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A homolog of CcpA mediates catabolite control in Listeria monocytogenes but not carbon source regulation of virulence genes.

ABSTRACT: Readily utilizable sugars down-regulate virulence gene expression in Listeria monocytogenes, which has led to the proposal that this regulation may be an aspect of global catabolite regulation (CR). We recently demonstrated that the metabolic enzyme alpha-glucosidase is under CR in L. monocytogenes. Here, we report the cloning and characterization from L. monocytogenes of an apparent ortholog of ccpA, which encodes an important mediator of CR in several low-G+C-content gram-positive bacteria. L. monocytogenes ccpA (ccpALm) is predicted to encode a 335-amino-acid protein with nearly 65% identity to the gene product of Bacillus subtilis ccpA (ccpABs). Southern blot analysis with a probe derived from ccpALm revealed a single strongly hybridizing band and also a second band of much lower intensity, suggesting that there may be other closely related sequences in the L. monocytogenes chromosome, as is the case in B. subtilis. Disruption of ccpALm resulted in the inability of the mutant to grow on glucose-containing minimal medium or increase its growth rate in the presence of preferred sugars, and it completely eliminated CR of alpha-glucosidase activity in liquid medium. However, alpha-glucosidase activity was only partially relieved from CR on solid medium. These results suggest that ccpA is an important element of carbon source regulation in L. monocytogenes. Nevertheless, utilizable sugars still down-regulate the expression of hly, which encodes the virulence factor hemolysin, in a ccpALm mutant, indicating that CcpA is not involved in carbon source regulation of virulence genes.

SUBMITTER: Behari J

PROVIDER: S-EPMC107718 | biostudies-literature | 1998 Dec

REPOSITORIES: biostudies-literature

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A homolog of CcpA mediates catabolite control in Listeria monocytogenes but not carbon source regulation of virulence genes.

Behari J J Youngman P P

Journal of bacteriology 19981201 23

Readily utilizable sugars down-regulate virulence gene expression in Listeria monocytogenes, which has led to the proposal that this regulation may be an aspect of global catabolite regulation (CR). We recently demonstrated that the metabolic enzyme alpha-glucosidase is under CR in L. monocytogenes. Here, we report the cloning and characterization from L. monocytogenes of an apparent ortholog of ccpA, which encodes an important mediator of CR in several low-G+C-content gram-positive bacteria. L. ...[more]

PMID: 9829942

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Project description:The beta-glucoside cellobiose has been reported to specifically repress the PrfA-dependent virulence genes hly and plcA in Listeria monocytogenes NCTC 7973. This led to the hypothesis that beta-glucosides, sugars of plant origin, may act as signal molecules, preventing the expression of virulence genes if L. monocytogenes is living in its natural habitat (soil). In three other laboratory strains (EGD, L028, and 10403S), however, the effect of cellobiose was not unique, and all fermentable carbohydrates repressed hly. This suggested that the downregulation of virulence genes by beta-glucosides is not a specific phenomenon but, rather, an aspect of a global regulatory mechanism of catabolite repression (CR). We assessed the effect of carbohydrates on virulence gene expression in a panel of wild-type isolates of L. monocytogenes by using the PrfA-dependent phospholipase C gene plcB as a reporter. Utilization of any fermentable sugar caused plcB repression in wild-type L. monocytogenes. However, an EGD variant was identified in which, as in NCTC 7973, plcB was only repressed by beta-glucosides. Thus, the regulation of L. monocytogenes virulence genes by sugars appears to be mediated by two separate mechanisms, one presumably involving a CR pathway and another specifically responding to beta-glucosides. We have identified in L. monocytogenes a 4-kb operon, bvrABC, encoding an antiterminator of the BglG family (bvrA), a beta-glucoside-specific enzyme II permease component of the phosphoenolpyruvate-sugar phosphotransferase system (bvrB), and a putative ADP-ribosylglycohydrolase (bvrC). Low-stringency Southern blots showed that this locus is absent from other Listeria spp. Transcription of bvrB was induced by cellobiose and salicin but not by arbutin. Disruption of the bvr operon by replacing part of bvrAB with an interposon abolished the repression by cellobiose and salicin but not that by arbutin. Our data indicate that the bvr locus encodes a beta-glucoside-specific sensor that mediates virulence gene repression upon detection of cellobiose and salicin. Bvr is the first sensory system found in L. monocytogenes that is involved in environmental regulation of virulence genes.

Project description:A combination of phenotype microarrays, targeted stress resistance and virulence assays and comparative genome analysis was used to compare a set of Listeria monocytogenes strains including those involved in previous Swiss foodborne listeriosis outbreaks. Despite being highly syntenic in gene content these strains showed significant phenotypic variation in utilization of different carbon (C)-sources as well as in resistance of osmotic and pH stress conditions that are relevant to host and food associated environments. An outbreak strain from the 2005 Swiss Tomme cheese listeriosis outbreak (Lm3163) showed the highest versatility in C-sources utilized whereas the strain responsible for the 1983 to 1987 Vacherin Montd'or cheese listeriosis outbreak (LL195) showed the highest tolerance to both osmotic and pH stress conditions among the examined strains. Inclusion of L-norvaline led to enhanced resistance of acidic stress in all the examined strains and there were strain-strain-specific differences observed in the ability of other amino acids and urea to enhance acid stress resistance in L. monocytogenes. A strain dependent inhibition pattern was also observed upon inclusion of β-phenylethylamine under alkaline stress conditions. In targeted phenotypic analysis the strain-specific differences in salt stress tolerance uncovered in phenotypic microarrays were corroborated and variations in host cell invasion and virulence among the examined strains were also revealed. Outbreak associated strains representing lineage I serotype 4b showed superior pathogenicity in a zebrafish infection model whilst Lm3163 a lineage II serotype 1/2a outbreak strain demonstrated the highest cellular invasion capacity amongst the tested strains. A genome wide sequence comparison of the strains only revealed few genetic differences between the strains suggesting that variations in gene regulation and expression are largely responsible for the phenotypic differences revealed among the examined strains. Our results have generated data that provides a potential basis for the future design of improved Listeria specific media to enhance routine detection and isolation of this pathogen as well as provide knowledge for developing novel methods for its control in food.

Dataset Information

A homolog of CcpA mediates catabolite control in Listeria monocytogenes but not carbon source regulation of virulence genes.

Publications

A homolog of CcpA mediates catabolite control in Listeria monocytogenes but not carbon source regulation of virulence genes.

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