Constitutive Activation of PrfA Tilts the Balance of Listeria monocytogenes Fitness Towards Life within the Host versus Environmental Survival

Abstract

PrfA is a key regulator of Listeria monocytogenes pathogenesis and induces the expression of multiple virulence factors within the infected host. PrfA is post-translationally regulated such that the protein becomes activated upon bacterial entry into the cell cytosol. The signal that triggers PrfA activation remains unknown, however mutations have been identified (prfA* mutations) that lock the protein into a high activity state. In this report we examine the consequences of constitutive PrfA activation on L. monocytogenes fitness both in vitro and in vivo. Whereas prfA* mutants were hyper-virulent during animal infection, the mutants were compromised for fitness in broth culture and under conditions of stress. Broth culture prfA*-associated fitness defects were alleviated when glycerol was provided as the principal carbon source; under these conditions prfA* mutants exhibited a competitive advantage over wild type strains. Glycerol and other three carbon sugars have been reported to serve as primary carbon sources for L. monocytogenes during cytosolic growth, thus prfA* mutants are metabolically-primed for replication within eukaryotic cells. These results indicate the critical need for environment-appropriate regulation of PrfA activity to enable L. monocytogenes to optimize bacterial fitness inside and outside of host cells.

Impact of glycerol-3-phosphate dehydrogenase on virulence factor production byPseudomonas aeruginosa

“…For example, catabolism of glycerol produces hydrogen peroxide in Mycoplasma pneumoniae, which is a major virulence factor for this bacterium (Hames et al 2009). In addition, growth on glycerol appears to enhance Listeria monocytogenes virulence (Bruno and Freitag 2010), and genes that encode for glycerol metabolism are upregulated in Legionella pneumophila (Faucher et al 2011) during infection. We show here that defects in glycerol metabolism affect the production of several virulence determinants by P. aeruginosa, presumably by rerouting carbon intermediates in central metabolism.…”

Characterization of the Intracellular Glutamate Decarboxylase System: Analysis of Its Function, Transcription, and Role in the Acid Resistance of Various Strains of Listeria monocytogenes

“…Therefore, this behavior that we previously observed in 10403S (12) is common between strains, and it is puzzling because GadT2D2 is the main contributor of acid resistance in this bacterium and yet the cells have to rely on preexisting levels of these proteins produced prior to the acid challenge. Maybe this is related to an attempt to strike a balance between stress resistance and virulence, as it is known that upregulation of acid or stress resistance mechanisms can impair virulence (3,(13)(14)(15)(16)(17). Furthermore, no transcriptional upregulation of the gad genes occurred in LO28, which could be due to the high transcription of gadT2D2 and gadD3 at basal levels (see Fig.…”

Perforin-2 Protects Host Cells and Mice by Restricting the Vacuole to Cytosol Transitioning of a Bacterial Pathogen

“…The major transcriptional regulator of virulence gene expression in L. monocytogenes, PrfA, is itself activated posttranslationally following infection (30). L. monocytogenes strains expressing constitutively active PrfA variants (encoded by prfA* alleles) are hypervirulent in both cell culture and animal infection models (21,31). Perforin-2 ϩ/ϩ and Perforin-2 Ϫ/Ϫ macrophages were infected with one such prfA* strain that expresses a PrfA containing a G145S mutation.…”