Genomic diversity of large-plaque-forming podoviruses infecting the phytopathogen Ralstonia solanacearum

Abstract

The genome organization, gene structure, and host range of five podoviruses that infect Ralstonia solanacearum, the causative agent of bacterial wilt disease were characterized. The phages fell into two distinctive groups based on the genome position of the RNA polymerase gene (i.e., T7-type and ϕKMV-type). One-step growth experiments revealed that ϕRSB2 (a T7-like phage) lysed host cells more efficiently with a shorter infection cycle (ca. 60 min corresponding to half the doubling time of the host) than ϕKMV-like phages such as ϕRSB1 (with an infection cycle of ca. 180 min). Co-infection experiments with ϕRSB1 and ϕRSB2 showed that ϕRSB2 always predominated in the phage progeny independent of host strains. Most phages had wide host-ranges and the phage particles usually did not attach to the resistant strains; when occasionally some did, the phage genome was injected into the resistant strain's cytoplasm, as revealed by fluorescence microscopy with SYBR Gold-labeled phage particles.

Potential use of soilborne lytic Podoviridae phage as a biocontrol agent against Ralstonia solanacearum

“…In Japan ϕRSB1, ϕRSB2, ϕRSB3 ϕRSJ2, and ϕRSJ5 podoviruses were previously isolated against R. solanacearum and identified by ref. . Electron microscopic examination of R. solanacearum phage particles ϕRSB1, ϕRSB2, ϕRSB3, ϕRSJ2, and ϕRSJ5 showed a virion structure similar to T7‐like phages that belong to Podoviridae family with short‐tailed icosahedral, and head diameter of nearly 60 nm and short‐thick tail ranging of 8–10 nm in length .…”

“…. Electron microscopic examination of R. solanacearum phage particles ϕRSB1, ϕRSB2, ϕRSB3, ϕRSJ2, and ϕRSJ5 showed a virion structure similar to T7‐like phages that belong to Podoviridae family with short‐tailed icosahedral, and head diameter of nearly 60 nm and short‐thick tail ranging of 8–10 nm in length . RsPod1EGY phage has shown to belong to the Podoviridae family, order Caudovirales .…”

“…In the case of ϕRSB2, phage infection happened with R. solanacearum strains (MAFF 730138), with an infection cycle of 60 min and a latent period of 40 min, giving a burst size of ca. 30 PFU/cell . Phage characteristics such as heat and pH sensitivity are important factors for the application of the phage in different environments for biological control.…”

Characterization of CRISPR‐Cas systems in the Ralstonia solanacearum species complex

“…Bacteriophages belonging to four viral families ( Podoviridae , Myoviridae , Siphoviridae and Inoviridae ) have been described infecting RSSC strains, and some have shown promise for the control of bacterial wilt disease (Addy et al , ; Elhalag et al , ; Kawasaki et al , , ; Liao, ; Ozawa v, ; Su et al , ; Toyoda et al , ; Van Truong Thi et al , ; Yamada, ) Nevertheless, more studies are needed for a future implementation of phage therapy in the fight against this destructive plant disease (Álvarez and Biosca, ).…”

“…Bacteria use a wide range of strategies to evade viral infection (Labrie et al , ), including the immune adaptive CRISPR‐Cas [clustered regularly interspaced short palindromic repeat (CRISPR) and CRISPR‐associated (Cas)] system (Barrangou and Horvath, ). In the RSSC, natural resistance to viral infection has been observed, but the variability in resistance phenotypes suggests the involvement of more than one defence mechanism (Kawasaki et al , ).…”