Isolation and characterization of the virulent phage Savoy targeting Xylella fastidiosa subsp. fastidiosa

Xylella fastidiosa is a xylem-limited, vector-borne bacterial pathogen that infects a wide range of plant species worldwide, causing severe diseases and substantial economic losses in key crops such as olives, grapes, plums, almonds, and citrus. With few resistant cultivars available, current management strategies rely heavily on chemical control of insect vectors. Here, we report the isolation and characterization of a virulent bacteriophage, Savoy, exhibiting strong lytic activity against the grapevine-infecting X. fastidiosa strain WM1. Transmission electron microscopy identified Savoy as a Siphophage with a long contractile tail. The phage displayed optimal infectivity at a multiplicity of infection of 1 and remained stable across broad temperature (4–45 °C) and pH (3–11) ranges. In vitro assays demonstrated that Savoy effectively lysed planktonic bacterial cells and inhibited biofilm formation. Genome analysis revealed a 61,990 bp genome organized into functional modules associated with DNA metabolism, head and packaging, tail structure, lysis, and connector proteins. No known virulence factors, antimicrobial resistance genes, or CRISPR elements were detected. Multiple genes in Pseudomonas soli Savoy-resistant mutants harbored single nucleotide polymorphisms affecting diverse functional proteins. These findings highlight phage Savoy as a promising candidate for the development of sustainable phage-based biocontrol strategies against X. fastidiosa, with potential to reduce reliance on chemical treatments and mitigate crop losses.