P9, a temperate bacteriophage of Streptococcus equi

The genome sequence of Streptococcus equi subspecies equi (S. equi)(www.sanger.ac.uk) contains partial phage sequences which may affect virulence, gene regulation and expression. The present study was undertaken to characterize P9, a temperate bacteriophage of S. equi [J.G. Spanier, J.F. Timoney, Bacteriophages of Streptococcus equi, J. Gen. Virol., 35: 369–375, 1977.] to gain insight into genes that contributed to formation of the more virulent clonal S. equi from its putative ancestor, Streptococcus equi subspecies zooepidemicus (S. zooepidemicus). P9 has morphology typical of Siphoviridae with an icosahedral head and a long tail. P9 shares close relationship with phages of S. pyogenes. The overall gene order is similar to that of known prophages of lactic acid bacteria. ORF analysis revealed the presence of virulence factors including mitogens, hyaluronidase and streptodornase. Similar bacteriophage may have played an important role in the formation of the clonal S. equi by introducing virulence factors into S. zooepidemicus and disrupting functions of genes involved in DNA recombination and repair.