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Global Transcriptional Response of Three Highly Acid-Tolerant Field Strains of Listeria monocytogenes to HCl Stress

Authors
  • Horlbog, Jule Anna
  • Stevens, Marc J. A.
  • Stephan, Roger
  • Guldimann, Claudia
Type
Published Article
Journal
Microorganisms
Publisher
MDPI AG
Publication Date
Oct 16, 2019
Volume
7
Issue
10
Identifiers
DOI: 10.3390/microorganisms7100455
PMID: 31623206
PMCID: PMC6843411
Source
PubMed Central
Keywords
License
Green

Abstract

Tolerance to acid is of dual importance for the food-borne pathogen Listeria monocytogenes : acids are used as a preservative, and gastric acid is one of the first defenses within the host. There are considerable differences in the acid tolerance of strains. Here we present the transcriptomic response of acid-tolerant field strains of L. monocytogenes to HCl at pH 3.0. RNAseq revealed significant differential expression of genes involved in phosphotransferase systems, oxidative phosphorylation, cell morphology, motility, and biofilm formation. Genes in the acetoin biosynthesis pathway were upregulated, suggesting that L. monocytogenes shifts to metabolizing pyruvate to acetoin under organic acid stress. We also identified the formation of cell aggregates in microcolonies as a potential relief strategy. A motif search within the first 150 bp upstream of differentially expressed genes identified a novel potential regulatory sequence that may have a function in the regulation of virulence gene expression. Our data support a model where an excess of intracellular H+ ions is counteracted by pumping H+ out of the cytosol via cytochrome C under reduced activity of the ATP synthase. The observed morphological changes suggest that acid stress may cause cells to aggregate in biofilm microcolonies to create a more favorable microenvironment. Additionally, HCl stress in the host stomach may serve as (i) a signal to downregulate highly immunogenic flagella, and (ii) as an indicator for the imminent contact with host cells which triggers early stage virulence genes.

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