Identification of a Ligand on the Wip1 Bacteriophage Highly Specific for a Receptor on Bacillus anthracis

Abstract

bTectiviridae is a family of tailless bacteriophages with Gram-negative and Gram-positive hosts. The family model PRD1 and its close relatives all infect a broad range of enterobacteria by recognizing a plasmid-encoded conjugal transfer complex as a receptor. In contrast, tectiviruses with Gram-positive hosts are highly specific to only a few hosts within the same bacterial species. The cellular determinants that account for the observed specificity remain unknown. Here we present the genome sequence of Wip1, a tectivirus that infects the pathogen Bacillus anthracis. The Wip1 genome is related to other tectiviruses with Gram-positive hosts, notably, AP50, but displays some interesting differences in its genome organization. We identified Wip1 candidate genes for the viral spike complex, the structure located at the capsid vertices and involved in host receptor binding. Phage adsorption and inhibition tests were combined with immunofluorescence microscopy to show that the Wip1 gene product p23 is a receptor binding protein. His-p23 also formed a stable complex with p24, a Wip1 protein of unknown function, suggesting that the latter is involved with p23 in host cell recognition. The narrow host range of phage Wip1 and the identification of p23 as a receptor binding protein offer a new range of suitable tools for the rapid identification of B. anthracis.

Prevalence, Genetic Diversity, and Host Range of Tectiviruses among Members of the Bacillus cereus Group

“…Wip1 was not included in the alignments because its genome was not available at the time (25). On the basis of these whole-genome alignments, two variable regions were retained for the following reasons: (i) localization in different modules of the tectivirus genome (Fig.…”

“…Although the six fully sequenced tectivirus-like elements from the B. cereus group are also conserved, their pairwise nucleotide sequence identity appears to be more diverse, ranging from 23.5 to 100% (23,25). Moreover, genome alignments of this group of tectiviruses indicated the existence of two highly variable regions (HVRs).…”

“…Interestingly, phages in cluster MurB (i.e., AP50 and Wip1) are the only tectiviruses reported to infect B. anthracis (24,25,(50)(51)(52), whereas cluster MurA encompasses phages isolated from other members of the B. cereus group. Phages AP50 and Wip1 were isolated from soil and earthworm (Eisenia fetida) intestine samples, respectively, using B. anthracis Sterne as the host strain throughout the initial isolation and enrichment processes (51,53).…”

“…The PRD1-like phages infect Gramnegative enterobacteria such as Escherichia coli or Salmonella en-terica, while GIL01, Bam35, GIL16, AP50, and Wip1 are representatives of temperate tectiviruses preying on the B. cereus group (18,(21)(22)(23)(24)(25); A. Gillis and J. Mahillon, unpublished data). The second group of phages also exhibits strong similarity to the B. cereus linear plasmid pBClin15 (23,26).…”

Bam35 Tectivirus Intraviral Interaction Map Unveils New Function and Localization of Phage ORFan Proteins

“…Further, they are also closely related to the B. cereus linear plasmid pBClin15 (8). Interest in the study of tectiviruses of Gram-positive bacteria has increased in the last few years due to the narrow host specificity of some of them for dangerous human pathogens (10,11), their complex diversity and variability patterns (2,7), and their possible phylogenetic relationship with some groups of eukaryotic viruses and mobile elements (12,13). However, they remain less well-known than the PRD1-related bacteriophages.…”