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Glucose-1-phosphate utilization by Listeria monocytogenes is PrfA dependent and coordinately expressed with virulence
1Unidad de Microbiología e Immunología, Facultad de Veterinaria, Universidad Complutense, Madrid, Spain.
Abstract:
Virulence genes of the facultative intracellular pathogen Listeria monocytogenes are coordinately regulated by the activator protein PrfA, encoded by prfA, a member of the cyclic AMP receptor protein family of bacterial transcription factors. We found that prfA* mutants that constitutively overexpress the virulence regulon due to a Gly145Ser substitution in PrfA (M.-T. Ripio, G. Domínguez-Bernal, M. Lara, M. Suárez, and J.-A. Vázquez-Boland, J. Bacteriol. 179:1533-1540, 1997) rapidly utilized glucose-1-phosphate (G-1-P) as a carbon source for growth, in contrast to wild-type strains, which characteristically do not. Wild-type strains acquired the capacity for readily metabolizing G-1-P upon exposure to environmental conditions that activate the expression of prfA and PrfA-dependent virulence genes (i.e., culture at 37 degrees C in charcoal-treated medium). In these strains, G-1-P utilization followed an expressional pattern identical to that of virulence genes controlled by PrfA, with repression at 20 degrees C. Tn917 insertions in L. monocytogenes mutants selected for G-1-P utilization deficiency mapped to the plcA-prfA operon, a deltaprfA strain was totally unable to utilize G-1-P, and trans complementation with prfA constructs restored the ability to efficiently metabolize and grow on G-1-P to these mutants. Thus, G-1-P utilization by L. monocytogenes is under the tight positive control of the central virulence regulator, PrfA, and is coexpressed with PrfA-dependent pathogenicity determinants. It was recently reported that readily utilized carbohydrates, such as glucose or cellobiose, repress virulence genes in L. monocytogenes. We confirmed this but, interestingly, found that G-1-P does not inhibit expression of the PrfA regulon, indicating that this sugar follows a catabolic pathway that bypasses the repressor mechanism triggered by other readily metabolized carbon sources. PrfA dependence and coexpression with virulence genes suggest that utilization of exogenous G-1-P may be relevant to Listeria pathogenesis. G-1-P is the precursor metabolite and primary degradation product of glycogen and is therefore available within the mammalian cell. Based on our results, we hypothesize that G-1-P could play an important role as a growth substrate for intracellular Listeria.
Insights
Listeria monocytogenes utilizes glucose-1-phosphate (G-1-P) for growth, regulated by the virulence activator protein PrfA. This sugar metabolism bypasses typical carbohydrate repression, suggesting a role in Listeria pathogenesis within host cells.
Area of Science:
- Microbiology
- Bacterial Pathogenesis
- Molecular Biology
Background:
- Listeria monocytogenes virulence is controlled by the transcriptional activator protein PrfA.
- Virulence gene expression is typically repressed by readily metabolized carbohydrates.
- The carbon source utilization of L. monocytogenes is not fully understood.
Purpose of the Study:
- To investigate the regulation of glucose-1-phosphate (G-1-P) utilization in L. monocytogenes.
- To determine the relationship between G-1-P metabolism and virulence gene expression.
- To explore the potential role of G-1-P in Listeria pathogenesis.
Main Methods:
- Comparative growth studies of wild-type and mutant L. monocytogenes strains on G-1-P.
- Analysis of G-1-P utilization under different temperature conditions.
- Genetic analysis using Tn917 mutagenesis and complementation studies to identify regulatory genes.
- Assessment of PrfA regulon expression in the presence of G-1-P.
Main Results:
- Constitutive PrfA mutants (prfA*) readily utilized G-1-P, unlike wild-type strains.
- Wild-type strains gained G-1-P utilization capacity at 37°C, mirroring PrfA-dependent virulence gene expression.
- G-1-P utilization was dependent on the plcA-prfA operon and the PrfA protein.
- G-1-P did not repress PrfA-controlled virulence gene expression, unlike other sugars.
Conclusions:
- G-1-P utilization in L. monocytogenes is positively regulated by the virulence factor PrfA.
- G-1-P metabolism is co-expressed with virulence genes and bypasses carbohydrate-mediated repression.
- G-1-P, a glycogen metabolite found in host cells, may serve as a crucial growth substrate for intracellular Listeria.