The mobility of packaged phage genome controls ejection dynamics.

Alex Evilevitch

doi:10.7554/elife.37345

Abstract

The cell decision between lytic and lysogenic infection is strongly influenced by dynamics of DNA injection into a cell from a phage population, as phages compete for limited resources and progeny. However, what controls the timing of viral DNA ejection events was not understood. This in vitro study reveals that DNA ejection dynamics for phages can be synchronized (occurring within seconds) or desynchronized (displaying minutes-long delays in initiation) based on mobility of encapsidated DNA, which in turn is regulated by environmental factors, such as temperature and extra-cellular ionic conditions. This mechano-regulation of ejection dynamics is suggested to influence viral replication where the cell's decision between lytic and latent infection is associated with synchronized or desynchronized delayed ejection events from phage population adsorbed to a cell. Our findings are of significant importance for understanding regulatory mechanisms of latency in phage and Herpesviruses, where encapsidated DNA undergoes a similar mechanical transition.

Highlights

Gaining insight into the dynamics of viral gene delivery into a host cell during infection is critical for understanding the virus replication dynamics (Ellis and Delbruck, 1939; You and Yin, 1999; Gallet et al, 2011; Lee et al, 1997) and viral fitness (Burch and Chao, 2000; Abedon and Culler, 2007)
light scattering analysis (LS) measurements, on the other hand, record a decrease in total scattering intensity, I(0), from a phage population. This decrease is associated with a change in DNA scattering density inside capsids, reflecting the number of DNA-filled phage particles remaining as ejection events occur
As observed in the figure, the overall time for the ejection process is much slower than the ejection time for DNA translocation from a single phage ( 10 s) (Grayson et al, 2007) because ejection events at these conditions occur in a stochastic manner (Freeman et al, 2016)

Summary

Introduction

Gaining insight into the dynamics of viral gene delivery into a host cell during infection is critical for understanding the virus replication dynamics (Ellis and Delbruck, 1939; You and Yin, 1999; Gallet et al, 2011; Lee et al, 1997) and viral fitness (Burch and Chao, 2000; Abedon and Culler, 2007). A central method for studying virus replication dynamics is the ‘one-step growth cycle’ method, which was developed for an ex vivo model of phage growth in E. coli by Ellis and Delbruck (Ellis and Delbruck, 1939). For accurate quantification of the infectious cycle rate, it is critical that the infection is synchronized so that cells are infected at the same time This is achieved by incubating bacterial culture with phage, diluting the solution after phage has adsorbed to cells so that no more adsorption occurs, and measuring virus growth at different time intervals using a plaque assay. The dynamics of the phage adsorption step has been investigated (Moldovan et al, 2007; Mackay and Bode, 1976), the dynamics of the initiation of phage injection is poorly understood even though it has critical importance for virus growth rate studies

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Conclusion