Abstract
BackgroundDespite continuous research efforts, bacterio(phages) infecting Lactococcus lactis starter strains persist as a major threat to dairy fermentations. The lactococcal P335 phages, which are currently classified into four sub-groups (I-IV), are the second most frequently isolated phage group in an industrial dairy context.ResultsThe current work describes the isolation and comparative genomic analysis of 17 novel P335 group phages. Detailed analysis of the genomic region of P335 phages encoding the so-called “baseplate”, which includes the receptor binding protein (RBP) was combined with a functional characterization of the RBP of sub-group III and IV phages. Additionally, calcium-dependence assays revealed a specific requirement for calcium by sub-group IV phages while host range analysis highlighted a higher number of strains with CWPS type A (11 of 39 strains) are infected by the P335 phages assessed in this study than those with a C (five strains), B (three of 39 strains) or unknown (one of 39 strains) CWPS type.ConclusionsThese analyses revealed significant divergence among RBP sequences, apparently reflecting their unique interactions with the host and particularly for strains with a type A CWPS. The implications of the genomic architecture of lactococcal P335 phages on serving as a general model for Siphoviridae phages are discussed.
Highlights
Despite continuous research efforts, bacterio(phages) infecting Lactococcus lactis starter strains persist as a major threat to dairy fermentations
Genomic and morphological analysis of the P335 phage isolates In this study, it was aimed to ascertain the genetic link to the morphological characteristics of P335 phages, in particular focusing on the tail tip region which is involved in interactions with the host
While overall nucleotide or proteomic content was widely applied to the classification of phages previously, morphological analysis combined with sequence relatedness of the genomic region encoding the so-called adhesion device was employed as the basis for the classification of these genetically and morphologically diverse phages in this study
Summary
Bacterio(phages) infecting Lactococcus lactis starter strains persist as a major threat to dairy fermentations. Comparative genomic analysis combined with morphological analysis was employed to classify the heterogenous P335 phages, resulting in the identification of four distinct subgroups, designated I – IV, based on distinct genetic lineages and morphological features. The latter features relate to their distal tail regions as follows: sub-group I consists of just a single representative phage, BK5-T, and is typified as possessing a long fibre at the tip of its tail; subgroup II phages, representatives of which include Tuc2009, TP901-1, P335 and ul, are endowed with a double-disc baseplate; while sub-groups III and IV represent genetically distinct phages that exhibit a small “stubby” distal tail structure
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