Phages communicate across species to shape microbial ecosystems.

Arbitrium is a communication system that helps bacteriophages to decide between lysis and lysogeny through secreted peptides. In this system, the arbitrium communication peptide (AimP) binds its cognate arbitrium receptor (AimR) to repress aimX (a negative regulator of lysogeny) expression, promoting lysogeny. It has been assumed that each AimR responds exclusively to its own AimP. Here, we challenge this view by demonstrating cross-communication between arbitrium systems. Using prototypical arbitrium phages, we show that AimP peptides can bind and repress non-cognate AimR receptors, promoting lysogeny and reducing prophage induction. Structural and biochemical analyses reveal conserved receptor features that permit cross-recognition of non-cognate peptides while preserving recognition of cognate partners. In mixed lysogenic cultures, these interactions alter induction outcomes, underscoring their ecological significance. Extending to infection contexts, we demonstrate that crosstalk favors lysogeny of incoming phages in cells harboring compatible systems. These findings establish that phages engage in cross-species communication via peptide signaling, reshaping microbial communities in unexpected ways.