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.

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    • "Ralstonia solanacearum. Here, phage infection reduces the bacteria's virulence in host plant tissues by limiting the expression of bacterial virulence factors (Addy et al., 2012). In these cases the hyperparasite actively reduces the damage caused by the pathogen, thus reducing the pathogen's virulence below the evolved optima. "
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    ABSTRACT: Many micro-organisms employ a parasitic lifestyle and, through their antagonistic interactions with host populations, have major impacts on human, agricultural and natural ecosystems. Most pathogens are likely to host parasites of their own, that is, hyperparasites, but how nested chains of parasites impact on disease dynamics is grossly neglected in the ecological and evolutionary literature. In this minireview we argue that the diversity and dynamics of micro-hyperparasites are an important component of natural host-pathogen systems. We use the current literature from a handful of key systems to show that observed patterns of pathogen virulence and disease dynamics may well be influenced by hyperparasites. Exploring these factors will shed light on many aspects of microbial ecology and disease biology, including resistance-virulence evolution, apparent competition, epidemiology and ecosystem stability. Considering the importance of hyperparasites in natural populations will have applied consequences for the field of biological control and therapeutic science, where hyperparastism is employed as a control mechanism but not necessarily ecologically understood.
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    • "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. "
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    DESCRIPTION: Two different evolutionary lines of filamentous phages in Ralstonia solanacearum: their effects on bacterial virulence
    Full-text · Research · Jul 2015
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    • "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. "
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    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.
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