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 1b539 with mitomycin C as well as the sensitivity of 1b539 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 1b539 was classified within Bradley's B1 phage group and the Siphoviridae family. The host range of 1b539 encompassed mainly Lactobacillus delbrueckii ssp. lactis strains; strain LKT (CNRZ 700) was the most sensitive for detection of 1b539 lysates induced by mitomycin C. The 1b539 genome is a linear, double-stranded DNA molecule of approximately 35 kbp. The presence of submolar fragments in restriction enzyme digests suggests that 1b539 DNA may contain a pac site. Dot-blot experiments showed that the 1b539 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 1b539 to be distinct from mv4 and LL-H.