CHARACTERIZATION OF A TEMPERATE STREPTOCOCCUS-THERMOPHILUS BACTERIOPHAGE AND ITS GENETIC-RELATIONSHIP WITH LYTIC PHAGES

The temperate Streptococcus thermophilus bacteriophage phi SF121 showe d an 38-kb-long double-stranded DNA genome with cohesive ends. A singl e integration site was used in lysogens established in three different S. thermophilus strains. The attP and attB sites were localized on th e restriction map of phage DNA and by hybridization on pulsed field se parated bacterial DNA. All laboratory-established lysogens showed in a ddition to integrated prophage DNA unintegrated monomer phage DNA with unligated cos sites. The genetic relatedness of phi SFi21 DNA with DN A from lytic phages was studied in dot blot and Southern blot hybridiz ation by using individual restriction fragments of phi SFi21 DNA as pr obes. Lytic group I phages hybridized with fragments of the central an d the right part of the phi SFi21 genome but failed to hybridize with a fragment joining both parts. Lytic group II phages showed hybridizat ion with the right half of the phi SFi21 genome. In lytic group IV pha ges, biologically a heterogeneous group, many different combinations o f cross hybridization were detected in accordance with the hypothesis of the modular evolution of phage genomes. (C) 1995 Academic Press, In c.