Molecular and biological characterization of [PHI]Rs551, a filamentous bacteriophage isolated from a race 3 biovar 2 strain of Ralstonia solanacearum

• Published in: PloS one 2017-09, Vol.12 (9), p.e0185034
• Main Authors: Ahmad, Abdelmonim Ali, Stulberg, Michael J, Mershon, John Patrick, Mollov, Dimitre S, Huang, Qi
• Format: Article
• Language: English
• Subjects: Bacteriophages; Genetic aspects; Physiological aspects; Phytopathogenic bacteria; Structure
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0185034

A filamentous bacteriophage, designated [PHI]Rs551, was isolated and purified from the quarantine and select agent phytopathogen Ralstonia solanacearum race 3 biovar 2 strain UW551 (phylotype IIB sequevar 1) grown under normal culture conditions. Electron microscopy suggested that [PHI]Rs551 is a member of the family Inoviridae, and is about 1200 nm long and 7 nm wide. [PHI]Rs551 has a genome of 7929 nucleotides containing 14 open reading frames, and is the first isolated virion that contains a resolvase (ORF13) and putative type-2 phage repressor (ORF14). Unlike other R. solanacearum phages isolated from soil, the genome sequence of [PHI]Rs551 is not only 100% identical to its prophage sequence in the deposited genome of R. solanacearum strain UW551 from which the phage was isolated, but is also surprisingly found with 100% identity in the deposited genomes of 10 other phylotype II sequevar 1 strains of R. solanacearum. Furthermore, it is homologous to genome RS-09-161, resulting in the identification of a new prophage, designated RSM10, in a R. solanacearum strain from India. When ORF13 and a core attP site of [PHI]Rs551 were either deleted individually or in combination, phage integration was not observed, suggesting that similar to other filamentous R. solanacearum [PHI]RSM phages, [PHI]Rs551 relies on its resolvase and the core att sequence for site-directed integration into its susceptible R. solanacearum strain. The integration occurred four hours after phage infection. Infection of a susceptible R. solanacearum strain RUN302 by [PHI]Rs551 resulted in less fluidal colonies and EPS production, and reduced motilities of the bacterium. Interestingly, infection of RUN302 by [PHI]Rs551 also resulted in reduced virulence, rather than enhanced or loss of virulence caused by other [PHI]RSM phages. Study of bacteriophages of R. solanacearum would contribute to a better understanding of the phage-bacterium-environment interactions in order to develop integrated management strategies to combat R. solanacearum.