Discovery of phage determinants that confer sensitivity to bacterial immune systems

Over the past few years, numerous anti-phage defense systems have been discovered in bacteria. Although the mechanism of defense for some of these systems is understood, a major unanswered question is how these systems sense phage infection. To systematically address this question, we isolated 177 phage mu-tants that escape 15 different defense systems. In many cases, these escaper phages were mutated in the gene sensed by the defense system, enabling us to map the phage determinants that confer sensitivity to bacterial immunity. Our data identify specificity determinants of diverse retron systems and reveal phage-encoded triggers for multiple abortive infection systems. We find general themes in phage sensing and demonstrate that mechanistically diverse systems have converged to sense either the core replication ma-chinery of the phage, phage structural components, or host takeover mechanisms. Combining our data with previous findings, we formulate key principles on how bacterial immune systems sense phage invaders.

Automated summary

In recent years, various defense systems against phages have been found in bacteria. However, the mechanism of how these systems sense phage infection remains unknown. To address this question, the researchers isolated 177 phage mutants that can evade 15 different defense systems. These mutants were found to have mutations in the gene sensed by the defense system, providing insights into the determinants of phage sensitivity. The study identifies specific determinants of different retron systems and reveals phage-encoded triggers for abortive infection systems, shedding light on how bacterial immune systems sense phage invaders.