Isolation and characterization of Avs-1, a bacteriophage effective against the aquaculture pathogen Aeromonas veronii

Aeromonas veronii is a representative pathogen resulting in significant economic losses in aquaculture. As a potential antibacterial agent, bacteriophage has attracted wide attention. Herein, a virulent phage named Avs-1 that infects Aeromonas veronii was isolated from sewage. Avs-1 demonstrated an optimal multiplicity of infection (MOI) of 0.1, with a 20-min latent period and a 130-min burst period. Cryo-electron microscopy structural analysis revealed that Avs-1 possesses an icosahedral capsid composed of 415 copies of the major capsid protein arranged in a T = 7 lattice, along with a long non-contractile tail typical of the Siphoviridae family. Phage resistance in strain AV0110 was linked to a frameshift mutation in the manB gene encoding phosphomannomutase (PMM). The genome of phage Avs-1 consists of 44,364 bp double-stranded circular DNA, in which the endolysin (Lys40) has a modular structure with a N-acetylmuramidase domain at N-terminus and a peptidoglycan (PG)-binding domain at C-terminus. Notably, endogenous expression of Lys40 could greatly inhibit the growth of E. coli but could not lyse them. Avs-1 exhibited significant antibacterial effect in vitro and increased tilapia survival rate by 50% when used in vivo. This study provides a theoretical basis for further research on the interaction between pathogens and phages, and the prevention and treatment of Aeromonas veronii and highlights the potential of Avs-1 as a targeted biocontrol agent against Aeromonas veronii infections in aquaculture.IMPORTANCEIn this study, we present an eco-friendly approach to address a critical issue in aquaculture: Aeromonas veronii infections, which cause significant economic losses. We turned to nature's bacterial predators-bacteriophages and viruses that specifically infect and kill bacteria. From sewage samples, we isolated a novel phage named Avs-1, which effectively targets A. veronii. Genomic and structural analyses were conducted to elucidate its mechanisms. Notably, we also identified a key gene that enabled bacteria to resist phage adsorption, which provides critical insights for future phage applications. Most importantly, in our laboratory tests, the Avs-1 bacteriophage demonstrated potent antibacterial activity and increased the survival rate of tilapia infected with A. veronii by 50%. The potential of Avs-1 bacteriophage as a targeted, environmentally friendly "biological pesticide" for controlling infections in aquaculture offers a promising alternative to conventional antibiotics.