The Filamentous Phage ϕRSS1 Enhances Virulence of Phytopathogenic Ralstonia solanacearum on Tomato

Abstract

Ralstonia solanacearum is the causative agent of bacterial wilt in many important crops. ϕRSS1 is a filamentous phage that infects R. solanacearum strains. Upon infection, it alters the physiological state and the behavior of host cells. Here, we show that R. solanacearum infected by ϕRSS1 becomes more virulent on host plants. Some virulence and pathogenicity factors, such as extracellular polysaccharide (EPS) synthesis and twitching motility, increased in the bacterial host cells infected with ϕRSS1, resulting in early wilting. Tomato plants inoculated with ϕRSS1-infected bacteria wilted 2 to 3 days earlier than those inoculated with wild-type bacteria. Infection with ϕRSS1 induced early expression of phcA, the global virulence regulator. phcA expression was detected in ϕRSS1-infected cells at cell density as low as 10(4) CFU/ml. Filamentous phages are assembled on the host cell surface and many phage particles accumulate on the cell surface. These surface-associated phage particles (phage proteins) may change the cell surface nature (hydrophobicity) to give high local cell densities. ϕRSS1 infection also enhanced PilA and type IV pilin production, resulting in increased twitching motility.

Genomic Analysis of Phylotype I Strain EP1 Reveals Substantial Divergence from Other Strains in the Ralstonia solanacearum Species Complex

“…Consistent with its largest genome size among the strains included in this study, strain EP1 contains ten unique insertion element genes, further supporting that the insertion elements play an important role in the evolution of bacterial genome, and may have contributed to the apparent diversity among R. solanacearum species. Previous results have demonstrated that bacteriophages are double-edged swords, they could either enhance or repress the virulence of R. solanacearum species and thus affect the outcome of pathogen-host interactions (Addy et al, 2012a,b). Similarly, the number and distribution of CRISPRs and bacteriophage sequences also differ in the strains of different phylotypes (Table S3, Table S4).…”

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

“…Assays of Egl activity and EPS. Total Egl activity was determined by measuring the reducing sugars (30) released during incubation of 20% (vol/vol) culture supernatant in 120 mM phosphate buffer (pH 7.0) with carboxymethylcellulose at 15 mg/ml as a substrate at 50°C for 4 h according to Addy et al (1). One unit of enzyme activity was defined as releasing glucose at 1 nmol/min.…”

Bacteriophage-Based Bacterial Wilt Biocontrol for an Environmentally Sustainable Agriculture

“…The filamentous bacteriophage φRSS1 (Yamada et al, 2007) was anew assayed to verify the efficacy of bacterial wilt biocontrol (Addy et al, 2012a) ( Table 1 ). In this case, when cells of the pathogen were infected with φRSS1 and injected into tomato plants, an increase in the bacterial virulence was observed, since the infection induced an early expression of the key regulatory phcA gene, interfering the main R. solanacearum quorum sensing system (Addy et al, 2012a).…”

“…In this case, when cells of the pathogen were infected with φRSS1 and injected into tomato plants, an increase in the bacterial virulence was observed, since the infection induced an early expression of the key regulatory phcA gene, interfering the main R. solanacearum quorum sensing system (Addy et al, 2012a). Thus, virulence and pathogenicity factors such as the synthesis of exopolysaccharide and the swimming motility increased in the φRSS1-infected bacterial cells, resulting in early wilting of the host (Addy et al, 2012a). However, filamentous bacteriophages can affect the bacterial wilt pathogen differently.…”