Isolation and Characterization of a Roseophage Representing a Novel Genus in the N4-like Rhodovirinae Subfamily Distributed in Estuarine Waters

Abstract Background Roseobacteraceae, often referred to as the marine roseobacter clade (MRC), are pivotal constituents of bacterial communities in coastal and pelagic marine environments. During the past two decades, 75 roseophages that infect various Roseobacteraceae lineages have been isolated. The N4-like Rhodovirinae subfamily, which encompasses 15 members, represents the largest clade among these roseophages. Results In this study, we isolated a novel roseophage, vB_DshP-R7L, that infects Dinoroseobacter shibae DFL12 from Xiamen Bay in the East China Sea. Conserved genes of Schitoviridae have been identified in the genome of vB_DshP-R7L, and following phylogenetic analysis suggest that the newly isolated phage is a member of the Rhodovirinae subfamily and is indicative of a newly proposed genus, Xianganvirus. The genome of vB_DshP-R7L harbors six auxiliary metabolic genes (AMGs), most of which potentially enhance DNA de novo synthesis. Additionally, a gene encoding ribosomal protein was identified. Comparative genomic analysis of AMG content among Rhodovirinae indicates a distinct evolutionary history characterized by independent ancient horizontal gene transfer events. Read-mapping analysis reveals the prevalence of vB_DshP-R7L and other Rhodovirinae roseophages in estuarine waters. Conclusions Our work illustrates the genomic features of a novel roseophage clade among N4-like Rhodovirinae. The AMG content of vB_DshP-R7L are under severe purification selection, which revealed their possible ecological importance. We also demonstrated that vB_DshP-R7L and other Rhodovirinae roseophages are restrictively distributed in estuaries. Our isolation and characterization of this novel phage expand the understanding of the phylogeny, gene transfer history and biogeography of N4-like Rhodovirinae infecting marine Roseobacteraceae.