Genome, Proteome and Structure of a T7-Like Bacteriophage of the Kiwifruit Canker Phytopathogen Pseudomonas syringae pv. actinidiae

Pseudomonas syringae pv. actinidiae is an economically significant pathogen responsible for severe bacterial canker of kiwifruit (Actinidia sp.). Bacteriophages infecting this phytopathogen have potential as biocontrol agents as part of an integrated approach to the management of bacterial canker, and for use as molecular tools to study this bacterium. A variety of bacteriophages were previously isolated that infect P. syringae pv. actinidiae, and their basic properties were characterized to provide a framework for formulation of these phages as biocontrol agents. Here, we have examined in more detail phi Psa17, a phage with the capacity to infect a broad range of P.syringae pv. actinidiae strains and the only member of the Podoviridae in this collection. Particle morphology was visualized using cryo-electron microscopy, the genome was sequenced, and its structural proteins were analysed using shotgun proteomics. These studies demonstrated that phi Psa17 has a 40,525 bp genome, is a member of the T7likevirus genus and is closely related to the pseudomonad phages phi PSA2 and gh-1. Eleven structural proteins (one scaffolding) were detected by proteomics and phi Psa17 has a capsid of approximately 60 nm in diameter. No genes indicative of a lysogenic lifecycle were identified, suggesting the phage is obligately lytic. These features indicate that phi Psa17 may be suitable for formulation as a biocontrol agent of P.syringae pv. actinidiae.