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Characterization of the cro-ori region of the Streptococcus thermophilus virulent bacteriophage DT1

Geneviève Lamothe1, Céline Lévesque, Frédéric Bissonnette

  • 1Groupe de Recherche en Ecologie Buccale, Faculté de Médecine Dentaire, Université Laval, Québec, Canada G1K 7P4.

Applied and Environmental Microbiology
|March 5, 2005
PubMed

Insights

The origin of replication (ori) from Streptococcus thermophilus phage DT1 confers phage resistance to bacterial strains during milk fermentation. This protection is specific to the phage and dependent on the bacterial strain.

Area of Science:

  • Microbiology
  • Bacteriology
  • Virology

Background:

  • Streptococcus thermophilus phage DT1, a virulent cos-type phage, has a fully sequenced genome.
  • A putative origin of replication (ori) with repeat sequences was identified.
  • The replication ability of the ori and its flanking genes was unconfirmed.

Purpose of the Study:

  • To investigate the phage resistance conferred by the putative ori of phage DT1.
  • To establish a transcriptional map of the region between a cro-like gene (orf29) and the ori.
  • To compare the expression of this region across different S. thermophilus phages.

Main Methods:

  • Cloning the ori onto a high-copy-number plasmid to test phage resistance.
  • Northern blot analysis to determine transcriptional patterns.
  • Primer extension and chloramphenicol acetyltransferase (CAT) assays to characterize promoter activity.

Main Results:

  • Cloned ori provided phage resistance to S. thermophilus during milk fermentation, demonstrating strain and phage specificity.
  • Transcription initiated 5 minutes post-infection, with distinct transcript profiles observed for phages DT1, Sfi19, and Sfi21.
  • The phage promoter upstream of orf29 was active and more efficient than the S. thermophilus phosphoenolpyruvate:sugar phosphotransferase (pts) promoter, but less efficient than pts promoters in Lactococcus lactis and Escherichia coli.

Conclusions:

  • The ori of phage DT1 can confer phage resistance in S. thermophilus, offering potential applications in controlling phage infections in dairy fermentation.
  • Transcriptional analysis revealed specific expression patterns for the cro-ori region in different phages.
  • The phage promoter exhibits significant activity, highlighting its role in phage gene regulation.

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