Identification and characterization of a lysis module present in a large proportion of bacteriophages infecting Streptococcus thermophilus

A lysis module encoded by the temperate bacteriophage phi O1205 was identif ied. This lysis module contains a lysin gene, designated lyt51, and two put ative holin-encoding genes, designated lyt49 and lyt50. lyt51 encodes a lyt ic enzyme specifically directed against streptococcal cell walls. Similar t o other phage-encoded lysins, Lyt51 appears to have a modular design in whi ch the N-terminal portion corresponds to its enzymatic activity while the C -terminal region is responsible for its substrate binding specificity. The two putative holin-encoding genes, lyt49 and lyt50, located immediately ups tream of lyt51, were identified on the basis of their homology to other ide ntified holin-encoding genes. Expression of lyt49 or lyt50 in Escherichia c all was shown to cause cell death and leakage of the intracellular enzyme i socitrate dehydrogenase into the growth medium without apparent lysis of th e cells. Southern blotting experiments demonstrated that at least one of th e three components of the identified lysis module is present in all members of a large collection of bacteriophages, indicating that components of thi s lysis module are widespread among bacteriophages infecting Streptococcus thermophilus.