Genomic organization and molecular characterization of SM1, a temperate bacteriophage of Streptococcus mitis

Area of Science:

• Microbiology
• Virology
• Genomics

Background:

• Streptococcus mitis binds to human platelets via proteins PblA and PblB.
• These proteins are encoded by a lysogenic bacteriophage, SM1, the first identified prophage in S. mitis.
• The potential role of phage-encoded proteins in bacterial virulence necessitates detailed characterization of SM1.

Purpose of the Study:

• To conduct a comprehensive characterization of the Streptococcus mitis bacteriophage SM1.
• To identify genes and potential functions of SM1 proteins, particularly those involved in virulence.
• To determine the phylogenetic relationship of SM1 to other bacteriophages.

Main Methods:

• Genome sequencing of the SM1 bacteriophage.
• Bioinformatic analyses, including BLAST searches for protein homology.
• N-terminal sequencing of SM1 proteins to assign putative functions.
• Examination of phage structural components.

Main Results:

• The SM1 genome is 34,692 bp with a 39% G+C content, containing 56 identified genes.
• SM1 genes exhibit a modular organization related to its life cycle.
• SM1 proteins show homology to proteins from various lambdoid phages.
• Putative functions were assigned to key proteins, including integrase, terminase, and major structural proteins.
• The major capsid protein may assemble phage heads similarly to phage r1t.

Conclusions:

• SM1 possesses genes potentially contributing to Streptococcus mitis virulence.
• SM1 shares characteristics with lambdoid phages, suggesting a role in phage evolution.
• SM1 represents a distinct subfamily within the Siphoviridae, including phages r1t and SF370.3.