Cyclic di-GMP-dependent signaling pathways in the pathogenic Firmicute Listeria monocytogenes

• Published in: PLoS pathogens 2014-08, Vol.10 (8), p.e1004301-e1004301
• Main Authors: Chen, Li-Hong, Köseoğlu, Volkan K, Güvener, Zehra T, Myers-Morales, Tanya, Reed, Joseph M, D'Orazio, Sarah E F, Miller, Kurt W, Gomelsky, Mark
• Format: Article
• Language: English
• Subjects: Analysis; Animals; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Biofilms; Biology and Life Sciences; Chromatography, High Pressure Liquid; Colleges & universities; Cyclic GMP - analogs & derivatives; Cyclic GMP - metabolism; Disease Models, Animal; E coli; Escherichia coli Proteins - metabolism; Experiments; Female; Food contamination; Food contamination & poisoning; Food safety; Gene Expression Regulation, Bacterial - physiology; Genetic aspects; Infections; Listeria; Listeria monocytogenes; Listeria monocytogenes - genetics; Listeria monocytogenes - pathogenicity; Listeriosis - genetics; Listeriosis - metabolism; Medicine and Health Sciences; Mice; Mice, Inbred BALB C; Milk; Mortality; Motility; Phosphorus-Oxygen Lyases - metabolism; Physiological aspects; Proteins; Risk factors; Signal Transduction - physiology; Virulence (Microbiology); Virulence - physiology
• ISSN: 1553-7374; 1553-7366; 1553-7374
• DOI: 10.1371/journal.ppat.1004301

We characterized key components and major targets of the c-di-GMP signaling pathways in the foodborne pathogen Listeria monocytogenes, identified a new c-di-GMP-inducible exopolysaccharide responsible for motility inhibition, cell aggregation, and enhanced tolerance to disinfectants and desiccation, and provided first insights into the role of c-di-GMP signaling in listerial virulence. Genome-wide genetic and biochemical analyses of c-di-GMP signaling pathways revealed that L. monocytogenes has three GGDEF domain proteins, DgcA (Lmo1911), DgcB (Lmo1912) and DgcC (Lmo2174), that possess diguanylate cyclase activity, and three EAL domain proteins, PdeB (Lmo0131), PdeC (Lmo1914) and PdeD (Lmo0111), that possess c-di-GMP phosphodiesterase activity. Deletion of all phosphodiesterase genes (ΔpdeB/C/D) or expression of a heterologous diguanylate cyclase stimulated production of a previously unknown exopolysaccharide. The synthesis of this exopolysaccharide was attributed to the pssA-E (lmo0527-0531) gene cluster. The last gene of the cluster encodes the fourth listerial GGDEF domain protein, PssE, that functions as an I-site c-di-GMP receptor essential for exopolysaccharide synthesis. The c-di-GMP-inducible exopolysaccharide causes cell aggregation in minimal medium and impairs bacterial migration in semi-solid agar, however, it does not promote biofilm formation on abiotic surfaces. The exopolysaccharide also greatly enhances bacterial tolerance to commonly used disinfectants as well as desiccation, which may contribute to survival of L. monocytogenes on contaminated food products and in food-processing facilities. The exopolysaccharide and another, as yet unknown c-di-GMP-dependent target, drastically decrease listerial invasiveness in enterocytes in vitro, and lower pathogen load in the liver and gallbladder of mice infected via an oral route, which suggests that elevated c-di-GMP levels play an overall negative role in listerial virulence.