Identification of Host Genes That Influence the Bacteriophage Lambda (λ) T4 Exclusion (Rex) Phenotype.

The T4r exclusion (Rex) phenotype is the inability of T4 mutant bacteriophage to propagate in hosts () lysogenized by bacteriophage lambda (λ). The Rex phenotype, triggered by T4 infection of a λ lysogen, results in rapid membrane depolarization imposing a harsh cellular environment that resembles stationary phase. Rex "activation" has been proposed as an altruistic cell death system to protect the λ prophage and its host from T4r superinfection. Although well studied for over 60 years, the mechanism behind Rex still remains unclear. We have identified key nonessential genes involved in this enigmatic exclusion system by examining T4r infection across a collection of single-gene knockouts. We further developed a system for rapid, one-step isolation of host mutations that could attenuate/abrogate the Rex phenotype. For the first time, we identified host mutations that influence Rex activity and host sensitivity to T4 infection. Among others, notable genes include , , , , , , , , and They are critical players in cellular osmotic balance and are part of the stationary phase and/or membrane distress regulons. Based on these findings, we propose a new model that connects Rex to the σ, σ regulons and key membrane proteins.