Experiments conducted aboard the International Space Station are revealing an unexpected ally in the fight against antimicrobial resistance: bacteriophages shaped by microgravity.
New findings suggest that viruses evolved in near-weightless conditions can acquire genetic changes that make them more effective at infecting and killing bacterial pathogens once returned to Earth.
The study, published in PLOS Biology, offers rare insight into how radically different environments influence virus–host evolution, and how those changes might be harnessed for future phage-based therapies.
A different evolutionary battlefield
Bacteria and bacteriophages are locked in a constant evolutionary struggle. As bacteria develop defences, phages counter with new strategies to bind, infect, and replicate. On Earth, this interaction unfolds in fluids constantly mixed by gravity, convection, and sedimentation.
In microgravity, those physical rules change.
To explore the consequences, researchers cultured Escherichia coli alongside a well-characterised bacteriophage aboard the ISS, while identical cultures were grown under standard laboratory conditions on Earth. The goal was not to enhance phage performance, but to observe how evolution proceeds when gravity is largely removed from the equation.
Slower infections, stronger selection
Analysis of the space-grown samples showed that phage infections progressed more slowly in microgravity. With fewer random collisions between viruses and bacteria, successful infection events became rarer, placing intense selective pressure on phages to improve their ability to attach to bacterial cells.
Genomic sequencing revealed that both bacteria and phages accumulated mutations unique to the space environment. For phages, many of these changes occurred in genes associated with receptor binding, the molecular “handshake” that allows a virus to latch onto a bacterial surface.
At the same time, bacterial populations evolved their own counter-measures, modifying surface receptors and stress-response pathways to survive both infection and the demands of microgravity.
Back on Earth, an unexpected advantage
The most striking result emerged only after the experiment ended.
When space-evolved phages were brought back to Earth and tested against clinically relevant E. coli strains, they showed enhanced killing activity, including against strains that are typically less susceptible to the original phage.
This was not the primary aim of the experiment, but it highlights how evolution in extreme environments can reveal adaptive routes rarely explored under normal laboratory conditions.
In effect, microgravity acted as an evolutionary filter, favouring viral variants that bind more efficiently and infect more decisively.
Implications for phage therapy and AMR
Phage therapy is gaining renewed interest as antibiotic resistance continues to rise globally. One of the major challenges is identifying or engineering phages capable of targeting resistant bacterial strains.
These findings suggest that environment-driven evolution, whether in space or in carefully designed Earth-based systems, could be used to expand the functional diversity of therapeutic phages.
Rather than relying solely on genetic engineering, researchers may be able to steer natural evolutionary processes toward clinically useful outcomes, producing phages with improved infectivity, broader host range, or enhanced stability.
Not a shortcut, but a blueprint
Sending microbes into space is expensive and impractical as a routine tool. However, the value of this research lies less in the destination and more in the principle.
By understanding why microgravity drives these adaptations, altered fluid dynamics, reduced mixing, and prolonged contact times, scientists can begin to recreate similar selective pressures in ground-based systems, such as rotating wall vessels or microfluidic platforms.
The same insights may also prove critical for astronaut health, as future long-duration missions will require reliable strategies to control infections in space environments.
Reporting note: This article is based on a peer-reviewed study published in PLOS Biology.
