Scientists find bacteria use dormant phages for immunity

Bacteria face threats from viruses known as bacteriophages, or phages for short. Scientists have been investigating how these single-celled organisms defend themselves against these viral invaders. Understanding this process could improve our knowledge of human immunity and help in disease treatment. Researchers from Johns Hopkins Medicine have discovered that some bacteria, like Streptococcus pyogenes, gain immunity by capturing genetic material from dormant phages. During a phase when phages are not actively attacking, bacteria can take this genetic information and create a "memory" of the invader. This memory is passed down to future generations of bacteria, allowing them to recognize and fend off these phages. Their study, published on March 12 in the journal Cell Host & Microbe, provides insights into how harmful bacteria, including those that cause strep throat and serious infections, can become dangerous to humans. Joshua Modell, an associate professor at Johns Hopkins, noted that understanding how bacteria develop survival skills against new phage attacks is crucial. Bacteria have tools like the CRISPR-Cas system, which helps them recognize and destroy phage DNA from past infections. The researchers found that this system is more effective when working with dormant phages, which allows bacteria to gather information without the immediate threat of infection. In the study, scientists infected bacterial populations with both dormant and non-dormant phages. They found that the CRISPR system worked best with the dormant ones, leading to a successful genetic memory creation. By analyzing surviving bacteria, the team mapped out new DNA memories associated with immunity. The researchers believe their findings are similar to how vaccines work with weakened viruses. The ongoing research will explore how these systems function against non-dormant phages, which pose different challenges. Modell emphasized that understanding these defenses could lead to new phage therapies, especially for infections resistant to antibiotics. The study was supported by various institutions, including the National Institutes of Health and the National Science Foundation.