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Characterization of the biofilm phenotype of a Listeria monocytogenes mutant deficient in agr peptide sensing.

ABSTRACT: Listeria monocytogenes is a food-borne human pathogen and a serious concern in food production and preservation. Previous studies have shown that biofilm formation of L. monocytogenes and presence of extracellular DNA (eDNA) in the biofilm matrix varies with environmental conditions and may involve agr peptide sensing. Experiments in normal and diluted (hypoosmotic) complex media at different temperatures revealed reduced biofilm formation of L. monocytogenes EGD-e ?agrD, a mutant deficient in agr peptide sensing, specifically in diluted Brain Heart Infusion at 25°C. This defect was not related to reduced sensitivity to DNase treatment suggesting sufficient levels of eDNA. Re-analysis of a previously published transcriptional profiling indicated that a total of 132 stress-related genes, that is 78.6% of the SigB-dependent stress regulon, are differentially expressed in the ?agrD mutant. Additionally, a number of genes involved in flagellar motility and a large number of other surface proteins including internalins, peptidoglycan binding and cell wall modifying proteins showed agr-dependent gene expression. However, survival of the ?agrD mutant in hypoosmotic conditions or following exposure to high hydrostatic pressure was comparable to the wild type. Also, flagellar motility and surface hydrophobicity were not affected. However, the ?agrD mutant displayed a significantly reduced viability upon challenge with lysozyme. These results suggest that the biofilm phenotype of the ?agrD mutant is not a consequence of reduced resistance to hypoosmotic or high pressure stress, motility or surface hydrophobicity. Instead, agr peptide sensing seems to be required for proper regulation of biosynthesis, structure and function of the cell envelope, adhesion to the substratum, and/or interaction of bacteria within a biofilm.

SUBMITTER: Zetzmann M

PROVIDER: S-EPMC6741131 | biostudies-literature | 2019 Sep

REPOSITORIES: biostudies-literature

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Characterization of the biofilm phenotype of a Listeria monocytogenes mutant deficient in agr peptide sensing.

Zetzmann Marion M Bucur Florentina Ionela FI Crauwels Peter P Borda Daniela D Nicolau Anca Ioana AI Grigore-Gurgu Leontina L Seibold Gerd M GM Riedel Christian U CU

MicrobiologyOpen 20190306 9

Listeria monocytogenes is a food-borne human pathogen and a serious concern in food production and preservation. Previous studies have shown that biofilm formation of L. monocytogenes and presence of extracellular DNA (eDNA) in the biofilm matrix varies with environmental conditions and may involve agr peptide sensing. Experiments in normal and diluted (hypoosmotic) complex media at different temperatures revealed reduced biofilm formation of L. monocytogenes EGD-e ΔagrD, a mutant deficient in a ...[more]

PMID: 30843349

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Project description:Listeria monocytogenes (Lm) is an important food-borne human pathogen that is able to strive under a wide range of environmental conditions. Its accessory gene regulator (agr) system was shown to impact on biofilm formation and virulence and has been proposed as one of the regulatory mechanisms involved in adaptation to these changing environments. The Lm agr operon is homologous to the Staphylococcus aureus system, which includes an agrD-encoded autoinducing peptide that stimulates expression of the agr genes via the AgrCA two-component system and is required for regulation of target genes. The aim of the present study was to identify the native autoinducing peptide (AIP) of Lm using a luciferase reporter system in wildtype and agrD deficient strains, rational design of synthetic peptides and mass spectrometry. Upon deletion of agrD, luciferase reporter activity driven by the PII promoter of the agr operon was completely abolished and this defect was restored by co-cultivation of the agrD-negative reporter strain with a producer strain. Based on the sequence and structures of known AIPs of other organisms, a set of potential Lm AIPs was designed and tested for PII-activation. This led to the identification of a cyclic pentapeptide that was able to induce PII-driven luciferase reporter activity and restore defective invasion of the agrD deletion mutant into Caco-2 cells. Analysis of supernatants of a recombinant Escherichia coli strain expressing AgrBD identified a peptide identical in mass and charge to the cyclic pentapeptide. The Lm agr system is specific for this pentapeptide since the AIP of Lactobacillus plantarum, which also is a pentapeptide yet with different amino acid sequence, did not induce PII activity. In summary, the presented results provide further evidence for the hypothesis that the agrD gene of Lm encodes a secreted AIP responsible for autoregulation of the agr system of Lm. Additionally, the structure of the native Lm AIP was identified.

Dataset Information

Characterization of the biofilm phenotype of a Listeria monocytogenes mutant deficient in agr peptide sensing.

Publications

Characterization of the biofilm phenotype of a Listeria monocytogenes mutant deficient in agr peptide sensing.

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