Not So Selfish After All For Selfish Genetic Elements of Viruses

Some curious fragments of DNA hidden within genomes across all life forms have historically been overlooked, as they appeared to have no role in survival competition—until now. Phage viruses, that used regularly to combat against antibiotic resistance, gain an advantage with the help of these curious fragments or selfish genetic elements of viruses by inhibiting a competitor’s ability to reproduce.

Date	July 4, 2024
Source	University of California – San Diego
Summary	Certain DNA segments have been identified as selfish genetic elements of viruses because they were thought not to contribute to a host organism’s survival. However, researchers have now discovered that these elements have been weaponized, playing a crucial role by inhibiting a competitor’s ability to reproduce. Published in the journal Science.

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Discovery of Selfish Genetic Elements of Viruses

• Decades ago, biologists noted the existence of selfish genetic elements but could not identify any role they played in aiding the host organism’s survival and reproduction.
• Research by scientists at the University of California San Diego has uncovered new evidence suggesting that these DNA elements might not be so selfish after all. Instead, they seem to play a significant role in the interactions between competing organisms.
• In this new study, which focused on “jumbo” phages, the researchers examined the dynamics when two phages co-infect a single bacterial cell and compete with each other.
• They closely studied endonuclease, an enzyme that acts as a DNA-cutting tool. The endonuclease from one phage’s mobile intron interferes with the genome of the competing phage.
• This enzyme cuts an essential gene in the competitor’s genome, sabotaging its ability to properly assemble its progeny and reproduce.
• This weaponized intron endonuclease gives a competitive advantage to the phage carrying it.
• “We were able to clearly delineate the mechanism that gives an advantage and how that happens at the molecular level,” said Chase Morgan, a co-first author of the paper.

Why Viruses are Not So selfish After All

• The DNA segments, known as selfish genetic elements of viruses or bacteriophages (phages) were believed to exist solely to reproduce and spread themselves, offering no apparent benefit to their host organisms.
• Scientists saw them as genetic hitchhikers, inconsequentially passed down through generations.
• The selfish genetic elements known as “mobile introns” give their virus hosts a competitive edge against other viruses: phages have weaponized mobile introns to disrupt the reproduction of competing phages.

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Significance of This Discovery

• The selfish genetic elements are not always purely ‘selfish’ has broad implications for understanding genome evolution across all kingdoms of life.”
• The study’s results are crucial as phage viruses are increasingly used as therapeutic tools against antibiotic-resistant bacteria.
• Doctors have been using “cocktails” of phages to combat infections in this growing crisis, and the new information will likely be significant when multiple phages are deployed.
• Understanding that some phages use selfish genetic elements as weapons against others could help researchers understand why certain phage combinations may not achieve their full therapeutic potential.
• “The phages in this study can be used to treat patients with bacterial infections associated with cystic fibrosis,” said Biological Sciences Professor Joe Pogliano.

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