SUMMARY: Three phages, isolated from soil samples collected in different localities, produced turbid plaques with a characteristic morphology on A3(2). Surviving growth from the plaques was lysogenic: when isolated and purified it was resistant to lysis by the homologous phage and released phage at a low frequency during growth. The three phages were homoimmune. The chromosomal attachment site of one of the prophages, VP5, was mapped in a position between and - that is, in a region devoid of standard markers - on the circular linkage map of the host, by crossing defective lysogens with sensitive strains. The host range of VP5 was restricted; only certain strains belonging to the group were attacked. VP5 gave rise to clear-plaque mutants, incapable of lysogenizing the host, at a spontaneous frequency of 10, which was increased by u.v. irradiation and by hydroxylamine mutagenesis; the clear-plaque mutants were incapable of lysing strains carrying the wild-type prophage. Electron microscopy showed that VP5 belongs to group B of Bradley's morphological classification.


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