Genomic insights into Erwinia amylovora prophages: Diversity, defense strategies, and phage-host coevolution

Erwinia amylovora, the causative agent of fire blight in Rosaceae plants like apple and pear, is a major agricultural pathogen responsible for significant economic losses. This gram-negative phytopathogen has the potential to acquire antibiotic resistance and virulence genes, a situation that becomes more severe and restricts treatment options. Using an in silico approach, we analyzed 268 E. amylovora genomes and identified seven high-quality temperate prophages, all classified under Caudoviricetes, with average genome sizes of 44.2 kbp and 51 % GC content. These prophages exhibited unique genomic features, including tRNA genes (Ph-Ea644), anti-defense systems like ardc (Ph-Ea6-96), and regulatory/lysis genes (Ph-EaFC01). Comparative genomics and phylogenetic analyses grouped them into five clades, with Ph-Ea4-96, Ph-Ea3-97, and Ph-Ea2-97 being genetically identical. Functional annotation revealed streptomycin resistance genes and a CAZyme (GH23) in Ph-Ea7-3, virulence factors (e.g., alginate biosynthesis proteins), and six auxiliary metabolic genes (AMGs) linked to metabolic adaptation. Additionally, Ph-Ea644 encoded a cell wall-binding receptor protein. The prophages also carried defense systems (Gabija, CBASS) and 31 anti-CRISPR proteins (ACRs), suggesting evasion of host immunity. CRISPR-Cas analysis indicated fewer arrays and spacers in prophage-containing strains, underscoring CRISPR's role in lysogeny resistance. These findings highlight the genomic plasticity of E. amylovora prophages, their interactions with bacterial defenses, and their potential influence on pathogen evolution. This study enhances understanding of temperate phages in agricultural pathogens and underscores challenges in phage-based biocontrol strategies.