Diversity and prevalence of dairy streptococcal phages in two European dairy fermentation facilities over a one-year period

Bacteriophages (or phages) represent a major challenge to industrial dairy fermentations and may cause reduced acidification of the milk substrate. Streptococcus thermophilus is a thermophilic lactic acid bacterium widely used in dairy fermentations. Here, we sought to establish the presence and diversity of phages present in two distinct factories employing the same dairy streptococcal starter cultures, employing a culture-based phage screening approach supplemented with culture-independent phageome analyses. It was established that cheese whey samples from one factory had a very low abundance/diversity of phages, while those of the second factory contained much higher levels and diversity of phages. In total, 41 phages were iso-lated, and among these were 34 Moineauvirus and 7 Vansinderenvirus members. Phylogenetic analysis of the deduced receptor-binding proteins of these phages established homogeneity among those of Vansinderenvirus and significant heterogeneity among Moineauvirus members. Furthermore, the receptor-binding protein phylogeny data combined with host range and geno-typing data indicate that the receptor for both Vansinderenvirus and Moineauvirus phages is a carbohydrate, which creates a roadmap for further investigation into the binding preferences of these industrially significant phages.