Classification of Myoviridae bacteriophages using protein sequence similarity

Background: We advocate unifying classical and genomic classification of bacteriophages by integration of proteomic data and physicochemical parameters. Our previous application of this approach to the entirely sequenced members of the Podoviridae fully supported the current phage classification of the International Committee on Taxonomy of Viruses (ICTV). It appears that horizontal gene transfer generally does not totally obliterate evolutionary relationships between phages. Results: CoreGenes/CoreExtractor proteome comparison techniques applied to 102 Myoviridae suggest the establishment of three subfamilies (Peduovirinae, Teequatrovirinae, the Spounavirinae) and eight new independent genera (Bcep781, BcepMu, FelixO1, HAP1, Bzx1, PB1, phiCD119, and phiKZ-like viruses). The Peduovirinae subfamily, derived from the P2-related phages, is composed of two distinct genera: the P2-like viruses, and the HP1-like viruses. At present, the more complex Teequatrovirinae subfamily has two genera, the T4-like and KVP40-like viruses. In the genus T4-like viruses proper, four groups sharing >70% proteins are distinguished: T4-type, 44RR-type, RB43-type, and RB49-type viruses. The Spounavirinae contain the SPO1- and Twort-like viruses. Conclusion: The hierarchical clustering of these groupings provide biologically significant subdivisions, which are consistent with our previous analysis of the Podoviridae.