Phage Portal Proteins Suppress Bacterial Stringent Response to Promote Infection

Bacteria restrict viral replication not only through dedicated defense systems but also by entering global physiological states that limit cellular resources. How phages counter such host-imposed physiological barriers remains poorly understood. The stringent response (SR), mediated by the alarmones ppGpp and pppGpp, induces a growth-restrictive state that can act as a barrier to bacteriophage infection. Here we show that elevated alarmone levels delay T7-mediated host lysis, whereas (p)ppGpp-deficient cells are hypersensitive to infection, establishing alarmone signaling as a physiological constraint on phage replication. A systematic functional screen identifies the essential capsid portal protein Gp8 as a viral factor genetically linked to SR-dependent host physiology. Gp8 directly binds the alarmone synthetases RelA and SpoT, selectively inhibiting their synthetase activities in vitro and suppressing alarmone accumulation in vivo. Phages carrying interaction-defective portal mutations exhibit impaired replication, delayed lysis, and sustained (p)ppGpp elevation during infection, defects that are alleviated in SR-deficient hosts. Structural and mutational analyses reveal electrostatically mediated interfaces required for targeting RelA and SpoT. Portal proteins from diverse coliphages share similar structural features, interact with stringent-response enzymes, and display SR-linked phenotypes, indicating a broadly conserved viral strategy. Together, these findings identify phage portal proteins as a previously unrecognized class of viral counter-defense factors that target a central bacterial stress signaling pathway, revealing that essential structural virion components can moonlight as regulators of host stress physiology.