Novel Variants of Streptococcus thermophilus Bacteriophages Are Indicative of Genetic Recombination among Phages from Different Bacterial Species.

Bacteriophages are the main cause of fermentation failures in dairy plants. The majority of phages can be divided into either - or -type phages and are additionally characterized by examining the V2 region of their antireceptors. We screened a large number of phages from the Chr. Hansen A/S collection, using PCR specific for the - or -type phages, 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 than the traditional phages. The third phage, CHPC1151, had a tail size similar to those of the - or -type phages, but it displayed a different baseplate structure. Sequencing analysis revealed the genetic similarity of CHPC577 and CHPC926 with a subgroup of P335 phages. Phage CHPC1151 was closely related to the atypical phage 5093, homologous with a nondairy streptococcal prophage. By testing adsorption of the related streptococcal and lactococcal phages to the surface of and strains, we revealed the possibility of cross-interactions. Our data indicated that the use of together with , extensively applied for dairy fermentations, triggered the recombination between phages infecting different bacterial species. A notable diversity among phage populations requires that a new classification of the group be proposed. 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.