Active lysogeny is a newly described type of bacterium–phage interaction in which an integrated prophage serves as a regulatory switch that controls the expression of bacterial genes. The prophage is integrated within the open reading frame (or adjacent regulatory region) of a bacterial gene with a crucial function, thereby deactivating the expression of the gene. A precise excision of the prophage, which restores the disrupted gene, is induced under conditions that require the gene’s expression. We termed this novel phage behavior active lysogeny, as the prophage is highly active transcriptionally and genomically yet preserves the lysogenic mode.
We study the active lysogeny phenomenon in human bacterial pathogen Listeria monocytogenes, that harbors a prophage in its genome within comK gene. We have previously shown that during macrophage cells infection the prophage excises its genome leaving an intact comK gene that is necessary to facilitate bacterial phagosomal escape. Even though phage excision occurs, it does not lead to generation of progeny virions and bacterial lysis, suggesting that the prophage cooperates with it host to promote successful mammalian cells infection.
In attempt to better understand the bacterial – phage interaction during active lysogeny, we first characterized the phage under the three life cycles: lysogenic, lytic and active lysogeny. Using phage excision, replication and gene transcription analysis, we identified distinct phage behavior for each cycle, suggesting specific modes of regulation. The data also pointed phage factors that are differently controlled during active lysogeny, which are now targets for future studies.