Molecular ecology of Streptococcus thermophilus bacteriophage infections in a cheese factory

Abstract

A mozzarella cheese factory using an undefined, milk-derived Streptococcus thermophilus starter system was monitored longitudinally for 2 years to determine whether the diversity of the resident bacteriophage population arose from environmental sources or from genetic changes in the resident phage in the factory. The two hypotheses led to different predictions about the genetic diversity of the phages. With respect to host range, 12 distinct phage types were observed. With two exceptions, phages belonging to different lytic groups showed clearly distinct restriction patterns and multiple isolates of phages showing the same host range exhibited identical or highly related restriction patterns. Sequencing studies in a conserved region of the phage genome revealed no point mutations in multiple isolates of the same phage type, while up to 12% nucleotide sequence diversity was observed between the different phage types. This diversity is as large as that between the most different sequences from phages in our collection. These observations make unlikely a model that postulates a single phage invasion event and diversification of the phage during its residence in the factory. In the second stage of our factory study, a defined starter system was introduced that could not propagate the resident factory phage population. Within a week, three new phage types were observed in the factory while the resident phage population was decreased but not eliminated. Raw milk was the most likely source of these new phages, as phages with identical host ranges and restriction patterns were isolated from raw milk delivered to the factory during the intervention trial. Apparently, all of the genetic diversity observed in the S. thermophilus phages isolated during our survey was already created in their natural environment. A better understanding of the raw-milk ecology of S. thermophilus phages is thus essential for successful practical phage control.

Diversity among Lactobacillus paracasei phages isolated from a probiotic dairy product plant

“…Bacteriophage attacks against starters of lactic acid bacteria represent one of the major risks of acidifying delays, causing technological difficulties and economic losses (Jarvis 1989;Brüssow et al 1994;Bruttin et al 1997;Moineau and Lévesque 2005). Even though probiotic bacteria are mainly included in fermented dairy products as additives (usually as frozen and ⁄ or lyophilized powders) once the main fermentation process is finished, they can also be propagated during this stage, therefore acting as a starter (Watanabe et al 1970;Forsman et al 1993;Saarela et al 2000;Capra et al 2006b).…”

“…Although the dairy industry has accumulated substantial knowledge in the field of phage factory ecology, these data are generally not published. Some authors (Moineau et al 1996;Deveau et al 2006;Szczepań ska et al 2007) have investigated lactococcal phage diversity and not many studies have been performed to elucidate the origin of Streptococcus thermophilus phages in dairy environments (Brüssow et al 1994(Brüssow et al , 1998Bruttin et al 1997;Brüssow and Desiere 2001), despite these latter lactic acid bacteria are widely used as starters.…”

Comparison of the Lysogeny Modules from the TemperateStreptococcus thermophilusBacteriophages TP-J34 and Sfi21: Implications for the Modular Theory of Phage Evolution

“…We decided to address some questions of phage evolution and phage population biology with phages from Streptococcus thermophilus, a Gram-positive bacterium (Mercenier, 1990) used industrially in milk fermentation (lactic acid bacterium). Several phage collections are available for this phage family (Benbadis et al, 1990;Bru Èssow et al, 1994a;Fayard et al, 1993;Larbi et al, 1992;Le Marrec et al, 1997;Neve et al, 1989;Prevots et al, 1989) and the ecology of phage infections has been studied (Bruttin et al, 1997a). Finally, a molecular characterization of the temperate S. thermophilus phage Sfi21 was started (Bru Èssow et al, 1994b;Bru Èssow and Bruttin, 1995;Bruttin and Bru Èssow, 1996;Bruttin et al, 1997b,c;Desiere et al, 1997Desiere et al, , 1998, making this phage system an acceptable subject for the study of phage evolution.…”

Comparative Genomics of Streptococcus thermophilus Phage Species Supports a Modular Evolution Theory

“…Due to their industrial importance in milk fermentation (36), many S. thermophilus phages have been isolated, covering a substantial geographical diversity (reference 7 and references therein). A longitudinal factory survey has documented the ecological dynamics of phage infection (11). All phages characterized so far belong to the same morphological class (Siphoviridae, B1 morphotype) and the same DNA homology group (8,9), but they could be split into two groups: cos-site and pac-site phages.…”