Isolation and characterization of two types of actinophage infecting Streptomyces scabies

Two types of actinophages, phiS and phiL, were isolated from soil samples by using Streptomyces scabies, a potato scab pathogen, as indicator strain. The phages were partially characterized according to their physicochemical properties, plaques and particles morphology, and their host range; this varied from narrow (for phiS) to wide (for phiL). The adsorption rate constants of the phiS and phiL were 3.44 and 3.18 pL/min, and their burst sizes were 1.61 and 3.75 virions per mL, respectively. One-step growth indicated that phiS and phiL have a latent period of 1/2 h followed by a rise period of 1/2 h. The temperate character of these phages was tested in other isolates of Streptomyces. Four of the phages ( phiSS3, phiSS12, phiSS13 and phiSS17) were identified as temperate phages, since they were able to lysogenize SS3, SS12, SS13 and SS17. phiSS3, phiSS12 and, phiSS13 were homoimmune, and they were heteroimmune with respect to SS17. The restriction barriers of lysogenic isolates (SS12, SS13 and SS17) interfered with the blockage of plaque formation by phages ( phiSS12, phiSS13 or phiSS17) propagated on them, about 75 \% of lysogenic isolates had restriction systems. The exposure of the lysogenic isolates (SS12, SS13 and SS17) to UV-irradiation prevented the possible restriction barriers of these isolates so that these barriers could be overcome.