Metaviromes in whey samples produced over 12 years using TK5 starter culture

TK5 is a Cheddar starter culture containing mixed strains, and was exclusively applied to the Cheddar production over 12-year period (1982-1993) in a Danish dairy named “Øster Tørslev” (Nielsen 1998). By taking samples approx. twice a year, in total 22 whey samples were obtained during that period and have been stored frozen since arrival. To study the phage population, the bacteriophages in the 22 whey samples as well as 1 control (TK5 starter culture without having whey added) were amplified twice in the TK5 culture. Metaviromes from these 23 samples were analysed by metagenomic approach. The results showed that the whey metaviromes all contained sequences of lactococcal 936 phage species or the lactococcal P335 phage quasi-species (92-99 % of reads). Metavirome reads mapping to 1706 species were found in 3 of late-time whey samples (2,42-28,9%). Sequences mapping to Satellite species, KSY1 species, and 949 species were also found in low (<0.1 to 5 %) levels in some whey samples. Metaviromes from control samples were dominated by sequences mapping to the 936 phage species, indicating that the TK5 starter is phage carrying. RBP diversity results showed the RBP diversity of 936 species were regularly increasing by time, special in the late-time whey samples, indicating more 936 species phages were developed during the 12-year period.