Diversity and Lytic Potential of Novel Phages Targeting Xylella fastidiosa subsp. fastidiosa

Xylella fastidiosa is a xylem-limited plant-pathogenic bacterium responsible for several economically significant plant diseases, including Pierce's disease in grapevine. Current control strategies face significant challenges in completely eradicating this pathogen. As such, phage-based biocontrol has gained increasing interest as a biocontrol tool in crop management. In this study, we expand current knowledge on X. fastidiosa phage diversity by reporting the isolation and characterization of 35 novel phages (ViSe_1 to ViSe_35) capable of infecting European X. fastidiosa subsp. fastidiosa strains. These phages were isolated from sewage samples using a collection of Xanthomonas spp. and X. fastidiosa strains as primary hosts. Phylogenetic analysis revealed a substantial genomic diversity, with phages being taxonomically classified in five distinct families: Schitoviridae, Mesyanzhinovviridae, Casjensviridae, Autographiviridae, and Tectiviridae. Genomic analysis supports the proposal of four novel new genera and nine new species. Both highly specific and polyvalent phages were recovered, mostly depending on the isolation technique. All phages were able to infect strains from X. fastidiosa subsp. fastidiosa ST1, with 15 of them consistently and completely inhibiting bacterial growth. Notably, none of the phages harbored genes associated with lysogeny, virulence, or antibiotic resistance, suggesting a lytic life cycle and reinforcing their potential as biocontrol agents.