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Characterization of Streptococcus thermophilus host range phage mutants

Martin Duplessis1, Céline M Lévesque, Sylvain Moineau

  • 1Département de Biochimie et de Microbiologie, Faculté des Sciences et de Génie, Groupe de Recherche en Ecologie Buccale (GREB), Faculté de Médecine Dentaire, Université Laval, Quebec City, Quebec, Canada G1K 7P4.

Applied and Environmental Microbiology
|April 7, 2006
PubMed

Insights

Investigating phage-host interactions in Streptococcus thermophilus revealed that specific phage genes, orf15, orf17, and orf18, are crucial. Mutations in these genes allow phages to infect resistant bacterial strains, highlighting key phage proteins in host interactions.

Area of Science:

  • Microbiology
  • Bacteriology
  • Virology

Background:

  • Bacteriophages are viruses that infect bacteria and play a significant role in microbial ecology.
  • Understanding phage-host interactions is crucial for applications in food safety and biotechnology, particularly with starter cultures like Streptococcus thermophilus.
  • Phage resistance in bacterial populations is a common challenge in industrial fermentation processes.

Purpose of the Study:

  • To identify the genetic basis of phage resistance and host range expansion in Streptococcus thermophilus.
  • To elucidate the specific phage genes and proteins involved in overcoming bacterial resistance.
  • To gain insights into the molecular mechanisms of phage-host interactions in S. thermophilus.

Main Methods:

  • Generation of phage-resistant Streptococcus thermophilus mutants using transposon mutagenesis (Tn917).
  • Isolation and characterization of host range mutant phages capable of infecting resistant strains.
  • Genetic analysis of phage mutants, including sequencing and identification of point mutations in specific genes (orf15, orf17, orf18).
  • Protein identification using N-terminal sequencing and mass spectrometry (MALDI-TOF).

Main Results:

  • Isolation of a phage-resistant Streptococcus thermophilus derivative (SMQ-301R).
  • Identification of four host range phage mutants with expanded infectivity.
  • Determination that point mutations in three phage genes (orf15, orf17, and orf18) confer the ability to infect resistant strains.
  • Confirmation that these three genes encode structural proteins involved in phage-host interactions.

Conclusions:

  • At least three phage structural proteins, encoded by orf15, orf17, and orf18, are directly involved in mediating phage-host interactions in Streptococcus thermophilus.
  • Mutations in these specific phage genes can lead to expanded host range, enabling phages to infect resistant bacterial strains.
  • This study provides a molecular basis for understanding phage resistance mechanisms and offers potential targets for phage engineering in S. thermophilus.

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