Bacterial pathogens often carry multiple prophages and other phage-derived elements within their genome, some of which can produce viral particles in response to stress. Listeria monocytogenes 10403S harbors two phage elements in its chromosome, both of which can trigger bacterial lysis under stress: an active prophage (ϕ10403S) that promotes the virulence of its host and can produce infective virions, and a locus encoding phage tail-like bacteriocins. Here, we show that the two phage elements are co-regulated, with the bacteriocin locus controlling the induction of the prophage and thus its activity as a virulence-associated molecular switch. More specifically, a metalloprotease encoded in the bacteriocin locus is upregulated in response to stress and acts as an anti-repressor for CI-like repressors encoded in each phage element. Our results provide molecular insight into the phenomenon of polylysogeny and its intricate adaptation to complex environments.
Summary
Some
Listeria monocytogenes
(
Lm
) strains harbor a prophage within the
comK
gene, which renders it inactive. During
Lm
infection of macrophage cells, the prophage turns into a molecular switch, promoting
comK
gene expression and therefore
Lm
intracellular growth. During this process, the prophage does not produce infective phages or cause bacterial lysis, suggesting it has acquired an adaptive behavior suited to the pathogenic lifestyle of its host. In this study, we demonstrate that this non-classical phage behavior, named active lysogeny, relies on a transcriptional response that is specific to the intracellular niche. While the prophage undergoes lytic induction, the process is arrested midway, preventing the transcription of the late genes. Further, we demonstrate key phage factors, such as LlgA transcription regulator and a DNA replicase, that support the phage adaptive behavior. This study provides molecular insights into the adaptation of phages to their pathogenic hosts, uncovering unusual cooperative interactions.
The nitrogen phosphotransferase system (PTS Ntr ) is a regulatory cascade present in many bacteria, where it controls different functions. This system is usually composed of three basic components: enzyme I Ntr (EI Ntr ), NPr, and EIIA Ntr (encoded by the ptsP, ptsO, and ptsN genes, respectively). In Legionella pneumophila, as well as in many other Legionella species, the EIIA Ntr component is missing. However, we found that deletion mutations in both ptsP and ptsO are partially attenuated for intracellular growth. Furthermore, these two PTS Ntr components were found to be required for maximal expression of effector-encoding genes regulated by the transcriptional activator PmrA. Genetic analyses which include the construction of single and double deletion mutants and overexpression of wild-type and mutated forms of EI Ntr , NPr, and PmrA indicated that the PTS Ntr components affect the expression of PmrA-regulated genes via PmrA and independently from PmrB and that EI Ntr and NPr are part of the same cascade and require their conserved histidine residues in order to function. Furthermore, expression of the Legionella micdadei EII Ntr component in L. pneumophila resulted in a reduction in the levels of expression of PmrAregulated genes which was completely dependent on the L. pneumophila PTS components and the L. micdadei EII Ntr conserved histidine residue. Moreover, reconstruction of the L. pneumophila PTS in vitro indicated that EI Ntr is phosphorylated by phosphoenolpyruvate (PEP) and transfers its phosphate to NPr. Our results demonstrate that the L. pneumophila incomplete PTS Ntr is functional and involved in the expression of effector-encoding genes regulated by PmrA.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.