SummaryThe intracellular metabolism of Listeria monocytogenes was studied by 13 C-isotopologue profiling using murine J774A.1 macrophages as host cells. Six hours after infection, bacteria were separated from the macrophages and hydrolyzed. Amino acids were converted into tert-butyl-dimethylsilyl derivatives and subjected to gas chromatography/mass spectrometry. When the macrophages were supplied with [U-

Listeria monocytogenes is able to efficiently utilize glycerol as a carbon source. In a defined minimal medium, the growth rate (during balanced growth) in the presence of glycerol is similar to that in the presence of glucose or cellobiose. Comparative transcriptome analyses of L. monocytogenes showed high-level transcriptional upregulation of the genes known to be involved in glycerol uptake and metabolism (glpFK and glpD) in the presence of glycerol (compared to that in the presence of glucose and/or cellobiose). Levels of expression of the genes encoding a second putative glycerol uptake facilitator (GlpF 2 ) and a second putative glycerol kinase (GlpK 2 ) were less enhanced under these conditions. GlpK 1 but not GlpK 2 was essential for glycerol catabolism in L. monocytogenes under extracellular conditions, while the loss of GlpK 1 affected replication in Caco-2 cells less than did the loss of GlpK 2 and GlpD. Additional genes whose transcription levels were higher in the presence of glycerol than in the presence of glucose and cellobiose included those for two dihydroxyacetone (Dha) kinases and many genes that are under carbon catabolite repression control. Transcriptional downregulation in the presence of glycerol (compared to those in the presence glucose and cellobiose) was observed for several genes and operons that are positively regulated by glucose, including genes involved in glycolysis, N metabolism, and the biosynthesis of branched-chain amino acids. The highest level of transcriptional upregulation was observed for all PrfA-dependent genes during early and late logarithmic growth in glycerol. Under these conditions, a low level of HPr-Ser-P and a high level of HPr-His-P were present in the cells, suggesting that all enzyme IIA (EIIA) (or EIIB) components of the phosphotransferase system (PTS) permeases expressed will be phosphorylated. These and other data suggest that the phosphorylation state of PTS permeases correlates with PrfA activity.Listeria monocytogenes is known as a facultative intracellular pathogen that can cause severe systemic infections in humans (for recent reviews, see references 15 and 47). This bacterial pathogen has therefore been extensively studied in the last decades preferentially with respect to its virulence genes and the encoded virulence factors. The virulence factors identified were shown to be involved mainly in the intracellular (cytosolic) growth cycle, and their genes were highly expressed under intracellular growth conditions (26). Most of the virulence genes are under the control of the transcription activator PrfA, whose expression is regulated at the transcriptional and the posttranscriptional levels (for recent reviews, see references 21 and 27). In addition, the activity of the PrfA protein is modulated by an as-yet-unknown factor(s) whose production appears to be linked to the metabolism of L. monocytogenes.

In this report we examine the PEP-dependent phosphotransferase systems (PTSs) of Listeria monocytogenes EGD-e, especially those involved in glucose and cellobiose transport. This L. monocytogenes strain possesses in total 86 pts genes, encoding 29 complete PTSs for the transport of carbohydrates and sugar alcohols, and several single PTS components, possibly supporting transport of these compounds. By a systematic deletion analysis we identified the major PTSs involved in glucose, mannose and cellobiose transport, when L. monocytogenes grows in a defined minimal medium in the presence of these carbohydrates.

The human pathogen L. monocytogenes is a facultatively intracellular bacterium that survives and replicates in the cytosol of many mammalian cells. The listerial metabolism, especially under intracellular conditions, is still poorly understood. Recent studies analyzed the carbon metabolism of L. monocytogenes by the 13 C isotopologue perturbation method in a defined minimal medium containing [U-13 C 6 ]glucose. It was shown that these bacteria produce oxaloacetate mainly by carboxylation of pyruvate due to an incomplete tricarboxylic acid cycle. Here, we report that a pycA insertion mutant defective in pyruvate carboxylase (PYC) still grows, albeit at a reduced rate, in brain heart infusion (BHI) medium but is unable to multiply in a defined minimal medium with glucose or glycerol as a carbon source. Aspartate and glutamate of the pycA mutant, in contrast to the wild-type strain, remain unlabeled when [U-13 C 6 ]glucose is added to BHI, indicating that the PYCcatalyzed carboxylation of pyruvate is the predominant reaction leading to oxaloacetate in L. monocytogenes. The pycA mutant is also unable to replicate in mammalian cells and exhibits high virulence attenuation in the mouse sepsis model.Listeria monocytogenes is a human pathogen that can cause systemic infections, especially in immunocompromised people, with symptoms such as septicemia, (encephalo)meningitis, placentitis, and stillbirth. These Gram-positive bacteria are able to enter the cytosol of many mammalian cells after being taken up via normal or induced phagocytosis by professional phagocytes, mainly macrophages and dendritic cells, and nonphagocytic cells, such as epithelial cells, fibroblasts, and endothelial cells (1,8,13). While the virulence genes and their regulation (4, 21), as well as the encoded virulence factors (20, 22), necessary for the various steps of the intracellular replication cycle of L. monocytogenes have been extensively studied in the past few decades, there is still little information concerning the metabolic capacities and the metabolic adaptation processes (10) that enable these bacteria to efficiently replicate in the cytosol of their host cells.The information on listerial metabolism obtained from the genome sequence (7) suggests that these heterotrophic bacteria are capable of utilizing a variety of carbohydrates as carbon sources, since a large number of genes encoding phosphoenolpyruvate (PEP)-phosphotransferase systems (PTS) were identified. Furthermore, all genes encoding the enzymes necessary for the catabolism of glycerol and dihydroxyacetone are present in the L. monocytogenes genome (7,11). This genomic information is in accord with data from previous and more recent physiological studies (11,17,24).Most genes encoding the enzymes for the major catabolic pathways, namely, glycolysis, the citrate cycle, and the pentose phosphate cycle, are present in L. monocytogenes. The citrate cycle, however, seems to be interrupted, since the genes encoding 2-oxoglutarate dehydrogenase have not been identified in all L. monoc...

BackgroundIn the environment as well as in the vertebrate intestine, Listeriae have access to complex carbohydrates like maltodextrins. Bacterial exploitation of such compounds requires specific uptake and utilization systems.Methodology/Principal FindingsWe could show that Listeria monocytogenes and other Listeria species contain genes/gene products with high homology to the maltodextrin ABC transporter and utilization system of B. subtilis. Mutant construction and growth tests revealed that the L. monocytogenes gene cluster was required for the efficient utilization of maltodextrins as well as maltose. The gene for the ATP binding protein of the transporter was located distant from the cluster. Transcription analyses demonstrated that the system was induced by maltose/maltodextrins and repressed by glucose. Its induction was dependent on a LacI type transcriptional regulator. Repression by glucose was independent of the catabolite control protein CcpA, but was relieved in a mutant defective for Hpr kinase/phosphorylase.Conclusions/SignificanceThe data obtained show that in L. monocytogenes the uptake of maltodextrin and, in contrast to B. subtilis, also maltose is exclusively mediated by an ABC transporter. Furthermore, the results suggest that glucose repression of the uptake system possibly is by inducer exclusion, a mechanism not described so far in this organism.