title: Genomic characterization of bacteriophage ValSw3-3 infecting Vibrio alginolyticus, a new member of a proposed genus in the family Siphoviridae

ling.chen (TALK)

institution: Shenzhen Institutes of Advance Technology, Chinese Academy of Science


V. alginolyticus is one of the most important opportunistic pathogen known to cause severe vibriosis in aquatic and marine animals worldwide. As an alternative approach to antibiotics treatment, phage therapy used to control pathogens has reemerged. In this work, a novel lytic Vibrio phage ValSw3-3 that efficiently infects virulent strains of V. alginolyticus was isolated from sewage water and characterized. Features obtained using transmission electron microscopy indicated ValSw3-3 is a siphovirus. This is the first report of V. alginolyticus lytic phage belonging to the Siphoviridae family. Genome sequencing and bioinformatics analysis were carried out and revealed that ValSw3-3 has a 39,846 bp double-stranded DNA with GC content of 43.1%, 97 promoters distributed in 11 promoter regions with a lower density (1.45 per ORF), and 44 predicted transcription terminators. The novelty of the phage indicated by in silico analysis is that we observed extremely low DNA (< 24%) and protein (<35%) homology to those of other phages deposited in GenBank. Additionally, ValSw3-3 has 69 open reading frames, 38 (55.1%) of which have homologous counterparts in NCBI nr database. Phylogenetic analysis based on large subunit terminases revealed that phage ValSw3-3 was grouped with the reported Vibrio phage jenny 12G5 (HQ632860.1) and Listonella phage phiHSIC (NC_006953.1), forming a distant clade that stands apart from the known genera ratified by ICTV, in line with the result of proteomic comparison of the phages. These observations warrant to propose a new viral genus containing ValSw3-3 within the family Siphoviridae. No lysogenic-cycle-related genes and known virulent genes were identified on the genome of ValSw3-3 and ValSw3-3 is able to infect the members of V. alginolyticus with high specificity, making it suitable for potential applications in controlling bacterial infections.