Identification and Genomic Analysis of a New Viral Species With Low Similarity to Existing Viruses

Viruses are among the most abundant and diverse biological entities on Earth. Over the past decades, metagenomic sequencing has revealed thousands of viral genomes. However, viral isolation methods remain indispensable for discovering viruses that are missed by metagenomic sequencing due to limitations like low abundance (1, 2). Here, a novel phage, vB_PshM_Y4, which infects Pseudoalteromonas shioyasakiensis, an economically important, opportunistic marine pathogen was isolated. A comparison of vB_PshM_Y4 with over 15 million viral genomes, including both cultivated and uncultivated viruses in the NCBI and IMG/VR v4 datasets, found no closely related genome. This study provides evidence that traditional isolation methods can detect viruses that cannot be identified through metagenomic sequencing. In addition, a comparison of virus isolates deposited in the NCBI database with uncultured viruses in the IMG/VR viral database shows that approximately only half of the isolates can be detected using metagenomic approaches. Notably, viruses that are not able to be detected by metagenomic sequencing often exhibit low abundance and possess unique genomes. These results suggest that traditional viral isolation methods remain important for obtaining rare, low-abundance viruses and underscore the significance of traditional experimental methods in the era of metagenomes.