Host recognition and integration of filamentous phage ϕRSM in the phytopathogen, Ralstonia solanacearum

Two prophages, called ϕRSM3 and ϕRSM4, that are closely related to, but differ from, filamentous phage ϕRSM1, have been detected in strains of the Ralstonia solanacearum species complex. The prophage ϕRSM3, found in host strain MAFF730139, could be converted to infectious phage by means of PCR and transfection. The nucleotide sequence of ϕRSM3 is highly conserved relative to ϕRSM1 except for open reading frame 2 (ORF2), encoding an unknown protein, and ORF9 encoding the presumed adsorption protein that determines host range. The two host ranges differ dramatically and correlate closely with different gel electrophoresis banding patterns for cell surface fimbriae. Infections by ϕRSM1 and ϕRSM3 enhance bacterial cell aggregation and reduce the bacterial host virulence in tomato plants. Database searches in the R. solanacearum strains of known genomic sequence revealed two inovirus prophages, one designated ϕRSM4 that is homologous to ϕRSM1 and ϕRSM3, and one homologues to RSS1, in the genome of strain UW551.