Biological and Molecular Characterization of a Jumbo Bacteriophage Infecting Plant Pathogenic Ralstonia solanacearum Species Complex Strains.

Abdelmonim Ali Ahmad,Hardian Susilo Addy,Qi Huang

doi:10.3389/fmicb.2021.741600

Abstract

A jumbo phage infecting Ralstonia solanacearum species complex strains, designated RsoM2USA, was isolated from soil of a tomato field in Florida, United States, and belongs to the family Myoviridae. The phage has a long latent period of 270 min and completed its infection cycle in 360 min with a burst size of approximately 32 particles per cell. With a genome size of 343,806 bp, phage RsoM2USA is the largest Ralstonia-infecting phage sequenced and reported to date. Out of the 486 ORFs annotated for RsoM2USA, only 80 could be assigned putative functions in replication, transcription, translation including 44 tRNAs, and structure with the main structural proteins experimentally confirmed. Phylogenetic analyses placed RsoM2USA in the same clade as Xanthomonas phage XacN1, prompting a proposal of a new genus for the two jumbo phages. Jumbo phage RsoM2USA is a lytic phage and has a wide host range, infecting each of the three newly established Ralstonia species: R. solanacearum, R. pseudosolanacearum, and R. syzygii, and significantly reduced the virulence of its susceptible R. solanacearum strain RUN302 in tomato plants, suggesting that this jumbo phage has the potential to be developed into an effective control against diseases caused by R. solanacearum species complex strains.

Highlights

Ralstonia solanacearum species complex (Rssc) strains are soilborne vascular bacterial plant pathogens and have recently been split into three different Ralstonia species: R. solanacearum, R. pseudosolanacearum, and R. syzygii (Safni et al, 2014)
We report the discovery and characterization of a jumbo phage with a genome of more than 343 kb in size isolated from soil in the United States that infects pathogenic R. solanacearum, R. pseudosolanacearum, and syzygii strains
A pure phage designated RsoM2USA was isolated from soil obtained from a tomato field infested by R. solanacearum strains in Florida, United States, using R. solanacearum strain RUN302 as a bacterial host and the triple phage purification process described by Addy et al (2019)

Summary

Introduction

Ralstonia solanacearum species complex (Rssc) strains are soilborne vascular bacterial plant pathogens and have recently been split into three different Ralstonia species: R. solanacearum, R. pseudosolanacearum, and R. syzygii (Safni et al, 2014). They cause bacterial wilt in over 44 plant families and are a major limiting factor in the production of many economically important crops including tomato, potato, and tobacco around the world (Hayward, 1991). Ralstonia Jumbo Phage RsoM2USA normally enter a host plant from soil through wounds in plant roots They multiply in the xylem of the plant and move through the vascular system (Vasse et al, 1995). Phage application to soil pathogens like Rssc in humid tropical environments could minimize phage exposure to desiccation and UV light, increasing the likelihood for their success in biocontrol

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Conclusion