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

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 10⁴ 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.