The arms race between bacteria and viruses

– Oct. 30, 2023

Bacteria also possess an immune system. They can be infected by small viruses known as bacteriophages. These viruses inject their DNA into the bacterium, after which the bacterium acts as a virus factory, producing new viral particles until the cell bursts.

Protection with the CRISPR-Cas System

To protect itself, the bacterium employs the CRISPR-Cas system. When the bacterium becomes infected, and the virus injects its DNA into the bacterium, the bacterium recognizes this as non-self and incorporates a small portion of the viral DNA into its own DNA. Consequently, the bacterium creates a database of viral DNA. These DNA fragments are used to recognize and dismantle this DNA when the bacterium is infected once more by the same type of bacteriophage. This is referred to as the CRISPR-Cas system.

Cunning viruses

Bacteriophages consistently devise ingenious methods to evade this system, enabling them to infect the cell. Researchers have now discovered a new way in which viruses can disable the CRISPR-Cas system. This research not only promises to expand our knowledge of the microbial world around us but also offers opportunities to enhance the safety of gene editing and develop more efficient alternatives to antibiotics.

Can't see the wood for the trees

Researchers have found that bacteriophages have modified their own genome. They have added repetitions of the CRISPR-Cas system to their DNA. The result is the production of significant quantities of so-called small non-coding RNA anti-CRISPRs, or Racrs, within the bacterium. With these Racrs, the CRISPR-Cas complex cannot form correctly, thus disabling the bacterium's immune response. Additionally, the bacterium's immune system is effectively blinded by the extensive quantity of Racrs, rendering it incapable of recognizing the bacteriophage because it is distracted by all the Racrs present within the cell.

New possibilities

For several years, people have been using the CRISPR-Cas mechanism to precisely modify DNA. To better master this mechanism, it is advantageous to keep an eye on the new strategies employed by bacteriophages. The Racrs can serve as a 'kill switch' for the process, which is incredibly useful for improved process control.

Furthermore, bacteriophages might potentially be utilised as an alternative to antibiotics in the future, targeting specific bacterial species. Racrs can also prove very useful for this purpose: if the bacterium causing the infection possesses a CRISPR-Cas system, the bacteriophage must possess the appropriate Racrs to bypass this system.


Autor: Noa Hudepol