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 potential 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 icosa-hedral head (56.50 ± 4.19 nm in diameter) and a long tail (143.03 ± 5.32 nm in length), ex-hibiting a typical siphovirus-like morphology within the class Caudoviricetes. The phage demonstrated wide stability across various temperatures, pH levels, and salinities. Genomic sequencing showed that vB_ValS-L9 has a circular double-stranded DNA genome of 43,884 bp with a G+C content of 43.55% 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 pro-vides substantial prophylactic and therapeutic protection against V. alginolyticus L4 infec-tion, 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.