Abstract
Siphoviridae of the lactococcal 936 group are the most commonly encountered bacteriophages in the dairy processing environment. The 936 group phages possess a discrete baseplate at the tip of their tail—a complex harbouring the Receptor Binding Protein (RBP) which is responsible for host recognition and attachment. The baseplate-encoding region is highly conserved amongst 936 phages, with 112 of 115 publicly available phages exhibiting complete synteny. Here, we detail the three exceptions (Phi4.2, Phi4R15L, and Phi4R16L), which differ from this genomic architecture in possessing an apparent second RBP-encoding gene upstream of the “classical” rbp gene. The newly identified RBP possesses an elongated neck region relative to currently defined 936 phage RBPs and is genetically distinct from defined 936 group RBPs. Through detailed characterisation of the representative phage Phi4.2 using a wide range of complementary techniques, we demonstrated that the above-mentioned three phages possess a complex and atypical baseplate structure. Furthermore, the presence of both RBPs in the tail tip of the mature virion was confirmed, while the anticipated host-binding capabilities of both proteins were also verified.
Highlights
Owing to the potentially adverse economic impact phages have on commercial food fermentations, phages of lactic acid bacteria have become one of the most intensely studied groups of viruses [1].Phages of Lactococcus lactis can be divided into ten groups, incorporating members of both the Podoviridae and Siphoviridae families [2]
Analysis of deduced amino acid sequences suggests that the second second putative Receptor Binding Protein (RBP) gene, rbp2, encodes a typical 936 group RBP, which displays a high degree of putative RBP gene, rbp2, encodes a typical 936 group RBP, which displays a high degree of homology homology to the entire sequence of the RBP of p2 (Figure 2C)
Through detailed characterisation of Phi4.2, the phage for this dual-RBP phenomenon, it was revealed that these exceptions possess a number of representative phage for this dual-RBP phenomenon, it was revealed that these exceptions possess a significant differences to the typical 936 phage structure
Summary
Owing to the potentially adverse economic impact phages have on commercial food fermentations, phages of lactic acid bacteria have become one of the most intensely studied groups of viruses [1]. Phages of Lactococcus lactis can be divided into ten groups, incorporating members of both the Podoviridae and Siphoviridae families [2]. The 936 group phages appear to be the most prevalent [3] with 115 full genome sequences of 936 phages available as of January 2018 [4]. The 936 phages follow a strictly lytic lifestyle and possess a double-stranded DNA. Viruses 2018, 10, 668 genome encapsulated in an isometric capsid (45–60 nm). They exhibit a long, non-contractile tail of 130–165 nm in length [5]
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