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Novel variants of Streptococcus thermophilus bacteriophages indicate genetic recombination across phages from different bacterial species.

Research paper by Paula P Szymczak, Thomas T Janzen, Ana Rute AR Neves, Witold W Kot, Lars H LH Hansen, René R Lametsch, Horst H Neve, Charles M A P CM Franz, Finn K FK Vogensen

Indexed on: 01 Jan '17Published on: 01 Jan '17Published in: Applied and environmental microbiology



Abstract

Bacteriophages are the main cause of fermentation failures in dairy plants. The majority of Streptococcus thermophilus phages can be divided into either cos- or pac-type-phages and additionally characterized by examining the V2 region of their antireceptor. We screened a large number of S. thermophilus phages from the Chr. Hansen A/S collection, using PCR specific for the cos/pac-type, as well as for the V2 antireceptor region. Three phages did not produce positive results with the assays. Analysis of phage morphologies indicated that two of these phages, CHPC577 and CHPC926, had shorter tails compared to the traditional S. thermophilus phages. The third one, CHPC1151, had a tail size similar to the cos/pac-type phages, but it displayed a different baseplate structure. Sequencing analysis revealed genetic similarity of CHPC577 and CHPC926 with a subgroup of Lactococcus lactis P335 phages. Phage CHPC1151 was closely related to the atypical S. thermophilus phage 5093, homologous with a non-dairy streptococcal prophage. By testing adsorption of the related streptococcal and lactococcal phages to the surface of S. thermophilus and L. lactis strains, we revealed the possibility of cross-interactions. Our data indicated that the use of S. thermophilus together with L. lactis, extensively applied for dairy fermentations, triggered the recombination between phages infecting different bacterial species. A notable diversity among S. thermophilus phage populations requires that a new classification of the group be proposed.Streptococcus thermophilus is a component of thermophilic starter cultures commonly used for cheese and yogurt production. Characterizing streptococcal phages, understanding their genetic relationships, and studying their interactions with various hosts are the necessary steps for preventing and controlling phage attacks that occur during dairy fermentations.