Genome of Xanthomonas oryzae bacteriophage Xp10: an odd T-odd phage

Xp10 is a lytic bacteriophage of the phytopathogenic bacterium Xanthomonas oryzae. Though morphologically Xp10 belongs to the Syphoviridae family, it encodes its own single-subunit RNA polymerase characteristic of T7-like phages of the Podoviridae family. Here, we report the determination and analysis of the 44,373 bp sequence of the Xp10 genome. The genome is a linear, double-stranded DNA molecule with 3' cohesive overhangs and no terminal repeats or redundancies. Half of the Xp10 genome contains genes coding for structural proteins and host lysis functions in an arrangement typical for temperate dairy phages that are related to the Escherichia coli lambda phage. The other half of the Xp10 genome contains genes coding for factors of host gene expression shut-off, enzymes of viral genome replication and expression. The two groups of genes are transcribed divergently and separated by a regulatory region, which contains divergent promoters recognized by the host RNA polymerase. Xp10 has apparently arisen through a recombination between genomes of widely different phages. Further evidence of extensive gene flux in the evolution of Xp10 includes a high fraction (10%) of genes derived from an HNH-family endonuclease, and a DNA-dependent DNA polymerase that is closer to a homolog from Leishmania than to DNA polymerases from other phages or bacteria.