Evidence for temperate bacteriophages in two strains ofLactobacillus bulgaricus

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Abstract
Summary: Lactobacillus bulgaricusstrains LT1 and LT4 previously isolated from a yogurt factory were shown to be lysogenic and inducible by mitomycin C or u.v. irradiation, induction being optimal at the beginning of exponential growth. Five indicator strains (four ofL. lactis, one ofL. bulgaricus) were found in which the two phage lysates propagated well in a liquid medium, but formed plaques on bacterial lawns less readily. Ca2+was required for the phage infection of the indicator strains to reach termination. Phage particles from each strain exhibited a comparable ultrastructural morphology under the electron microscope, having an isometric head, a triple collar and a noncontractile fibre-containing tail.