Evolved distal tail carbohydrate binding modules of Lactobacillus phage J‐1: a novel type of anti‐receptor widespread among lactic acid bacteria phages

Abstract

Bacteriophage replication requires specific host-recognition. Some siphophages harbour a large complex, the baseplate, at the tip of their non-contractile tail. This baseplate holds receptor binding proteins (RBPs) that can recognize the host cell-wall polysaccharide (CWPS) and specifically attach the phage to its host. While most phages possess a dedicated RBP, the phage J-1 that infects Lactobacillus casei seemed to lack one. It has been shown that the phage J-1 distal tail protein (Dit) plays a role in host recognition and that its sequence comprises two inserted modules compared with 'classical' Dits. The first insertion is similar to carbohydrate-binding modules (CBMs), whereas the second insertion remains undocumented. Here, we determined the structure of the second insertion and found it also similar to several CBMs. Expressed insertion CBM2, but not CBM1, binds to L. casei cells and neutralize phage attachment to the bacterial cell wall and the isolated and purified CWPS of L. casei BL23 prevents CBM2 attachment to the host. Electron microscopy single particle reconstruction of the J-1 virion baseplate revealed that CBM2 is projected at the periphery of Dit to optimally bind the CWPS receptor. Taken together, these results identify J-1 evolved Dit as the phage RBP.

Functional carbohydrate binding modules identified in evolved dits from siphophages infecting various Gram‐positive bacteria

“…). The structure closest to this insertion is the CBM2 module of Lactobacillus casei BL23 phage J‐1 evolved Dit, the first example of an evolved Dit reported in literature (Dieterle et al, ). Furthermore, we identified ~50 phages infecting Streptococcus thermophilus that possess a long Dit with a CBM insertion.…”

“…The Dit sequences were aligned and two types of Dit proteins (or Dits) were discerned based on size differences, termed here as ‘classical’ (~250–300 amino acids) and long (~500 amino acids) or ‘evolved’ Dit types (Dieterle et al, ; ) (Fig. ).…”

“…We already mentioned that Lactobacillus phages Dit‐associated CBM decorations were only recently shown to promote binding to the host (Dieterle et al, ; ). We wondered whether these Dit insertions found in Lactobacillus phages and now in members of the L. lactis 936 phage group are even more widespread.…”

“…In addition to their RBP, many members of the so‐called 936 group of bacteriophages harbor CBM‐encompassing ‘decorations’ on the Dit baseplate component. Dit decorations have largely been ignored to date, while such decorations on Lactobacillus phages were recently shown to promote binding to the host (Dieterle et al, ; ). These decorations are not specific to Lactobacillus or Lactococcus phages: our non‐exhaustive survey indicates that they are present, and even abundant, in Gram‐positive bacterial species, including Mycobacterium .…”

“…Recently, certain phages were shown to possess an additional carbohydrate binding module (CBM) in addition to the RBP (Dieterle et al, ; ; Legrand et al, ). In phage Tuc2009, another P335 lactococcal phage that resembles TP901‐1, such an additional CBM is present within the BppA accessory baseplate protein (Legrand et al, ).…”