Global Acetylome Profiling Reveals Extensive Lysine Acetylation in Acinetobacter baumannii Bacteriophage Proteins

Post-translational modifications (PTMs) are increasingly recognized as potential regulators of bacteriophage-host interactions, yet their functions remain largely undefined. Here, we present the first proteome-wide characterization of lysine acetylation in a bacteriophage, using Acinetobacter baumannii myovirus vB_AbaM_DLP3 as a model to investigate host-imposed modification during infection. An optimized proteomic workflow that eliminates chemical artifacts and improves peptide identification accuracy enabled detection of 86 acetylated proteins, representing nearly one-third of the DLP3 proteome. Comparative analysis of purified virions and infected host cells revealed distinct acetylation profiles, consistent with host-driven, transient modifications that are removed or lost after lysis. Functional annotation showed that acetylation predominantly targets proteins involved in DNA replication, genome packaging, and structural assembly. Structural modeling of the major capsid and replication-associated proteins demonstrated that acetylation neutralizes positive surface charges, potentially weakening DNA binding and intercapsomer interactions critical for replication and capsid cohesion. Together, these findings establish lysine acetylation as a widespread and dynamic feature of phage infection and identify host-imposed acetylation as a potential regulatory mechanism that modulates phage replication, assembly, and infectivity. This work expands the molecular framework of phage-host interactions, providing a foundation for future studies aimed at understanding how bacterial PTMs influence phage function and for engineering phages resistant to host-mediated inhibition. ImportanceBacteriophages are being developed as alternatives to antibiotics, yet little is known about how bacterial hosts chemically modify phage proteins during infection. This study reveals that A. baumannii imposes extensive lysine acetylation on its infecting phage DLP3, affecting proteins involved in DNA replication and structural assembly. By demonstrating that acetylation neutralizes positive surface charges and is largely absent after phage release, this work identifies host-driven acetylation as a previously unrecognized, reversible mechanism that may influence phage infectivity. Understanding how bacteria use post-translational modifications to interfere with phage function provides new insight into phage-host molecular interactions and informs strategies for engineering therapeutic phages resistant to host-imposed inhibition.