Project Details
Projekt
Mechanisms of bacterial programmed cell death in phage defense: interplay of NAD+ depletion and the effector phospholipase PlaB
Applicant
Professorin Dr. Antje Flieger
Subject Area
Medical Microbiology and Mycology, Hygiene, Molecular Infection Biology
Term
since 2024
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 548567961
Legionella pneumophila (Lpn), an important intracellular bacterial pathogen, infects the human lung and environmental protozoa. It is well established that interaction with protozoa shaped its lifestyle and its virulence factor arsenal. Similarly, sharing of aqueous environments with bacteriophages might have led to acquisition of phage defence strategies which may also advance bacterial virulence. For example, the phospholipase A PlaB is critical for full virulence of Lpn and we here propose that it is moreover an efficient phage defense effector by executing cell death. Like eukaryotes, bacteria possess a variety of mechanisms, such as NAD+ depletion, to counteract viral infections but many details of phage defense are currently not understood. We recently uncovered the unusual mechanism which controls activity of PlaB by NAD+. Specifically, physiological concentrations of NAD+ stabilize inactive PlaB tetramers while low NAD+ results in dissociation into active PlaB dimers and unleashment of fierce phospholipase activity (Diwo et al.: https://doi.org/10.1073/pnas.201704611). Since NAD+ is usually confined to the intracellular milieu, we presumed an intrinsic function of PlaB in programmed bacterial cell death which is key to abortive phage infection (abi). Consistent with NAD+ being central for regulation of PlaB`s activity, our attention was caught by studying gene co-occurrences, which revealed conservation of plaB with NAD+ consuming enzyme genes, such as RES-Xre toxin antitoxin system genes, SIR2-, and TIR-domain-containing protein genes suggesting a functional link. Indeed, co-expression of PlaB with NAD+ consumers in E. coli and Lpn resulted in PlaB-dependent rapid cell death when NAD+ dropped to sub-physiological levels. To analyze PlaBs characteristics as a putative death effector and its interplay with NAD+ depletion in the context of phage infection, we propose to address the following research aims: we will study 1) the impact of NAD+ depletion and PlaB on host defense against phages, 2) determinants of PlaB action and localization and their importance in phage defense, and 3) new candidate effectors with similar NAD+ depletion-dependent activation like PlaB. In summary, this project will give an insight into important physiological interactions upon NAD+ depletion-dependent phage defense.
DFG Programme
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