In new experiments aboard the International Space Station (ISS), microbiologists from the University of Wisconsin-Madison and Rhodium Scientific Inc. have discovered that the near-weightless environment of space can significantly reshape how bacteriophages — viruses that infect bacteria — interact with their hosts.
The International Space Station is seen with Earth in the background. Image credit: NASA.
In a systematic study of bacteriophage-host dynamics in microgravity, University of Wisconsin-Madison researcher Phil Huss and his colleagues examined the interaction between T7 phage and Escherichia coli bacteria during incubation on the orbiting laboratory.
Their experiments revealed that microgravity delayed the virus’ ability to infect and kill the bacteria but did not permanently prevent infection.
Under terrestrial conditions, T7 phages normally infect and lyse Escherichia coli within 20 to 30 minutes.
But in microgravity, the researchers observed no measurable bacteriophage growth during the first hours of incubation.
After 23 days, however, bacteriophages had successfully propagated and reduced bacterial populations, indicating bacteriophage activity eventually overcame the initial delay caused by the microgravity environment.
The physical characteristics of microgravity — including reduced fluid convection and altered bacterial physiology — are believed to change how bacteriophage particles encounter and infect their bacterial hosts.
In the absence of gravity, the normal mixing of fluids that brings viral particles into contact with bacteria is disrupted, potentially slowing early stages of infection.
To better understand the evolutionary and molecular consequences of these altered interactions, the scientists sequenced the genomes of both bacteriophages and bacteria after long-term incubation.
They found numerous newly emerged mutations in both viral and bacterial genomes, indicating that both organisms adapted to the conditions they encountered.
Distinct patterns of mutations were seen in microgravity compared with those evolved under Earth gravity, suggesting that the space environment imposed unique selective pressures on both bacteriophage and host.
Further analyses focused on the bacteriophage’s receptor binding protein, a key element that determines how effectively a virus recognizes and infects its bacterial target.
Using deep mutational scanning, the authors identified substantial differences in the mutational landscape of this protein between microgravity and terrestrial experiments, reflecting underlying changes in host adaptation and selection.
In a notable finding, they used libraries of receptor binding protein variants shaped by microgravity selection to produce bacteriophage variants that were more effective at infecting certain drug-resistant strains of Escherichia coli on Earth — a result that highlights the potential for space-based research to inform terrestrial biotechnology.
“Our study offers a preliminary look at how microgravity influences phage-host interactions,” the researchers concluded.
“Exploring phage activity in non-terrestrial environments reveals novel genetic determinants of fitness and opens new avenues for engineering phages for terrestrial use.”
“The success of this approach helps lays the groundwork for future phage research aboard the ISS.”
The study appears online in the journal PLoS Biology.
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P. Huss et al. 2026. Microgravity reshapes bacteriophage-host coevolution aboard the International Space Station. PLoS Biol 24 (1): e3003568; doi: 10.1371/journal.pbio.3003568
