Bacteriophages: How bacteria harness viruses to do their bidding

Bacteriophages, viruses that attack and destroy bacteria, are ubiquitous in nature. They play a vital role in regulating microbial populations, although their mechanisms are not yet fully understood.

Recent research has uncovered that plant bacterial pathogens can repurpose elements of their bacteriophages, or phages, to eliminate competing microbes. This discovery opens new possibilities for alternative antibiotics.

Bacteriophage research

A collaborative study led by the University of Utah and University College London (UCL) has revealed that plant bacterial pathogens utilize bacteriophage-derived elements to combat rival bacteria.

According to Talia Karasov, an assistant professor at the University of Utah’s School of Biological Sciences, these findings could lead to the development of new antimicrobial treatments.

This unexpected result emerged from research focused on the interactions between plants and microbial pathogens.

The primary interest was understanding what keeps these pathogens in check and what causes them to lead to sickness and epidemics.

Investigating pathogen behavior

The research team examined the behavior of the bacterial pathogen Pseudomonas viridiflava in both agricultural and wild environments.

On cultivated land, one variant would dominate a crop field, but this was not the case in uncultivated areas. This discrepancy prompted further investigation.

“We see that no single lineage of bacteria can dominate. We wondered whether phages, the pathogens of our bacterial pathogens, could prevent single lineages from spreading,” Karasov explained.

“Maybe phages were killing some strains and not others. That’s where our study started, but that’s not where it ended up.”

Bacteriophages turned into bacterial weapons

The research involved analyzing the genomes of plant bacterial pathogens to identify which bacteriophages were infecting them.

It wasn’t the phage itself that was interesting, but rather how the bacteria had repurposed it. The bacteria were using bacteriophage elements, now called tailocins, to kill competing bacteria.

The study, published in Science, showed that these non-self-replicating clusters of repurposed phage elements penetrate the outer membranes of other pathogens, killing them.

This ongoing bacterial warfare prompted the researchers to mine the genomes of modern and historical pathogens to understand how bacteria evolve to target one another.

“You can imagine an arms race between the bacteria where they’re trying to kill each other and trying to evolve resistance to one another over time,” said Hernan Burbano, a researcher from UCL.

“The herbarium samples from the past 200 years that we analyzed provided a window into this arms race, giving insight into how bacteria evade being killed by their competitors.”

Historical Insights from herbarium specimens

The UCL lab has pioneered the use of herbarium specimens to explore the evolution of plants and their microbial pathogens.

By sequencing the genomes of both host plants and the microbes they harbored at the time of collection over a century ago, the researchers gained valuable insights.

For the phage research, historical specimens of Arabidopsis thaliana, commonly known as thale cress, collected in southwestern Germany, were compared to modern plants from the same region.

The analysis revealed that all historical tailocins were present in the present-day dataset, suggesting that evolution has maintained the diversity of tailocin variants over a century.

“This likely indicates a finite set of possible resistance/sensitivity mechanisms within our studied bacterial population,” said Burbano.

Tailocins and antibiotic resistance

The lead author, Talia Backman, a graduate student in the Karasov lab, believes that tailocins could help address the growing issue of antibiotic resistance.

“We as a society are in dire need of new antibiotics, and tailocins have potential as new antimicrobial treatments,” Backman said. “While tailocins have been found previously in other bacterial genomes and studied in lab settings, their impact and evolution in wild bacterial populations were not known.”

The fact that we found these wild plant pathogens all have tailocins and these tailocins are evolving to kill neighboring bacteria shows how significant they may be in nature.

Tailocins offer greater specificity than most modern antibiotics, targeting only a select few strains of bacteria. This specificity suggests they could be used without harming entire biological communities.

“This is basic research at this point, not yet ready for application, but I think there is good potential that this could be adapted for treating infection,” said Talia Karasov.

“We as a society have, in how we treat both pests in agriculture and bacterial pathogens in humans, used uniform and broad-spectrum treatments. The specificity of tailocin killing is a way that you could imagine doing more finely tailored treatments.”

Continuing the fight against antibiotic resistance

In summary, the research led by Talia Karasov and Hernán Burbano unveils a fascinating aspect of the microbial world, where bacteria engage in a relentless arms race using repurposed phage elements called tailocins.

This discovery sheds light on the complex interactions between bacteria and their phages while opening up exciting possibilities for the development of targeted antibiotics.

As scientists continue to explore the potential of tailocins as a new class of antimicrobial treatments, we move closer to a future where more precise and effective strategies can be employed to combat the growing threat of antibiotic resistance.

The findings of this study serve as a reminder of the untapped potential that lies within the intricate relationships between microorganisms, and how understanding these interactions can lead to groundbreaking advancements in the fight against harmful bacteria.

The full study was published in the journal Science.

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