A study of virus-host interactions in the genus Rhizobium

Various rhizobial strains were isolated which were sensitive to the virulent rhizobiophage, øC, and eight sensitive strains were tested for the presence of a restriction system. No restriction systems were found and variations in efficiencies of plating were attributable to adsorption phenomena and the selection of host range mutants. The virulent phage øC ,was found to have a broad host range because it plated on various rhizobial species, but even in interspecific phage growth studies no evidence of restriction was found. Several rhizobia were screened for bacteriocinogeny and lysogeny. No evidence was found for widespread bacteriocinogeny but one strain, G28, released a phage which plated on strain Gl8. The phage responsible (øS28) was temperate in G28 and Gl8. UV inactivation experiments suggested that øS28 had a genome size comparable with that of øC. The polylysogenic Su297/Su298 system was investigated. Su297 released a phage (øi) which plated on Su298 with low efficiency and the plaques produced on Su298 were due to a novel phage heteroimmune with øi. The novel phage (ø8) was temperate in Su297, contrary to the findings of previous workers. On infection of Su298 by øi another phage was released. This phage was ø7 and it was also heteroimmune with øi. The biogenesis of ø7 and ø8 was studied and from the data several criticisms were made about the interpretation of earlier data by other workers. A recombinational model for ø7 and ø8 biogenesis was presented to explain the observed host range of the various phages. Although transfection attempts proved totally ineffective, transduction attempts using the 07~related phages appeared to work. Analysis of the putative transductants revealed considerable heterogeneity in phage sensitivity patterns. A model was presented to explain the formation of such putative transductants