Characterization of the biofilm phenotype of a Listeria monocytogenes mutant deficient in agr peptide sensing. Issue 9 (6th March 2019) - Zetzmann, Marion
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 Δ 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 Δ 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 Δ 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 Δ agrD mutant displayed a significantly reduced viability upon challenge with lysozyme. These results suggest that the biofilm phenotype of the Δ 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. Abstract : A L. monocytogenes mutant deficient in agr peptide sensing displays reduced biofilm formation specifically in diluted complex medium. This defect was not related to reduced presence of extracellular DNA, enhanced sensitivity to osmotic stress, altered flagellar motility, or changes in surface hydrophobicity. Instead, the observed phenotype seems to be related to altered expression in surface proteins resulting in enhanced sensitivity to lysozyme.