Complete Genome Sequence of the Giant Virus OBP and Comparative Genome Analysis of the Diverse φKZ-Related Phages

The 283,757-bp double-stranded DNA genome of Pseudomonas fluorescens phage OBP shares a general genomic organization with Pseudomonas aeruginosa phage EL. Comparison of this genomic organization, assembled in syntenic genomic blocks interspersed with hyperplastic regions of the phi KZ-related phages, supports the proposed division in the EL-like viruses, and the phiKZ-like viruses within a larger subfamily. Identification of putative early transcription promoters scattered throughout the hyperplastic regions explains several features of the phi KZ-related genome organization (existence of genomic islands) and evolution (multi-inversion in hyperplastic regions). When hidden Markov modeling was used, typical conserved core genes could be identified, including the portal protein, the injection needle, and two polypeptides with respective similarity to the 3'-5' exonuclease domain and the polymerase domain of the T4 DNA polymerase. While the N-terminal domains of the tail fiber module and peptidoglycan-degrading proteins are conserved, the observation of C-terminal catalytic domains typical for the different genera supports the further subdivision of the phi KZ-related phages.