Characterization and genomic analysis of a jumbo Aeromonas hydrophila phage BMBAH1, representing a candidate novel viral genus.

Aeromonas hydrophila is an opportunistic pathogen of fish, humans, and livestock, and has a severe negative impact on aquaculture development. Phage therapy is considered an alternative strategy for controlling bacterial infections and contamination. In this study, a novel phage, Aeromonas hydrophila BMBAH1, was isolated. Transmission electron microscopy showed that phage BMBAH1 had a long tail and an icosahedral head. Biological characterization indicated that phage BMBAH1 remained highly active across a broad range of temperatures and pH values, exhibiting long-term and significant inhibitory effects on host bacteria at an optimal multiplicity of infection (MOI) of 0.1. The genome of phage BMBAH1 is 237 kb in length with a guanine-cytosine (GC) content of 44.3%, and it was identified as a typical jumbo phage and predicted to contain 241 open reading frames (ORFs). Whole-proteome-based phylogenetic analysis, gene-sharing network analysis, and core protein clustering consistently indicated that phage BMBAH1 belongs to the family Chimalliviridae. However, phage BMBAH1 exhibited low intergenomic similarity to previously isolated phages, with values of approximately 30%. These results support the designation of phage BMBAH1 as the representative member of a candidate novel viral genus, designated Southlakevirus. Our findings expand the diversity of A. hydrophila phages and provide a promising genetic resource for further exploring biological characteristics of jumbo phages and developing biocontrol strategies.