Characterization and Genomic Analysis of ValSw3-3, a New Bacteriophage Infecting Vibrio alginolyticus.

A novel lytic bacteriophage, ValSw3-3, which efficiently infects pathogenic strains of , was isolated from sewage water and characterized by microbiological and genomic analyses. Transmission electron microscopy indicated that ValSw3-3 has the morphology of siphoviruses. This phage can infect four species in the genus and has a latent period of 15 min and a burst size of 95 ± 2 PFU/infected bacterium. Genome sequencing results show that ValSw3-3 has a 39,846-bp double-stranded DNA genome with a GC content of 43.1%. The similarity between the genome sequences of ValSw3-3 and those of other phages recorded in the GenBank database was below 50% (42%), suggesting that ValSw3-3 significantly differs from previously reported phages at the DNA level. Multiple genome comparisons and phylogenetic analysis based on the major capsid protein revealed that phage ValSw3-3 is grouped in a clade with five other phages, including phage phiHSIC (GenBank accession no. NC_006953.1), phage P23 (MK097141.1), phage pYD8-B (NC_021561.1), phage 2E1 (KX507045.1), and phage 12G5 (HQ632860.1), and is distinct from all known genera within the family that have been ratified by the International Committee on Taxonomy of Viruses (ICTV). An proteomic comparison of diverse phages from the family supported this clustering result and suggested that ValSw3-3, phiHSIC, P23, pYD8-B, 2E1, and 12G5 should be classified as a novel genus cluster of A subsequent analysis of core genes also revealed the common genes shared within this new cluster. Overall, these results provide a characterization of phage ValSw3-3 and support our proposal of a new viral genus within the family Phage therapy has been considered a potential alternative to antibiotic therapy in treating bacterial infections. For controlling the vibriosis-causing pathogen , well-documented phage candidates are still lacking. Here, we characterize a novel lytic phage, ValSw3-3, based on its morphology, host range and infectivity, growth characteristics, stability under various conditions, and genomic features. Our results show that ValSw3-3 could be a potent candidate for phage therapy to treat infections due to its stronger infectivity and better pH and thermal stability than those of previously reported phages. Moreover, genome sequence alignments, phylogenetic analysis, proteomic comparison, and core gene analysis all support that this novel phage, ValSw3-3, and five unclassified phages form a clade distant from those of other known genera ratified by the ICTV. Thus, we propose a new viral genus within the family to accommodate this clade, with ValSw3-3 as a representative member.