Phage-encoded PciP differentially regulates Pseudomonas aeruginosa swarming motility and quorum-sensing-associated phenotypes via CheV-dependent and CheV-independent mechanisms

ABSTRACT Pseudomonas aeruginosa is an opportunistic pathogen whose intrinsic antibiotic resistance and complex virulence regulatory networks pose major clinical challenges. Bacteriophages and their encoded proteins have emerged as potential modulators of bacterial physiology, yet the mechanisms by which phage proteins influence bacterial virulence remain poorly understood. In this study, we identified PciP, an early protein encoded by the lytic phage PAYQ66, which suppresses pyocyanin production and swarming motility in P. aeruginosa . PciP reduces PQS levels and suppresses quorum-sensing gene transcription. PciP associates with CheV, and genetic analysis indicates that CheV is required for the PciP-mediated inhibition of swarming but not for the PciP-mediated suppression of PQS and pyocyanin production. Expression of PciP attenuates virulence in infection models. Together, these findings reveal that PciP differentially modulates swarming motility and quorum-sensing-associated phenotypes via CheV-dependent and CheV-independent mechanisms. These results provide mechanistic insights into how a phage-encoded protein reprograms host regulatory networks. IMPORTANCE Pseudomonas aeruginosa is a major opportunistic pathogen that is increasingly difficult to treat due to intrinsic and acquired antibiotic resistance. Bacteriophages encode diverse proteins that can interfere with bacterial regulatory networks, yet many remain functionally uncharacterized. Here, we characterize PciP, a protein encoded by the lytic phage PAYQ66, and show that it modulates bacterial motility and quorum-sensing-associated phenotypes through distinct mechanisms. PciP associates with CheV and inhibits swarming motility in a CheV-dependent manner, whereas PciP-mediated suppression of PQS and pyocyanin production persists in the absence of CheV. These combined effects significantly reduce pathogenicity in both animal and plant infection models. This study advances our understanding of phage-host interactions by demonstrating that a phage-encoded protein can differentially modulate host regulatory outputs via CheV-dependent and CheV-independent mechanisms.