Microbiologists from the University of Wisconsin-Madison and Rhodium Scientific have unveiled a groundbreaking discovery aboard the International Space Station (ISS). Their latest experiment reveals that the unique near-weightless environment of space significantly alters the interactions between bacteriophages (viruses that target bacteria) and their hosts.

The International Space Station, with Earth in the background. Image credit: NASA.

In this detailed study focused on bacteriophage-host dynamics in microgravity, University of Wisconsin-Madison researcher Phil Huss and his team analyzed the interaction of T7 phages with Escherichia coli bacteria cultivated in an orbiting laboratory.

The experiments highlighted that while microgravity slows the infection rate of viruses, it does not permanently inhibit their ability to infect.

Under normal Earth conditions, T7 phages typically infect and lyse Escherichia coli within 20 to 30 minutes.

However, in the microgravity setting, no measurable growth of the bacteriophages was observed during the initial hours of culture.

After 23 days, the bacteriophage started to grow normally, effectively reducing the bacterial count. This suggests that bacteriophage activity eventually overcame the initial delays caused by the microgravity environment.

Factors unique to microgravity, such as disrupted fluid convection and changes in bacterial physiology, appear to influence how bacteriophage particles encounter and infect bacterial hosts.

In the absence of gravity, the natural mixing of fluids that typically facilitates virus-bacteria contact may be hindered, thereby slowing down the initial infection stages.

To delve deeper into the evolutionary and molecular consequences of these altered interactions, researchers sequenced the genomes of both bacteriophages and bacteria post long-term culture.

The analysis revealed numerous emerging mutations in the genomes of both organisms, indicating adaptation to their unique conditions.

Intriguingly, different mutation patterns were identified in microgravity compared to those evolving under Earth’s gravity, highlighting that the space environment exerts distinct selective pressures on both bacteriophages and their bacterial hosts.

Further scrutiny focused on the bacteriophage’s receptor-binding proteins, essential for recognizing and infecting bacterial cells effectively.

Through a deep mutational scan, significant differences in the mutational profiles of these proteins were observed between microgravity and ground-based experiments, reflecting fundamental changes in adaptive capabilities.

In a remarkable find, the researchers utilized a library of receptor-binding protein variants selected in microgravity to create bacteriophage variants that are more efficient at infecting specific drug-resistant strains of Escherichia coli on Earth. This underscores the potential of space-based research to inform biotechnology.

“Our study provides initial insights into how microgravity influences phage-host interactions,” the researchers concluded.

“Investigating phage activity in non-terrestrial settings unveils new genetic determinants of fitness, paving the way for innovative phage engineering on Earth.”

“The success of this research will establish a foundation for future phage investigations aboard the ISS.”

For more details, refer to the study published in the online journal PLoS Biology.

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P. Hass et al. 2026. Microgravity reshapes bacteriophage-host coevolution on the International Space Station. PLoS Biol 24 (1): e3003568; doi: 10.1371/journal.pbio.3003568