New study helps improve the understanding of bacteria and viruses

A new study has found that existing CRISPR anti-viral immunity is often a disadvantage to bacterium when infected by certain viruses.

The study was carried out by researchers at the University of Exeter, UK, with support from the University of Montpellier, France, and the University of Otago, New Zealand.

CRISPR has become well known for its repurposing as a tool for precise genetic engineering. However, CRISPR systems (segments of DNA) naturally occur in many bacteria and provide bacteria with immunity against viruses or foreign DNA.

Otago researchers Dr Chris Brown, Dr Teyuan Chyou and Professor Peter Fineran, questioned whether autominnunity is important in other bacterial pathogens and analysed over 170,000 bacterial genomes, including diverse pathogens.

“We searched the DNA sequence for CRISPR systems and integrated viral genomes. We found that CRISPR autoimmunity was likely to be widespread in nature,” Dr Brown said.

Professor Fineran explained this suggested that triggering the powerful CRISPR defence systems is risky for a bacterium: “Importantly, this may help answer a long-standing question of why these defence systems are absent in 60 percent of bacteria.”

For example, the researchers said, Staphylococcus aureus pathogens that often take up extra genes to become multidrug-resistant, seldom have CRISPR defence. An example of this is MRSA (Methicillin-resistant Staphylococcus aureus) an infection often occurring in people who have been in hospitals or other healthcare settings, which has become resistant to many of the antibiotics used to treat ordinary staph infections. It seldom has CRISPR defence.

This study forms part of larger studies aimed at understanding the arms race between bacteria and their viruses and has significant implications.

“Importantly, this change in understanding of pathogen defence systems will inform the design of new treatments, particularly those using viruses that kill pathogenic or antibiotic-resistant bacteria,” Dr Brown explained.

The study was published in Nature.