Isolation and Characterization of a New Lactobacillus delbrueckii ssp. bulgaricus Temperate Bacteriophage

Lactobacillus delbrueckii ssp. bulgaricus strain CRL 539 was shown to be lysogenic and inducible with mitomycin C. The conditions were determined for an optimal induction of temperate bacteriophage lb539 with mitomycin C as well as the sensitivity of lb539 to physical and chemical agents. Electron microscopy of lysates revealed bacteriophage particles with an isometric head of 47 nm and a noncontractile tail of 159 nm. Phage lb539 was classified within Bradley's B1 phage group and the Siphoviridae family. The host range of lb539 encompassed mainly Lactobacillus delbrueckii ssp. lactis strains; strain LKT (CNRZ 700) was the most sensitive for detection of lb539 lysates induced by mitomycin C. The lb539 genome is a linear, double-stranded DNA molecule of approximately 35 kbp. The presence of submolar fragments in restriction enzyme digests suggests that lb539 DNA may contain a pac site. Dotblot experiments showed that the lb539 genome hybridized with the genomes of phages mv4 and LL-H, which are type phages of group a of L. delbrueckii ssp. phages. Restriction enzyme patterns and morphological features showed lb539 to be distinct from mv4 and LL-H.