Genomic Characterization of Filamentous Integrative Bacteriophages, RSS1 and RSM1, That Infect Ralstonia solanacearum

Department of Molecular Biotechnology, Graduate School of Advanced Sciences of Matter, Hiroshima University, Higashi-Hiroshima 739-8530, Japan

^* To whom correspondence should be addressed. Email: tayamad{at}hiroshima-u.ac.jp.

	Abstract

The genomic DNA sequences were determined for two filamentous integrative bacteriophages, RSS1 and RSM1, of the phytopathogen Ralstonia solanacearum. The 6,662 b sequence of RSS1 contained 11 open reading frames (ORFs). In the databases, this sequence showed high homology (95% identity) to the circular dsDNA 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 the RSS1 ORF7 corresponding to pIII, a minor coat protein required for host adsorption, and at the RSS1 intergenic (IG) region. The 9,004 b sequence of RSM1 showed 12 ORFs located on the same strand (plus strand) and two 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 the 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/resolvases, different from XerCD recombinases. The attP of RSS1 is within a sequence element of the IG.