Polyamines and linear DNA mediate bacterial threat assessment of bacteriophage infection.

Monitoring the extracellular environment for danger signals is a critical aspect of cellular survival. However, the danger signals released by dying bacteria and the mechanisms bacteria use for threat assessment remain largely unexplored. Here we show that lysis of cells releases polyamines that are subsequently taken up by surviving cells via a mechanism that relies on Gac/Rsm signaling. While intracellular polyamines spike in surviving cells, the duration of this spike varies according to the infection status of the cell. In bacteriophage-infected cells, intracellular polyamines are maintained at high levels, which inhibits replication of the bacteriophage genome. Many bacteriophages package linear DNA genomes and linear DNA is sufficient to trigger intracellular polyamine accumulation, suggesting that linear DNA is sensed as a second danger signal. Collectively, these results demonstrate how polyamines released by dying cells together with linear DNA allow to make threat assessments of cellular injury.