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Phage-host interactions in Streptococcus thermophilus: Genome analysis of phages isolated in Uruguay and ectopic

Rodrigo Achigar1, Alfonso H Magadán2, Denise M Tremblay2

  • 1Laboratorio de Microbiología Molecular, Departamento de Biociencias, Facultad de Química, Universidad de la República, Montevideo, Uruguay.

Scientific Reports
|March 7, 2017
PubMed

Insights

This study isolated Streptococcus thermophilus phages from failed mozzarella production. It found that these phages and bacterial CRISPR arrays are similar globally, and bacteria can acquire new spacers within CRISPR arrays.

Area of Science:

  • Microbiology
  • Bacteriology
  • Genomics

Background:

  • Streptococcus thermophilus is a key starter culture in dairy fermentation.
  • Bacteriophage infections can cause significant economic losses in the dairy industry.
  • Bacteriophage resistance in S. thermophilus is often mediated by CRISPR-Cas systems.

Purpose of the Study:

  • To isolate and characterize virulent Streptococcus thermophilus phages from failed mozzarella production.
  • To analyze the CRISPR arrays of Uruguayan S. thermophilus strains and their spontaneous phage-insensitive mutants (BIMs).
  • To investigate the mechanism of spacer acquisition in CRISPR arrays.

Main Methods:

  • Isolation and characterization of cos-type virulent Streptococcus thermophilus phages.
  • Genome analysis of isolated phages.
  • Characterization of CRISPR1 and CRISPR3 arrays in S. thermophilus strains and BIMs.
  • Analysis of spontaneous bacteriophage-insensitive mutants (BIMs).

Main Results:

  • Three virulent S. thermophilus phages were isolated from failed mozzarella production.
  • Phages and CRISPR arrays showed similarities to global isolates and model strains.
  • All 23 analyzed BIMs acquired at least one new spacer in their CRISPR1 array.
  • Ectopic spacer acquisition was observed, with some mutants acquiring spacers within the array, potentially due to a leader sequence deletion.

Conclusions:

  • Natural S. thermophilus strains can acquire spacers ectopically within CRISPR arrays.
  • The findings contribute to understanding phage-bacterial interactions and CRISPR-Cas system mechanisms in dairy starter cultures.
  • This research has implications for preventing phage contamination and ensuring starter culture stability in the dairy industry.

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