Visualizing the Structural Changes of Bacteriophage Epsilon15 and Its Salmonella Host during Infection

Abstract

The efficient mechanism by which double stranded DNA bacteriophages deliver their chromosome across the outer membrane, cell wall, and inner membrane of Gram-negative bacteria remains obscure. Advances in single particle electron cryo-microscopy have recently revealed details of the organization of the DNA injection apparatus within the mature virion for various bacteriophages, including epsilon15 (ε15) and P-SSP7. We have used electron cryo-tomography and 3D subvolume averaging to capture snapshots of ε15 infecting its host Salmonella anatum. These structures suggest the following stages of infection. In the first stage, the tailspikes of ε15 attach to the surface of the host cell. Next ε15's tail hub attaches to a putative cell receptor and establishes a tunnel through which the injection core proteins behind the portal exit the virion. A tube spanning the periplasmic space is formed for viral DNA passage, presumably from the rearrangement of core proteins or from cellular components. This tube would direct the DNA into the cytoplasm and protect it from periplasmic nucleases. Once the DNA has been injected into the cell, the tube and portal seals, and the empty bacteriophage remains at the cell surface.

Structural remodeling of bacteriophage T4 and host membranes during infection initiation

“…Cryo-ET is being increasingly used to study phage-host interactions (47)(48)(49)(50)(51)(52). We recently developed skinny E. coli minicell as a host to study phage infection in situ (53,54).…”

Characterization of lytic Pseudomonas aeruginosa bacteriophages via biological properties and genomic sequences

“…4 Adsorption. Adsorption rate constants were 2.7×10 −8 and 3.0×10 −8 ml/min for vB_Pae-Kakheti25 and vB_Pae-TbilisiM32, respectively models of podoviral infection have assumed that the tail hub opens up to form a tube which becomes extended by internal virion proteins to allow passage of DNA to the cell (Chang et al 2010b). Others propose that the tail hub must be displaced to allow the internal virion proteins to form the injection tube .…”

Structure of the phage TP901-1 1.8 MDa baseplate suggests an alternative host adhesion mechanism

“…Binding of myophage T4 to the host lipopolysaccharides induces dramatic rearrangements of its tail extremity allowing irreversible commitment to the target cell followed by puncturing of its surface (3,5). The emerging picture for Podoviridae is that after attachment to the cell envelope, the minor phage proteins are ejected to form a tube across the periplasm thereby directing the viral DNA into the host cytoplasm (8). Siphophage p2, belonging to the 936-species of lactococcal phages, exhibits a Ca 2þ -mediated activation mechanism inducing a 200°rotation of the receptor-binding proteins (RBPs) to establish multiple interactions with host saccharides and initiate infection (7).…”