Characterization and Genome Analysis of a Novel Vibrio Alginolyticus Phage and Its Biocontrol Efficacy in Pearl Oyster Aquaculture

A novel lytic bacteriophage, designated vB_ValS-L9, infecting the potentially pathogenic bacterium Vibrio alginolyticus L4, was isolated from a coastal aquaculture area in Beihai, China. Transmission electron microscopy revealed that vB_ValS-L9 possesses an icosahedral head (56.50 ± 4.19 nm in diameter) and a long tail (143.03 ± 5.32 nm in length), exhibiting a typical siphovirus-like morphology within the class Caudoviricetes. The phage demonstrated stability across various temperatures, pH levels, and salinities. Genomic sequencing showed that vB_ValS-L9 has a circular double-stranded DNA genome of 44,025 bp with a G + C content of 43.56% and 61 predicted ORFs. No tRNA, virulence, or antibiotic resistance genes were identified. Genomic and phylogenetic analyses, including ANI, VICTOR, VIRIDIC, and conserved protein phylogenies, identified vB_ValS-L9 as a novel species that, together with Vibrio phages Artemius and VapS30, forms a new genus in the class Caudoviricetes, for which the name Artemiovirus is proposed. Furthermore, in vivo trials using juvenile pearl oysters (Pinctada martensii) revealed that vB_ValS-L9 provides substantial prophylactic and therapeutic protection against V. alginolyticus L4 infection, especially when the phage was administered before bacterial challenge. Collectively, these findings suggest that vB_ValS-L9 shows potential as a safe, environmentally robust, and promising biocontrol candidate for managing vibriosis in aquaculture.