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Characterization of Ralstonia solanaceraum phage Rs-USA-M1 isolated from a tomato field in Florida, USA

Abdelmonim Ali Ahmad: Floral and Nursery Plants Research Unit, U. S. National Arboretum, USDA/ARS

<div><em>Ralstonia solanacearum</em> is one of the most destructive plant pathogenic bacteria in the world. In order to control this bacterium, efforts have been made to explore the possibility of using bacteriophages as an alternative control strategy. In this study, we report the isolation of a <em>R. solanacearum</em>-infecting phage, designated as phage Rs-USA-M1, from a tomato field in Florida, USA. Electron microscopy revealed that phage Rs-USA-M1 is a member of the family <em>Myoviridae</em> with a long “neck”. The phage infected 13 out of 31 tested <em>R. solanacearum </em><em>strains. It had a burst time of about 180 minutes releasing </em>approximately 56 plaque-forming units per cell. The phage has a genome size of 39,309 nucleotides (nt) containing 58 open reading frames. It also contains a 45-nt tRNA-like sequence as a probable attachment <em>att</em>P site, which is well-aligned within a 76-nt threonine tRNA sequence from <em>R. solanacearum</em> strain 23-10BR, GMI1000, K60, or Po82. Phylogenetic analysis based on the amino acid sequence of the large terminase, portal, or head protein revealed that phage Rs-USA-M1 belongs to the subfamily Peduovirinae and the Genus P2virus, and is most closely related to <em>Ralstonia</em> phage RSA1. However, the phage Rs-USA-M1 differs from phage RSA1 in amino acid sequence of the integrase, suggesting that the former is a variant of the latter. The potential of using phage Rs-USA-M1 as a biocontrol agent for <em>R. solanacearum</em> is currently being studied and will be discussed.</div>