These relationships carry evolutionary relevance, since our proteomic analyses, combined with the phylogenetic studies [100], suggest that the Myoviridae are mainly influenced by AC220 concentration vertical evolution rather than by horizontal gene transfer. As observed in BIX 1294 the Cluster dendrogram, the clusters are populated unevenly – several include only one phage while two, the largest, include dozens phages. This reflects the fact that past phage research has focused on coliphages, and suggests that

we should broaden our research to include phages from a broader range of bacteria. Table 4 Concordance of classifications Classification ICTV Proteomic Tree 2 —- Phage_Finder This work Reference ICTV VIIIth Report, 2005 Edwards and Rohwer, 2005 Serwer et al., 2004 Fouts, 2006  

Approach Traditional Signature genes Large terminase   CoreGenes Phage or phage group T4, Aeh1, KVP40, RB43, RB49, 25, 31 44RR2.8t, 65 T4 T4, KVP40, RB49   T4, Aeh1, KVP40, RB43, RB49, 25, 31 44RR2.8t, FHPI ic50 65   P1     P1 P1   P2, Fels-2, HP1, HP2, K139, φCTX, 186 P2. HP1, HP2, φCTX P2, Fels-2, HP1, HP2, L413-C, 186; Mu P2, φCTX, 186 (HP1 occupies a separate position) P2, Fels-2, HP1, HP2, K139, L-413C, φCTX, 186   Mu Mu     Mu   SPO1 K   P100, Twort SPOl, K, P100, Twort   ΦH         Comparison of our results with those of the ICTV (ICTV VIIIth Report, 2005), Proteomic Tree 2 (Edwards and Rohwer, 2005), Phage_Finder (Fouts, 2006) and phylogeny of terminases (Serwer et al., 2004). Among the 102 analyzed Myoviridae, phage Mu displayed the most significant evidence of horizontal gene exchange. This Tolmetin virus is related to three members of pilus-specific Siphoviridae infecting Pseudomonas aeruginosa (DMS3, D3112, B3 [59, 60, 101]), sharing 20 to 40% of its genes with each of them. These phages can be viewed as true hybrids, produced by recombination of different ancestors and, like the couple lambda/P22 (to be described in a future paper), cross family boundaries based on tail morphology. Nonetheless, the majority of Myoviridae, when forced to

cluster, do so in a logical manner: upgrading of the ICTV genus “”P2 phages”" to the Pduovirinae with two genera (“”P2 viruses”" and “”HP1 viruses”") is a straightforward proposal and the same is true for the Spounavirinae (SPO1 viruses and Twort viruses). Relationships among T4-like phages are more complicated. We reject the postulated inclusion of the cyanophages since their overall similarity to T4 is too low for consideration, at least according to our criteria. Comeau and Krisch [29] have recently recognized three groups of T4-related phages. The “”Near T4″” group containing the T-evens, Pseudo T-evens, and Schizo T-evens; the “”Far T4″” clade including Exo-T4 phage RM378; and, the “”Cyano T4″” assemblage. We believe that the latter are sufficiently different from the other T4 viruses to be excluded from the Teequatrovirinae at this time.