Loss of Virulence of the Phytopathogen Ralstonia solanacearum Through Infection by φRSM Filamentous Phages

Department of Molecular Biotechnology, Hiroshima University, Higashi-Hiroshima, Japan.
Phytopathology (Impact Factor: 3.12). 02/2012; 102(5):469-77. DOI: 10.1094/PHYTO-11-11-0319-R
Source: PubMed


φRSM1 and φRSM3 (φRSM phages) are filamentous phages (inoviruses) that infect Ralstonia solanacearum, the causative agent of bacterial wilt. Infection by φRSM phages causes several cultural and physiological changes to host cells, especially loss of virulence. In this study, we characterized changes related to the virulence in φRSM3-infected cells, including (i) reduced twitching motility and reduced amounts of type IV pili (Tfp), (ii) lower levels of β-1,4-endoglucanase (Egl) activity and extracellular polysaccharides (EPS) production, and (iii) reduced expression of certain genes (egl, pehC, phcA, phcB, pilT, and hrpB). The significantly lower levels of phcA and phcB expression in φRSM3-infected cells suggested that functional PhcA was insufficient to activate many virulence genes. Tomato plants injected with φRSM3-infected cells of different R. solanacearum strains did not show wilting symptoms. The virulence and virulence factors were restored when φRSM3-encoded orf15, the gene for a putative repressor-like protein, was disrupted. Expression levels of phcA as well as other virulence-related genes in φRSM3-ΔORF15-infected cells were comparable with those in wild-type cells, suggesting that orf15 of φRSM3 may repress phcA and, consequently, result in loss of virulence.

68 Reads
  • Source
    • "ORFs shown in green, red, and black are genes encoding an integrase (Int), transcriptional repressor, and φRSS1-ORF11-like ORF, respectively. such as extracellular polysaccharides (EPSs) in Xf-or Lf-infected Xanthomonas campestris (Kamiunten and Wakimoto, 1982; Tseng et al., 1990), (ii) induction of biofilm formation in Pf4- producing Pseudomonas aeruginosa (Webb et al., 2004; Rice et al., 2009), and (iii) reduced twitching motility in φRSM-infected Ralstonia solanacearum (Addy et al., 2012a) and in XacF1- infected X. citri (Ahmad et al., 2014). These are likely caused by changes in the host cell surface where phage proteins are secreted and filamentous particles are assembled. "
    [Show description] [Hide description]
    DESCRIPTION: Two different evolutionary lines of filamentous phages in Ralstonia solanacearum: their effects on bacterial virulence
  • Source
    • "Temperate phages have been found in many phytopathogens and plant-associated bacteria such as Rhizobium spp. (Malek, 1990; Uchiumi et al., 1998), Ralstonia solanacearum (Yamada et al., 2007; Murugaiyan et al., 2011; Addy et al., 2012a,b), rhizosphere pseudomonads (Shaburova et al., 2000), Xanthomonas campestris pv. azadirachtae (Borkar, 1997), Erwinia carotovora subsp. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Lytic bacteriophages are in development as biological control agents for the prevention of fire blight disease caused by Erwinia amylovora. Temperate phages should be excluded as biologicals since lysogeny produces the dual risks of host resistance to phage attack and the transduction of virulence determinants between bacteria. The extent of lysogeny was estimated in wild populations of E. amylovora and Pantoea agglomerans with real-time polymerase chain reaction primers developed to detect E. amylovora phages belonging to the Myoviridae and Podoviridae families. Pantoea agglomerans, an orchard epiphyte, is easily infected by Erwinia spp. phages, and it serves as a carrier in the development of the phage-mediated biological control agent. Screening of 161 E. amylovora isolates from 16 distinct geographical areas in North America, Europe, North Africa and New Zealand and 82 P. agglomerans isolates from southern Ontario, Canada showed that none possessed prophage. Unstable phage resistant clones or lysogens were produced under laboratory conditions. Additionally, a stable lysogen was recovered from infection of bacterial isolate Ea110R with Podoviridae phage ΦEa35-20. These laboratory observations suggested that while lysogeny is possible in E. amylovora, it is rare or absent in natural populations, and there is a minimal risk associated with lysogenic conversion and transduction by Erwinia spp. phages. © 2015 The Authors. Microbial Biotechnology published by John Wiley & Sons Ltd and Society for Applied Microbiology.
    Microbial Biotechnology 02/2015; 8(3). DOI:10.1111/1751-7915.12253 · 3.21 Impact Factor
  • Source
    • "Recent reports propose that bacterial adhesion and motility are required in the initial stages of Xac biofilm formation, whereas lipopolysaccharide and EPS play important roles in the establishment of mature biofilms (Li and Wang, 2011). The reduction in motility of XacF1-infected cells may be because filamentous phages such as XacF1 assemble on the host cell membrane and protrude from the cell surface, and so the nature of the host cell surface may change drastically during phage production (Addy et al., 2012). As shown in Supplemental Figure S1, XacF1-infected cells had considerably decreased levels of PilA, the major component of type IV pili. "
    [Show abstract] [Hide abstract]
    ABSTRACT: In this study, filamentous phage XacF1, which can infect Xanthomonas axonopodis pv. citri (Xac) strains, was isolated and characterized. Electron microscopy showed that XacF1 is a member of the family Inoviridae and is about 600 nm long. The genome of XacF1 is 7325 nucleotides in size, containing 13 predicted open reading frames (ORFs), some of which showed significant homology to Ff-like phage proteins such as ORF1 (pII), ORF2 (pV), ORF6 (pIII), and ORF8 (pVI). XacF1 showed a relatively wide host range, infecting seven out of 11 strains tested in this study. Frequently, XacF1 was found to be integrated into the genome of Xac strains. This integration occurred at the host dif site (attB) and was mediated by the host XerC/D recombination system. The attP sequence was identical to that of Xanthomonas phage Cf1c. Interestingly, infection by XacF1 phage caused several physiological changes to the bacterial host cells, including lower levels of extracellular polysaccharide production, reduced motility, slower growth rate, and a dramatic reduction in virulence. In particular, the reduction in virulence suggested possible utilization of XacF1 as a biological control agent against citrus canker disease.
    Frontiers in Microbiology 07/2014; 5:321. DOI:10.3389/fmicb.2014.00321 · 3.99 Impact Factor
Show more