Isolation and genomic characterization of Shewanella phage vB_SheP_NIOT1 reveals a candidate novel genus within Queuovirinae

The marine ecosystem harbors numerous opportunistic bacteria, among which Shewanella spp . has gained increasing attention due to its medical significance. The extensive use of antibiotics has led to the emergence of antibiotic-resistant bacteria; therefore, bacteriophages are being considered effective alternative therapeutic agents, although they remain poorly characterized. In this study, we isolated and broadly characterized a lytic bacteriophage, designated vB_SheP_NIOT1, against Shewanella spp . from seawater. The phage exhibited a non-enveloped icosahedral capsid with a long, flexible, non-contractile tail, with an approximate length of 210 nm. It displayed strong environmental tolerance and stable infectivity. The latent period was approximately 60 min, and the burst size was approximately 120 PFU per infected cell. Genomic characterization revealed that vB_SheP_NIOT1 has a 62 kb circular dsDNA genome with 49% GC content and encodes 107 predicted coding sequences, with no antimicrobial resistance genes, virulence factors, tRNAs, or mobile genetic elements. Comparative genomic analysis revealed a highly divergent nucleotide sequence and conserved proteomic genes. Taxonomic analysis using VIRIDIC, VICTOR, and vConTACT3 classified the phage into a candidate novel genus within Queuovirinae, rather than assigning it to any currently established genus.