Genomic Characterization of the Filamentous Integrative Bacteriophages φRSS1 and φRSM1, Which Infect Ralstonia solanacearum

The genomic DNA sequences were determined for two filamentous integrative bacteriophages, RSS1 and RSM1, of the phytopathogen Ralstonia solanacearum. The 6,662-base sequence of RSS1 contained 11 open reading frames (ORFs). In the databases, this sequence showed high homology (95% identity) to the circular double-stranded DNA plasmid pJTPS1 (6,633 bp) isolated from a spontaneously occurring avirulent mutant of R. solanacearum. Two major differences between the two sequences were observed within RSS1 ORF7, corresponding to pIII, a minor coat protein required for host adsorption, and at the RSS1 intergenic (IG) region. The 9,004-base sequence of RSM1 showed 12 ORFs located on the same strand (plus strand) and 2 ORFs on the opposite strand. Compared with Ff-type phages, two insertions are obvious in the RSM1 replication module. Genomic DNA fragments containing the RSM integration junctions were cloned and sequenced from RSM lysogenic strain R. solanacearum MAFF211270. The att core sequence was identified as 5-TGGCGGAGAGGGT-3, corresponding to the 3 end of the serine tRNA (UCG) gene. Interestingly, ORF14, located next to the attP site on the RSM1 genome, showed high amino acid sequence homology with bacterial DNA recombinases and resolvases, different from XerCD recombinases. attP of RSS1 is within a sequence element of the IG region.