Classification of Lytic Bacteriophages Attacking Dairy Leuconostoc Starter Strains

Abstract

ABSTRACTA set of 83 lytic dairy bacteriophages (phages) infecting flavor-producing mesophilic starter strains of theLeuconostocgenus was characterized, and the first in-depth taxonomic scheme was established for this phage group. Phages were obtained from different sources, i.e., from dairy samples originating from 11 German dairies (50Leuconostoc pseudomesenteroides[Ln. pseudomesenteroides] phages, 4Ln. mesenteroidesphages) and from 3 external phage collections (17Ln. pseudomesenteroidesphages, 12Ln. mesenteroidesphages). All phages belonged to theSiphoviridaefamily of phages with isometric heads (diameter, 55 nm) and noncontractile tails (length, 140 nm). With the exception of one phage (i.e., phage ΦLN25), allLn. mesenteroidesphages lysed the same host strains and revealed characteristic globular baseplate appendages. Phage ΦLN25, with different Y-shaped appendages, had a unique host range. Apart from two phages (i.e., phages P792 and P793), allLn. pseudomesenteroidesphages shared the same host range and had plain baseplates without distinguishable appendages. They were further characterized by the presence or absence of a collar below the phage head or by unique tails with straight striations. Phages P792 and P793 with characteristic fluffy baseplate appendages could propagate only on other specific hosts. AllLn. mesenteroidesand allLn. pseudomesenteroidesphages were members of two (host species-specific) distinct genotypes but shared a limited conserved DNA region specifying their structural genes. A PCR detection system was established and was shown to be reliable for the detection of allLeuconostocphage types.