Abstract
Intracellular bacterial pathogens are metabolically adapted to grow within mammalian cells. While these adaptations are fundamental to the ability to cause disease, we know little about the relationship between the pathogen's metabolism and virulence. Here we used an integrative Metabolic Analysis Tool that combines transcriptome data with genome-scale metabolic models to define the metabolic requirements of Listeria monocytogenes during infection. Twelve metabolic pathways were identified as differentially active during L. monocytogenes growth in macrophage cells. Intracellular replication requires de novo synthesis of histidine, arginine, purine, and branch chain amino acids (BCAAs), as well as catabolism of L-rhamnose and glycerol. The importance of each metabolic pathway during infection was confirmed by generation of gene knockout mutants in the respective pathways. Next, we investigated the association of these metabolic requirements in the regulation of L. monocytogenes virulence. Here we show that limiting BCAA concentrations, primarily isoleucine, results in robust induction of the master virulence activator gene, prfA, and the PrfA-regulated genes. This response was specific and required the nutrient responsive regulator CodY, which is known to bind isoleucine. Further analysis demonstrated that CodY is involved in prfA regulation, playing a role in prfA activation under limiting conditions of BCAAs. This study evidences an additional regulatory mechanism underlying L. monocytogenes virulence, placing CodY at the crossroads of metabolism and virulence.
Highlights
Intracellular bacterial pathogens have developed sophisticated mechanisms to enter eukaryotic cells and replicate within them
In agreement with previous studies of metabolic pathways that contribute to L. monocytogenes growth during in vitro infection, we identified arginine biosynthesis, branched chain amino acids (BCAA) biosynthesis and glycerol utilization as pathways highly active during intracellular replication [10,11,16]
In this study we examined the metabolism of the human bacterial pathogen L. monocytogenes during infection using both a standard bioinformatics pathway enrichment analysis and an integrative computational analysis of transcriptome data using the integrative Metabolic Analysis Tool (iMAT) tool
Summary
Intracellular bacterial pathogens have developed sophisticated mechanisms to enter eukaryotic cells and replicate within them. These mechanisms involve bacterial proteins that overcome host defense strategies and barriers as well as nutritional limitations. Each intracellular niche presents unique nutritional challenges demanding that bacteria exhibit specific metabolic adaptations to proliferate successfully. Vacuolar pathogens, such as Legionella pneumophilla and Mycobacterium tuberculosis, actively modify their compartment via secretion of effector proteins that enrich the vacuole with nutrients to support growth; growth rate in the vacuole is much slower than in rich media. A better understanding of how these bacteria overcome nutritional limitations will give insight into cytosol nutrient composition and could facilitate development of drugs against intracellular pathogens
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