Bacteria protect themselves against bacteriophage (phage) infection using defensive systems, with phages co-evolving counter-resistant strategies. Several anti-phage systems have been identified and their modes of action determined. Additionally, nine novel systems were recently reported, and thus remain to be characterised. My proposed research builds upon this recent discovery and aims to dissect the molecular and structural details of the novel anti-phage system named Zorya. Two types of Zorya systems with distinct host range have been described, sharing two conserved components, ZorA and ZorB. These two proteins have been proposed to act through a conserved mechanism, based on formation of a putative ion-channel, to neutralise phage infection. I am to test this hypothesis with the following aims: - To probe the organisation and function of Zorya II in vivo - To define the mechanism by which Zorya II protects from phage infection - To identify the trigger of Zorya II anti-phage activity Elucidating the molecular basis of interactions between bacteria and their viral predators and characterising the molecular mechanism of anti-phage systems is vital to understand the nature of bacteria-phage co-evolution and its capacity to shape the composition and dynamics of polymicrobial environments, with implication for therapeutic and biotechnological applications. Bacteriophages (phages) are small, non-living entities that depend on their bacterial host for survival.Bacteria and phages are involved in cycles of co-evolution, where bacteria develop mechanisms to prevent infection from their predators and phages adapt to overcome these new strategies. Of recent discovery is a novel anti-phage system, named Zorya. It has been observed that bacterial strains that carry a Zorya system, when infected by a phage, can initiate early cell death to avoid its replication. Nevertheless, little is known about the exact mechanism through which the system is activated and can cause growth cessation, to arrest the phage infection. I will explore the mechanism by which the Zorya system leads to bacterial death, addressing how the single components of the Zorya system can assemble to bring about the death of infected host bacteria and which components of the phage invader is fundamental to determine the initiation of this pathway.