Browsing by Subject "Cystovirus"

In this study the host range of cystoviruses was explored. Cystoviruses are bacteriophages belonging to the Cystoviridae family. They are enveloped, tri-segmented double-stranded RNA viruses which mainly infect plant pathogenic Pseudomonas syringae strains. Thus, they could potentially be used in phage therapy applications to treat bacterial infections. Before phage therapy can be implemented, the host range dynamics of the cystoviruses need to be understood to ensure that they do not affect the growth of harmless or beneficial bacteria. Cystoviruses have also been used as safe RNA virus models to study factors contributing to virus host range shifts and viral fitness. The first aim of this study was to analyse the host range of cystoviruses phi6, phiNN, phi8, phi12, phi13 and phi2954 by spot test assay. A reverse genetics method was used to detect whether the host range of cystoviruses expands, when the host entry step is bypassed. It was necessary to use derivatives of the potential host strains that contain a plasmid for T7 polymerase expression. As a control, such cell lines were also directly infected with the studied phages. Also, the ability of phages phi6 and phiNN to evolve to infect each other's isolation hosts was studied as well as the frequency and the fitness of the host range mutants was analysed by traditional plating assay. This study provides new information about the host ranges of the cystoviruses. All cystoviruses were shown to have a unique host range pattern with phi6 and phiNN having the widest host ranges. The reverse genetics method allowed cystoviruses phi6, phi8, phi13 and phi2954 to expand their host ranges but subsequent control experiments raised questions as to whether the plasmid containing T7 polymerase gene had a role in this. Both phi6 and phiNN evolved to infect each other´s isolation hosts but the frequency of these host range mutants was lower than has been reported for phi6 in previous studies. It was also demonstrated that the expansion of the host range often imposed fitness costs on the original host.