Research reveals plant pathogens reuse elements of phages for bacterial warfare

Bacteriophages, viruses that attack and destroy bacteria, are found throughout nature where they play an essential role in regulating microbial populations in ways that are not yet well understood.

New research from the University of Utah and University College London (UCL) has revealed that plant pathogenic bacteria are able to reuse parts of their own bacteriophages, or phages, to eliminate competing microbes.

These surprising findings suggest that these phage-derived elements could one day be harnessed as an alternative to antibiotics, according to Talia Karasov, an assistant professor in the University’s School of Biological Sciences. Titled “A phage tail-like bacteriocin suppresses competitors in metapopulations of pathogenic bacteria,” the study was published in Science.

This result was not what she expected when she embarked on this research with an international team of scientists.

Microbial pathogens are ubiquitous, but they only sicken humans, other animals or plants a fraction of the time, according to Karasov, whose primary research interest is interactions between plants and microbial pathogens. . The Karasov lab seeks to understand the factors that lead to diseases and epidemics rather than controlling pathogens.

For its previous research, the lab examined how a particular bacterial pathogen, Pseudomonas viridiflava, manifests itself in agricultural and wild environments. On cropland, they found, one variant would spread widely throughout a crop field and become the dominant microbe present. But that wasn’t the case on the wastelands, which prompted Karasov to find out why.

“We find that no single lineage of bacteria can dominate. We wondered if phages, the pathogens of our disease-causing bacteria, could prevent the spread of single lineages – perhaps phages killed some strains and not others. “That’s where our study started, but that’s not where it ended up,” Karasov said.

“We looked at the genome of plant pathogenic bacteria 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 reused it to fight other bacteria , now using it to kill competing bacteria.

According to his study, the pathogen acquires elements from phages in the form of non-self-replicating clusters of repurposed phages called tailocins, which penetrate the outer membranes of other pathogens and kill them.

After discovering this ongoing war in bacterial populations of pathogens, the Karasov lab and Hernán Burbano’s lab at UCL mined the genomes of modern and historical pathogens to determine how bacteria evolve to target each other.

“You can imagine an arms race between bacteria where they try to kill each other and develop resistance to each other over time,” Burbano said. “The herbarium samples from the past 200 years that we analyzed have opened a window into this arms race, providing insight into how bacteria escape destruction by their competitors.”

Extraction of herbarium specimens for their microbial DNA

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

For phage research, Burbano analyzed historical specimens of Arabidopsis thaliana, a mustard family plant commonly known as thale cress, collected in southwest Germany, comparing them and the microbes that They were home to plants growing today in the same part of Germany.

“We found that all historical tailocins were present in our current dataset, suggesting that evolution has maintained the diversity of tailocin variants on a century-long scale,” he said. “This likely indicates a finite set of possible resistance/susceptibility mechanisms within our studied bacterial population.

Lead author Talia Backman wonders whether tailocins could help solve the looming antibiotic resistance crisis seen in harmful bacteria that infect humans.

“As a society, we are in dire need of new antibiotics, and tailocins have potential as new antimicrobial treatments,” said Backman, a graduate student in the Karasov lab.

“Although tailocins have previously been found in other bacterial genomes and studied in the laboratory, their impact and evolution in wild bacterial populations was not known. The fact that we discovered that these wild plant pathogens have “All tailocins and that these tailocins evolve to kill neighboring bacteria shows how important they can be in nature.”

Like most pesticides, many of our antibiotics were developed decades ago to kill a wide range of pests, both harmful and beneficial to human and plant health. Talocins, on the other hand, have greater specificity than most modern antibiotics, killing only a few selected strains of bacteria, suggesting they could be deployed without wasting entire biological communities.

“This is basic research at this stage, not yet ready to be applied, but I think there is good potential that it could be adapted to treat infections,” said Karasov.

“As a society, we have used uniform, broad-spectrum treatments in how we treat both pests in agriculture and pathogenic bacteria in humans. The Specificity of Tailocin Killing is a way you could imagine doing more finely tuned treatments.”

University College London, the Max Planck Institute of Biology, the Complex Carbohydrate Research Center Analytical Services and Training Lab at the University of Georgia, New York University, the Department of Biochemistry at the University of Georgia and Lawrence participated in the research with the University’s School of Biological Sciences. Berkeley National Laboratory.