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J. Bacteriol. doi:10.1128/JB.01158-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Genomic Characterization of Ralstonia solanacearum Phage RSA1 and Its Related Prophage (RSX) in Strain GMI1000

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

RSA1 is a wide-host range bacteriophage isolated from Ralstonia solanacearum. In this study, the complete nucleotide sequence of the RSA1 genomic DNA was determined. The genome was 38,760 bp dsDNA (65.3% G+C) with 19 bp 5'-extruding cohesive ends (cos) and contained 51 open reading frames (ORFs). Two thirds of the RSA1 genomic region encode the phage structural modules and are very similar to those reported for coliphage P2 and P2-like phages. A mini-RSA1 replicon with a 8.2 kbp early-expressing region was constructed. A late expression promoter sequence motif was predicted for these RSA1 genes as 5' TGTTGT-(X)₁₃-ACAACA. The genomic sequence similarity between RSA1 and related phages 52237 or CTX was interrupted by three AT-islands, one of which contained an IS element, suggesting that they were recombinational hot spots. RSA1 was found to be integrated in at least three different strains of R. solanacearum and the chromosomal integration site (attB) was identified as the 3' portion of arginine tRNA (CCG) gene. In the light of the RSA1 gene arrangement, one possible prophage sequence previously detected on the chromosome of R. solanacearum strain GMI1000 was characterized to be a RSA1-related prophage (designated as RSX). RSX was found to be integrated at the serine tRNA (GGA) gene as att site and its size was determined to be 40,713 bp. RSX ORFs shared very high amino acid identity with RSA1 counterparts. The relationships and evolution of these P2-like phages are discussed.