can change.

Once the long incubation was over, the researchers compared genomes from Earth and ISS samples. Both phages and bacteria accumulated new mutations, but the pattern differed, suggesting selection pressures weren’t the same even though the organisms were.

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What this means for spaceflight—and for medicine

For long-duration missions, microbial behavior is not a back-burner issue. Astronauts live in a closed habitat where bacteria and viruses share surfaces, air, water systems, and the human body. Understanding whether phages can keep bacterial populations in check — or whether bacteria evolve differently in orbit — matters for managing microbial communities in spacecraft.

For Earth, the result feeds into a growing interest in phage therapy, especially as antibiotic resistance spreads. This study doesn’t prove a ready-to-use treatment, but it suggests microgravity can act like a novel evolutionary filter — one that helps researchers discover receptor-binding solutions that standard lab conditions might miss.

Overall, this study highlights the potential for phage research aboard the ISS to reveal new insights into microbial adaption, with potential relevance to both space exploration and human health.