FIG. 4.

Screening of S. thermophilus bacteriophages and starter cultures for the presence of the S3b-type intron. (A) PCR amplification with primer pair C-D1 (or, alternatively, C-D2 in the case of nonannealing of D1) and the following phage DNAs as templates: S93, Sfi16A, S3b, Sfi21, S92, and ST64 (lanes a to f, respectively). The sizes of the DNA products obtained for S3b and Sfi21 are shown in base pairs. (B) Dot blot of S. thermophilus bacteria and bacteriophage DNA with S3b intron DNA as a probe. (A) Lanes 1 to 12, Sfi phages 21, 11, 13, 16A, 18, 19, and 121 and HN phages 1, 4, 6, 7, and 9. (B) Lanes 1 to 12, ST phages 1, 2, 3, 9, 12, 13, 20, 30, 40, 41, 42, and 44. (C) Lanes 1 to 5, ST phages 64, 72, 84, 128, and J1; lanes 7 to 12, TN starter cultures 2, 17, 36, 44, 21, and 62. (D) Lanes 1 to 12, S phages 3b, 1, 2, 3, 5, 6, 7, 8, 9, 10, 11, and 12. (E) Lanes 1 to 10 and 12, phages 13, 14, 15, 17, 18, 19, 56, 66, 77, 89, and 94. (F) Lanes 1 and 2, S phages 96 and 97; lanes 6 to 12, TN starter cultures 49, 70, 39, 41, 42, 45, and 58. (G) Lanes 1 to 12, Sfi starter cultures 1, 2, 3, 6, 8, 10, 11, 13, 16, 18, 19, and 20. (H) Lanes 1 to 5, Sfi starter cultures 25, 26, 39, 41, and IL; lanes 7 to 9, S starter cultures 3, 17, and 97. (C) Southern hybridization with the phage S3 intron DNA as a probe. Lanes a to c, PvuII-digested genomic DNAs from phages S18, S89, and S94; lane d, HindIII-digested DNA from phage S3b. Molecular sizes for the signals in lanes a to d were approximately 8.5, 12, 7, and 3.5 kb, respectively.