A study of the novel Aeromonas veronii bacteriophage AerV_348 reveals an unclassified group of aquatic phages within the class Caudoviricetes.

Aeromonas veronii is a mesophilic bacterium that is widely distributed in terrestrial and aquatic environments and is able to cause disease in various species of fish and other animals. In humans, pathogenic A. veronii causes mainly foodborne infections due to increased consumption of chilled seafood. In this study, the novel lytic Aeromonas veronii phage AerV_348 was isolated and characterized. The phage and its bacterial host, A. veronii CEMTC 9558, were isolated from Lake Pestroe, North Kazakhstan. AerV_348 is a dsDNA virus with a genome size of 43,779 bp. The phage is lytic and has a very narrow host range, reproducing only in its host strain. The latent time was determined to be 50 minutes, and the burst size was 55 plaque-forming units per cell. The AerV_348 genome content corresponds to a lytic phage with myovirus morphology that does not contain genetic signs of being a temperate phage. Comparative analysis revealed that AerV_348 belongs to a large group of unclassified tailed phages that infect aquatic bacteria such as Vibrio, Shewanella, and Oceanospirillum. All of these phages have similar genome sizes and structures and share a conserved cluster of genes that encode structural proteins. However, these phages demonstrate high variability in a cluster of genes responsible for DNA metabolism and translation. Currently, the classification of this phage group is not clear, and new phage genomic data may help to separate this group as a new taxonomic unit within the class Caudoviricetes.