Bacteriophages : Nature's bacterial killers

June 14, 2024
Above: Talia Karasov

Bacteriophages, viruses that attack and destroy bacteria, are everywhere in the natural world where they play a vital role in regulating microbe populations in ways that are not yet well understood.

New research led by the University of Utah and University College London (UCL) has found that plant bacterial pathogens are able to repurpose elements of their own bacteriophages, or phages, to wipe out competing microbes. These surprise findings suggest such phage-derived elements could someday be harnessed as an alternative to antibiotics, according to Talia Karasov, an assistant professor in the U’s School of Biological Sciences.

This result was hardly what she expected to find when she embarked on this research with an international team of scientists. Microbial pathogens are all around, but only a fraction of the time do they sicken humans, other animals or plants, according to Karasov, whose primary research interest is in interactions between plants and microbial pathogens. The Karasov lab is seeking to understand the factors that lead to sickness and epidemics versus keeping the pathogens in check.

“We see that no single lineage of bacteria can dominate. We wondered whether the phages, the pathogens of our bacterial pathogens, could prevent single lineages from spreading – maybe phages were killing some strains and not others. That’s where our study started, but that’s not where it ended up,” Karasov said. “We looked in the genomes of plant bacterial pathogens to see which phages were infecting them. But it wasn’t the phage we found that was interesting. The bacteria had taken a phage and repurposed it for warfare with other bacteria, now using it to kill competing bacteria.”

A thale cress specimen collected in 1866 in Germany and preserved in a herbarium in Tubingen. Credit: Burbano lab, University College London.

Mining herbarium specimens for their microbial DNA

Burbano has pioneered the use of herbarium specimens to explore the evolution of plants and their microbial pathogens. His lab sequences the genomes of both host plants and those of the microbes associated with the plant at the time of collection more than a century ago.

For the phage research, Burbano analyzed historical specimens of Arabidopsis thalianaa plant from the mustard family commonly called thale cress, collected in southwestern Germany, comparing them and the microbes they harbored to plants growing today in the same part of Germany. Lead author Talia Backman wonders if tailocins could help solve the impending crisis in antibiotic resistance seen in harmful bacteria that infect humans.

“We as a society are in dire need of new antibiotics, and tailocins have potential as new antimicrobial treatments,” said Backman, a graduate student in the Karasov lab. “While tailocins have been found previously in other bacterial genomes, and have been studied in lab settings, their impact and evolution in wild bacterial populations was not known. The fact that we found that these wild plant pathogens all have tailocins and these tailocins are evolving to kill neighboring bacteria shows how significant they may be in nature.”

Discover the full story behind bacteriophages and their antibiotic potential by Brian Maffly at @The U. More on this story at