DISTINCT STREPTOCOCCUS-THERMOPHILUS BACTERIOPHAGES SHARE AN EXTREMELY CONSERVED DNA FRAGMENT

A cross-hybridizing 2.2-kb EcoRI fragment was cloned from two lytic Streptococcus thermophilus bacteriophages with distinct phenotypes. The DNA fragments, which contained two unidentified open reading frames, differed at only 3 of 2207 nucleotide positions. Partial sequencing of a temperate S. thermophilus phage and of a further lyric phage belonging to a different lytic group isolated 20 years earlier from a different geographical area confirmed this extreme sequence conservation. Hybridization of this phage DNA with bacterial host DNA was not observed. The evolutionary implications of these observations are briefly discussed. (C) 1994 Academic Press, Inc.