Lysogenic Conversion of the Phytopathogen Ralstonia solanacearum by the P2virus φRSY1

A P2-like phage phi RSY1 infecting the phytopathogen Ralstonia solanacearum was isolated and characterized. The 40-kb genome of phi RSY1 showed high sequence similarity to the Ralstonia phage phi RSA1 and the GMI1000 prophage phi RSX. The major genomic differences between these phages were the different orientation of the int gene and the gene content close to the cosL. phi RSY1 and phi RSX use a 15-base 3 0 portion of the serine tRNA(GGA) gene as attB, while phi RSA1 uses a 45-base 3 0 portion of the arginine tRNA(CCG) gene. The different orientation of int in the genomes means that the gene arrangements in the prophage states are reversed in phi RSY1 and phi RSA1. Several putative gene products of phi RSY1 may affect the bacterium's fitness. phi RSY1 contains an open reading frame (ORF) that seems to encode a protein similar to Vgr in the type VI secretion system of various bacterial species. phi RSY1 lysogens showed phenotypic changes including enhanced twitching motility, large colony formation, and easy aggregation of cells, suggesting involvement of this ORF in the changes. In view of these phage gene arrangements, we surveyed prophages in the genomes of various R. solanacearum strains and found that the P2-like phages of R. solanacearum (14 phages) consist of two major groups: the phi RSY1-type and the phi RSA1-type. The relationships and evolution of these P2-like phages inferred from our data are discussed in detail.