Researchers at University of Utah Health have uncovered a new way bacteria recognize viral invaders. The work, published in Science, shows that a protease enzyme produced by certain bacteriophages directly cleaves a sensor protein inside the bacterial cell. That cleavage acts as an alarm, triggering a defensive immune response called CBASS, which ultimately causes the infected bacterium to kill itself before the virus can spread.
This mechanism is distinct from other antiviral systems that detect viral genetic material. Instead, the trigger is the activity of a viral protein on a host protein—a finding the authors describe as unexpected. Because CBASS is one of the most common forms of bacterial immunity, understanding this detection step could help researchers engineer phages that evade or overcome bacterial defenses, improving phage therapy against antibiotic-resistant infections.
The study also has implications for human immunity. CBASS is related to an immune pathway found in people, suggesting the system has been conserved across billions of years of evolution. The authors note that bacteria offer a fast experimental system to probe immune questions, and the conservation hints at the pathway's fundamental importance in fighting viruses.