Bacteriophages use ‘selfish genetic elements’ as weapons

For many years, small segments of DNA known as “selfish genetic elements” were considered nonessential, existing only to propagate themselves. 

However, researchers at the University of California San Diego (UCSD) have discovered that these elements may play a significant role in the competition among organisms. 

Focus of the study

“Introns containing homing endonucleases are widespread in nature and have long been assumed to be selfish elements that provide no benefit to the host organism. These genetic elements are common in viruses, but whether they confer a selective advantage is unclear,” noted the researchers.

The findings, published in the journal Science, reveal that the genetic elements, specifically mobile introns in bacteriophages (phages), can indeed confer competitive advantages to their hosts.

“In this work, we studied intron-encoded homing endonuclease gp210 in bacteriophage ΦPA3 and found that it contributes to viral competition by interfering with the replication of a co-infecting phage, ΦKZ,” wrote the study authors.

Bacteriophages outcompete rival viruses 

Bacteriophages, viruses that infect bacteria, are the most abundant organisms on Earth. The research team discovered that mobile introns act as tools for phages, enabling them to outcompete rival viruses. 

“This is the first time a selfish genetic element has been demonstrated to confer a competitive advantage to the host organism it has invaded,” said co-lead author Erica Birkholz, a postdoctoral scholar at UCSD.

Weaponized genetic elements 

Focusing on “jumbo” phages, the researchers analyzed the dynamics within bacterial cells co-infected by two phages. They observed how an enzyme called endonuclease from one phage’s mobile intron disrupts the DNA of competing phages. 

This enzyme cuts into the rival phage’s genome, preventing it from effectively assembling its progeny. As Birkholz noted, “this weaponized intron endonuclease gives a competitive advantage to the phage carrying it.”

The study highlights the importance of these findings in understanding the evolutionary arms race among viruses. 

“We were able to clearly delineate the mechanism that gives an advantage and how that happens at the molecular level,” explained co-lead author Chase Morgan, a graduate student at the same university. “This incompatibility between selfish genetic elements becomes molecular warfare.”

Broader implications of the research 

The implications of this research extend to phage therapy, which is increasingly used to combat antibiotic-resistant bacteria. The insights gained could improve the design of phage cocktails, enhancing their efficacy. 

“The phages in this study can be used to treat patients with bacterial infections associated with cystic fibrosis,” said senior author Joe Pogliano, a professor of biological sciences at UCSD. 

“Understanding how they compete with one another will allow us to make better cocktails for phage therapy.”

In essence, this study not only redefines our understanding of selfish genetic elements but also provides a deeper insight into viral competition and potential therapeutic applications. 

The findings challenge the previous notion of these DNA segments being mere genetic hitchhikers, showing they can significantly impact host survival and evolution.

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