P22 mediated recombination of frt-sites

Viral Transmission Dynamics at Single-Cell Resolution Reveal Transiently Immune Subpopulations Caused by a Carrier State Association

Monitoring the complex transmission dynamics of a bacterial virus (temperate phage P22) throughout a population of its host (Salmonella Typhimurium) at single cell resolution revealed the unexpected existence of a transiently immune subpopulation of host cells that emerged from peculiarities preceding the process of lysogenization. More specifically, an infection event ultimately leading to a lysogen first yielded a phage carrier cell harboring a polarly tethered P22 episome. Upon subsequent division, the daughter cell inheriting this episome became lysogenized by an integration event yielding a prophage, while the other daughter cell became P22-free. However, since the phage carrier cell was shown to overproduce immunity factors that are cytoplasmically inherited by the P22-free daughter cell and further passed down to its siblings, a transiently resistant subpopulation was generated that upon dilution of these immunity factors again became susceptible to P22 infection. The iterative emergence and infection of transiently resistant subpopulations suggests a new bet-hedging strategy by which viruses could manage to sustain both vertical and horizontal transmission routes throughout an infected population without compromising a stable co-existence with their host.

Extensive co-evolution with their host has shaped bacterial viruses into the most abundant and sophisticated pathogens known to date. However, how these important viral pathogens manage to safely exploit their host without jeopardizing stable co-existence remains a central question, since horizontal (lytic) transmission can reduce the number of susceptible host cells and cause pathogen extinction, while vertical (lysogenic) transmission impairs pathogen abundance. Scrutinizing transmission of temperate phage P22 throughout a bacterial population at single cell resolution now revealed that this phage is able to disseminate immunity factors that allow the emergence of transiently resistant subpopulations of host cells. The continued fostering and consumption of such subpopulations points to an entirely new strategy by which viruses could manage to sustain an active infection with their host.