Genomic Characterization of Two Lytic Aeromonas veronii-Specific Bacteriophages Supports Their Potential as Safe Candidates for Phage Therapy in Aquaculture

Aeromonas veronii is an important bacterial pathogen responsible for motile Aeromonas septicemia (MAS) in aquaculture and is commonly controlled through antibiotic use. The increasing prevalence of antimicrobial resistance (AMR) has driven the need for alternative control strategies, among which bacteriophages have emerged as promising biocontrol agents. Here, we characterized two lytic A. veronii- specific bacteriophages, DJ6712 and FW6709, previously isolated from wastewater and aquaculture environments. Whole-genome sequencing and comparative genomic analyses were performed to investigate their genomic features, evolutionary relationships, and suitability for therapeutic applications. DJ6712 and FW6709 possess double-stranded DNA genomes of approximately 60 – 62 kb, each with a GC content of 62%. Genome annotation revealed genes associated with phage structure, DNA metabolism, and host lysis, including endolysin and Rz-like spanin proteins. Importantly, no antibiotic resistance genes, virulence factors, or lysogeny-related elements were detected. Phylogenetic analysis based on the conserved terminase large subunit (TerL) indicated that DJ6712 is most closely related to Aeromonas phage vB_C4, whereas FW6709 shows the closest evolutionary relationship to Aeromonas phage pAEv1. Whole-genome similarity analyses using VIRIDIC and Mash further demonstrated that DJ6712 and FW6709 are closely related to Aeromonas phage vB_C4 and Aeromonas phage BUCT551, respectively, within the family Casjensviridae . However, intergenomic similarity values below the commonly accepted species demarcation threshold (95%) support that DJ6712 and FW6709 represent genetically distinct A. veronii phage isolates within established phage lineages. Overall, these results expand the limited genomic knowledge of A. veronii -specific bacteriophages and support further investigation of DJ6712 and FW6709 for potential phage-based control of MAS in aquaculture.