Isolation and Examination of Transducing Particles from Streptococcus lactis C21,2

Abstract

Two defective transducing bacteriophages induced by exposure of Streptococcus lactis C2 to ultraviolet irradiation have been isolated and characterized. These temperate phages designated c2t1 and c2t2 were isolated by cesium chloride equilibrium density gradient centrifugation of phage preparations concentrated by polyethylene glycol precipitation. The equilibrium gradient contained two visually apparent phage bands positioned at densities of 1.487 and 1.463g cm-3 respective for c2t1 and c2t2. Particle morphology and phenol extracted phage deoxyribonucleic acid were examined by electron microscopy for each phage. Head diameter, deoxyribonucleic acid length, and molecular weight for c2t1 were 60nm, 10.9μm, and 22.6×106 daltons, respectively. Phage c2t2 had a head diameter of 70nm, a deoxyribonucleic acid length of 11.4μm, and a molecular weight of 23.8×10 daltons. Comparing head diameter and phage deoxyribonucleic acid length suggests that the variation in c2t1 and c2t2 density was due to difference in head size. Phage c2t2 exhibited high frequency transduction of lactose metabolism based on preparations equilibrated by adjustment of optical density at 260nm. Maltose and proteinase markers also were transduced by both phages. The transducing phage was defective, requiring a helper for the formation of transducing particles but not for the transduction process. Superinfection immunity was not conferred on post-infecting phage. The results demonstrated transduction by two nonidentical phage particles lysogenic for S. lactis C2.