New bacteriophages that infect the phytopathogen Ralstonia solanacearum

Abstract

Four kinds of bacteriophage (wRSL, wRSA, wRSM and wRSS) were isolated from Ralstonia solanacearum, a soil-borne Gram-negative bacterium that is the causative agent of bacterial wilt in many important crops. The Myovirus-type phages wRSL1 and wRSA1 contained dsDNA genomes of 240 kbp and 39 kbp, respectively. These phages have relatively wide host ranges and gave large clear plaques with various host strains; especially wRSA1 was able to infect all 15 R. solanacearum strains of different races or different biovars tested in this study. Three host strains contained wRSA1-related sequences in their genomic DNAs, suggesting a lysogenic cycle of wRSA1. Two phages, wRSM1 and wRSS1, were characterized as Ff-type phages (Inovirus) based on their particle morphology, genomic ssDNA and infection cycle. However, despite their similar fibrous morphology, their genome size (9.0 kb for wRSM1 and 6.6 kb for wRSS1) and genome sequence were different. Strains of R. solanacearum that were sensitive to wRSM1 were resistant to wRSS1 and vice versa. Several R. solanacearum strains contained wRSM1-related sequences and at least one strain produced wRSM1 particles, indicating the lysogenic state of this phage. These phages may be useful as a tool not only for molecular biological studies of R. solanacearum pathogenicity but also for specific and efficient detection (wRSM1 and wRSS1) and control of harmful pathogens (wRSL and wRSA) in cropping ecosystems as well as growing crops.

Bacteriophages of Ralstonia solanacearum: Their Diversity and Utilization as Biocontrol Agents in Agriculture

“…A similar prophage found in Ralstonia pickettii 12J is also shown. Genomic Southern blot hybridization showed frequent examples of RSS1-related sequences integrated in the genomes of various R. solanacearum strains (Yamada et al, 2007). As seen above, RSS2 is integrated in the genome of strain M4S.…”

“…Interestingly, this internal region of RSM3 (also 67% identical in RSM4) shows a significant similarity (79%) to the corresponding region of RSS1, which shows a different host range from RSM1 (Yamada et al, 2007). These results predict that RSM3 and RSM4 share a common host range, which differs from that of RSM1, and suggest that the host range determined by the pIII-D2 domain may be exchangeable among phages.…”

“…As seen above, RSS2 is integrated in the genome of strain M4S. RSS1 was also found to exist as a lysogenic phage in strain C319 (Kawasaki et al, 2007). By analyzing the host genomic sequences flanking the RSS1 region, its integration site was determined to correspond to RSS1 position 6,629 in the IG region, 34 nt upstream from ORF1.…”

“…Various kinds of bacteriophage with characteristic features have been isolated recently (Yamada et al, 2007), and have paved the way for new methods of biocontrol of bacterial wilt. These phages may be useful as tools for effective detection (diagnosis) of the pathogen in cropping ecosystems and in growing crops.…”

Chimeric viruses blur the borders between the major groups of eukaryotic single-stranded DNA viruses

“…ssDNA viruses infecting plants (geminiviruses and nanoviruses) and animals (anelloviruses, circoviruses and parvoviruses) were in the spotlight of extensive research for many years due to their direct effect on the well-being of humans. Recently, a previously unsuspected facet of the ssDNA viruses as important factors in the global ecosystems has come to light; viruses with ssDNA genomes have been repeatedly isolated from diverse environments, including extreme geothermal 2 and hypersaline habitats 3,5 , soil 6 , freshwater and marine ecosystems [7][8][9] .…”