Abstract
Myoviruses, bacteriophages with T4-like architecture, must contract their tails prior to DNA release. However, quantitative kinetic data on myovirus particle opening are lacking, although they are promising tools in bacteriophage-based antimicrobial strategies directed against Gram-negative hosts. For the first time, we show time-resolved DNA ejection from a bacteriophage with a contractile tail, the multi-O-antigen-specific Salmonella myovirus Det7. DNA release from Det7 was triggered by lipopolysaccharide (LPS) O-antigen receptors and notably slower than in noncontractile-tailed siphoviruses. Det7 showed two individual kinetic steps for tail contraction and particle opening. Our in vitro studies showed that highly specialized tailspike proteins (TSPs) are necessary to attach the particle to LPS. A P22-like TSP confers specificity for the Salmonella Typhimurium O-antigen. Moreover, crystal structure analysis at 1.63 Å resolution confirmed that Det7 recognized the Salmonella Anatum O-antigen via an ϵ15-like TSP, DettilonTSP. DNA ejection triggered by LPS from either host showed similar velocities, so particle opening is thus a process independent of O-antigen composition and the recognizing TSP. In Det7, at permissive temperatures TSPs mediate O-antigen cleavage and couple cell surface binding with DNA ejection, but no irreversible adsorption occurred at low temperatures. This finding was in contrast to short-tailed Salmonella podoviruses, illustrating that tailed phages use common particle-opening mechanisms but have specialized into different infection niches.
Highlights
Myoviruses, bacteriophages with T4-like architecture, must contract their tails prior to DNA release
For the first time in a bacteriophage with a contractile tail machine, we show the kinetics of this process that has so far neither been quantified for T4 nor for any other myovirus
In contrast to the typical, single-step DNA ejection mechanism found in noncontractile-tailed phages, we describe an additional kinetic step for genome release in the myovirus Det7, associated with its contractile tail machine
Summary
In Det, at permissive temperatures TSPs mediate O-antigen cleavage and couple cell surface binding with DNA ejection, but no irreversible adsorption occurred at low temperatures This finding was in contrast to short-tailed Salmonella podoviruses, illustrating that tailed phages use common particle-opening mechanisms but have specialized into different infection niches. Tailed dsDNA bacteriophages constitute one of the largest phage groups described so far [1] These viral particles are assemblies of icosahedral capsids containing the genome, a portal complex and a tail machine that provides effective means for host cell surface recognition and subsequent DNA transmission into the cytosol, thereby overcoming all bacterial outer protective layers. In vitro studies with noncontractile-tailed bacteriophages have shown that contact with isolated protein or LPS membrane receptors is sufficient to initiate conformational changes in the tail apparatus and in the portal complex leading to opening of the phage particle and release of its DNA contents (20, 26 –28). In contrast to the typical, single-step DNA ejection mechanism found in noncontractile-tailed phages, we describe an additional kinetic step for genome release in the myovirus Det, associated with its contractile tail machine
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