A phage communication peptide alters Bacillus subtilis colony development and promotes sporulation

Temperate Bacillus phages use arbitrium peptides to coordinate lysis-lysogeny decisions, but whether the mature communication peptide can be sensed directly by Bacillus subtilis and affect its physiology and behavior is unknown. Here we show that the {varphi}3T arbitrium peptide SAIRGA elicits a sequence- and stereochemistry-dependent response in Bacillus subtilis that is strongly expressed in surface-grown colony biofilms but is not accompanied by comparable changes in planktonic growth or static-liquid pellicle morphology. The response persists in the absence of AimR, the canonical arbitrium receptor. Within colonies, SAIRGA alters spatial PtapA activity and increases heat-resistant spore formation without increasing total viable cell yield. Untargeted metabolomics reveals broad dose-dependent remodeling that tracks peptide activity, while program-level proteomics independently converges on late-sporulation and mature-spore-associated states. This study highlights how a phage-derived peptide may act as a signal, enabling the host to pivot toward a survival-focused developmental state.