A Ralstonia solanacearum phage ϕRP15 is closely related to Viunalikeviruses and encodes 19 tRNA-related sequences

A T4-related phage infecting Ralstonia solanacearum was isolated in Thailand (ϕRP15). ϕRP15 virions showed unique morphology with star-like protrusions attached to the base plate via a stalk. The 168kb genome sequence of ϕRP15 was determined and found to encode 17 tRNAs (plus two tRNA pseudogenes). Ten of these phage-encoded tRNAs corresponded to codons that are relatively abundant in the phage but rare in the host, while others matched to codons frequent in both phage and host. Phylogenetic and proteomic analyses demonstrate that ϕRP15 forms a clade with Delftia phage ϕW-14, which in turn is placed as a sister group of viunalikeviruses. The hosts of ϕRP15 and ϕW-14 (R. solanacearum and Delftia acidovorans, respectively) belong to Betaproteobacteria, while most of the hosts of viunalikeviruses are of the Enterobacteriaceae belonging to Gammaproteobacteria. These phages may have evolved closely associated with their hosts that have very different life-styles in the natural habitats.