Bacteriophage-host interactions in Streptococcus thermophilus and their impact on co-evolutionary processes.

Bacteriophages (or phages) represent a persistent threat to the success and reliability of food fermentation processes. Recent reports of phages that infect Streptococcus thermophilus have highlighted the diversification of phages of this species. Phages of S. thermophilus typically exhibit a narrow range, a feature that is suggestive of diverse receptor moieties being presented on the cell surface of the host. Cell wall polysaccharides including rhamnose-glucose polysaccharides (RGP) and exopolysaccharides (EPS) have been implicated as being involved in the initial interactions with several phages of this species. Following internalisation of the phage genome, the host presents several defences including CRISPR-Cas and restriction and modification systems to limit phage proliferation. This review provides a current and holistic view of the interactions of phages and their S. thermophilus host cells and how this has influenced the diversity and evolution of both entities.