Bacteriophages, viruses infecting bacteria, have a strong influence on bacterial community structures and ecosystem functioning in the ocean. Only little is known so far about roseophages, those infecting the important and widespread Roseobacteraceae family. Here, roseophage diversity in the North Sea was investigated by isolation, cultivation and whole genome sequencing. More than 100 new roseophages infecting the ecologically relevant genera Sulfitobacter, Lentibacter, and Octadecabacter have been isolated and genome sequenced, revealing an impressive diversity. The new phages vary in genome size, morphology and lifestyle and could be assigned to eight families in the class Caudoviricetes, comprising four already existing and four newly proposed families. The majority of the new isolates belonged to one large group of highly similar, potentially species-level related Sulfitobacter phages. Host range determination against their original isolation host strains revealed a complex infectivity network. Genome analysis of these phages and of thirty whole-genome sequenced host strains revealed a high degree of microdiversity on both sides
