Abstract
Bacteriophages use a large number of different bacterial cell envelope structures as receptors for surface attachment. As a consequence, bacterial surfaces represent a major control point for the defense against phage attack. One strategy for phage population control is the production of outer membrane vesicles (OMVs). In Gram-negative host bacteria, O-antigen-specific bacteriophages address lipopolysaccharide (LPS) to initiate infection, thus relying on an essential outer membrane glycan building block as receptor that is constantly present also in OMVs. In this work, we have analyzed interactions of Salmonella (S.) bacteriophage P22 with OMVs. For this, we isolated OMVs that were formed in large amounts during mechanical cell lysis of the P22 S. Typhimurium host. In vitro, these OMVs could efficiently reduce the number of infective phage particles. Fluorescence spectroscopy showed that upon interaction with OMVs, bacteriophage P22 released its DNA into the vesicle lumen. However, only about one third of the phage P22 particles actively ejected their genome. For the larger part, no genome release was observed, albeit the majority of phages in the system had lost infectivity towards their host. With OMVs, P22 ejected its DNA more rapidly and could release more DNA against elevated osmotic pressures compared to DNA release triggered with protein-free LPS aggregates. This emphasizes that OMV composition is a key feature for the regulation of infective bacteriophage particles in the system.
Highlights
Bacteriophages are ubiquitous in the microbial world and major players in many bacterial ecosystems
Either inner membrane (IM) and outer membrane (OM) were separated on sucrose density gradients or IMs were solubilized by detergents to collect the OM fraction by centrifugation (Thein et al, 2010)
We found that the plaque-forming units in the presence of membrane preparationderived outer membrane vesicles (OMVs) were reduced rapidly to less than 5% of the initial value (Figure 3)
Summary
Bacteriophages are ubiquitous in the microbial world and major players in many bacterial ecosystems They perform a variety of life styles, with prophages or mature phage particles as prominent examples of prevalent phage states (Feiner et al, 2015). Key event in a phage’s life cycle is the interaction with host surface receptors to initiate infection of the bacterial host. If this step is successful, the resulting genome transfer to the bacterial cytosol will open the route for a plethora of phage genome functions inside the host cell (Salmond and Fineran, 2015; Erez et al, 2017; Rostol and Marraffini, 2019). Bacteria constantly modify their surface composition to escape from phage attack (Rostol and Marraffini, 2019)
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