CHARACTERIZATION OF A TEMPERATE BACTERIOPHAGE OF LACTOBACILLUS-DELBRUECKII SUBSP BULGARICUS AND ITS INTERACTIONS WITH THE HOST-CELL CHROMOSOME

The temperate bacteriophage mv4 is representative of a widespread phage genetic group of Lactobacillus delbrueckii subsp. lactis or bulgaricus. The genome of this phage is circularly permuted and terminally redundant, as shown by mature mv4 homoduplexes, Southern hybridization and restriction enzyme analysis. A circular map of the mv4 genome was established, with unique sequences totalling 36 kb. The genomic location of the pac site (packaging site of mv4 DNA into phage heads) and the att site (phage integration site into the host cell chromosome) was determined. The genes coding for the two main structural phage proteins and for a phage-associated lysin were also mapped. Phage mv4 is capable of transducing a limited set of pieces of bacterial DNA and several specific chromosomal attachment sites of phage mv4 were identified. Bacteria lysogenic for phage mv4 were shown to be immune to infection by L. delbrueckii virulent phages related to mv4.