A single point mutation in the ribosomal gene enables SigB activation independently of the stressosome and the anti-sigma factor antagonist RsbV.

Microbial population heterogeneity leads to different stress responses and growth behavior of individual cells in a population. Previously, a point mutation in the gene () encoding ribosomal protein S21 was identified in a LO28 variant, which leads to increased multi-stress resistance and a reduced maximum specific growth rate. However, the underlying mechanisms of these phenotypic changes remain unknown.

The impact of different acidic conditions and food substrates on Listeria monocytogenes biofilms development and removal using nanoencapsulated carvacrol.

Listeria monocytogenes biofilms present a significant challenge in the food industry. This study explores the impact of different acidic conditions of culture media and food matrices on the development and removal of biofilms developed on stainless steel surfaces by wild-type (WT) L. monocytogenes strains as well as in two mutant derivatives, ΔsigB and ΔagrA, that have defects in the general stress response and quorum sensing, respectively.

A novel RofA-family transcriptional regulator, GadR, controls the development of acid resistance in .

The ability to survive the acidic conditions found in the stomach is crucial for the food-borne pathogen to gain access to the mammalian gastrointestinal tract. Little is currently known about how acid resistance is regulated in this pathogen and why this trait is highly variable between strains. Here, we used comparative genomics to identify a novel RofA-family transcriptional regulator, GadR, that controls the development of acid resistance.

Manganese uptake mediated by the NRAMP-type transporter MntH is required for acid tolerance in Listeria monocytogenes.

Listeria monocytogenes is a foodborne pathogen that is characterized by its ability to withstand mild stresses (i.e. cold, acid, salt) often encountered in food products or food processing environments.

Trehalose transport occurs via TreB in Listeria monocytogenes and it influences biofilm development and acid resistance.

Listeria monocytogenes is a pathogenic bacterium that can inhabit a diverse range of environmental niches. This is largely attributed to the high proportion of carbohydrate-specific phosphotransferase system (PTS) genes in its genome. Carbohydrates can be assimilated as sources of energy but additionally they can serve as niche-specific cues for L.

The stressosome is required to transduce low pH signals leading to increased transcription of the amino acid-based acid tolerance mechanisms in .

Increasing proton concentration in the environment represents a potentially lethal stress for single-celled microorganisms. To survive in an acidifying environment, the foodborne pathogen quickly activates the alternative sigma factor B (σ), resulting in upregulation of the general stress response (GSR) regulon. Activation of σ is regulated by the stressosome, a multi-protein sensory complex involved in stress detection and signal transduction.

Evolution of Listeria monocytogenes Reveals Selective Pressure for Loss of SigB and AgrA Function at Different Incubation Temperatures.

The alternative sigma factor B (σ) contributes to the stress tolerance of the foodborne pathogen Listeria monocytogenes by upregulating the general stress response. We previously showed that σ loss-of-function mutations arise frequently in strains of L. monocytogenes and suggested that mild stresses might favor the selection of such mutations.

Acid stress signals are integrated into the σB-dependent general stress response pathway via the stressosome in the food-borne pathogen Listeria monocytogenes.

The general stress response (GSR) in Listeria monocytogenes plays a critical role in the survival of this pathogen in the host gastrointestinal tract. The GSR is regulated by the alternative sigma factor B (σB), whose role in protection against acid stress is well established. Here, we investigated the involvement of the stressosome, a sensory hub, in transducing low pH signals to induce the GSR.

Evolutionary trade-offs between growth and survival: The delicate balance between reproductive success and longevity in bacteria.

All living cells strive to allocate cellular resources in a way that promotes maximal evolutionary fitness. While there are many competing demands for resources the main decision making process centres on whether to proceed with growth and reproduction or to "hunker down" and invest in protection and survival (or to strike an optimal balance between these two processes). The transcriptional programme active at any given time largely determines which of these competing processes is dominant.

Activation of the Listeria monocytogenes Stressosome in the Intracellular Eukaryotic Environment.

Listeria monocytogenes is a ubiquitous environmental bacterium and intracellular pathogen that responds to stress using predominantly the alternative sigma factor SigB. Stress is sensed by a multiprotein complex, the stressosome, extensively studied in bacteria grown in nutrient media. Following signal perception, the stressosome triggers a phosphorylation cascade that releases SigB from its anti-sigma factor.

Impact of osmotic stress on the phosphorylation and subcellular location of Listeria monocytogenes stressosome proteins.

Listeria monocytogenes responds to environmental stress using a supra-macromolecular complex, the stressosome, to activate the stress sigma factor SigB. The stressosome structure, inferred from in vitro-assembled complexes, consists of the core proteins RsbR (here renamed RsbR1) and RsbS and, the kinase RsbT. The active complex is proposed to be tethered to the membrane and to support RsbR1/RsbS phosphorylation by RsbT and the subsequent release of RsbT following signal perception.

Comparative Review of the Responses of and to Low pH Stress.

Acidity is one of the principal physicochemical factors that influence the behavior of microorganisms in any environment, and their response to it often determines their ability to grow and survive. Preventing the growth and survival of pathogenic bacteria or, conversely, promoting the growth of bacteria that are useful (in biotechnology and food production, for example), might be improved considerably by a deeper understanding of the protective responses that these microorganisms deploy in the face of acid stress. In this review, we survey the molecular mechanisms used by two unrelated bacterial species in their response to low pH stress.

The σ-Mediated General Stress Response of : Life and Death Decision Making in a Pathogen.

Sensing and responding to environmental cues is critical for the adaptability and success of the food-borne bacterial pathogen . A supramolecular multi-protein complex known as the stressosome, which acts as a stress sensing hub, is responsible for orchestrating the activation of a signal transduction pathway resulting in the activation of σ, the sigma factor that controls the general stress response (GSR). When σ is released from the anti-sigma factor RsbW, a rapid up-regulation of the large σ regulon, comprised of ≥ 300 genes, ensures that cells respond appropriately to the new environmental conditions.

Amino acids other than glutamate affect the expression of the GAD system in Listeria monocytogenes enhancing acid resistance.

The Glutamate Decarboxylase (GAD) system is important for survival of L. monocytogenes and other microorganisms under acidic conditions. Environmental conditions influence the function of the GAD system.

Mild Stress Conditions during Laboratory Culture Promote the Proliferation of Mutations That Negatively Affect Sigma B Activity in Listeria monocytogenes.

In , the full details of how stress signals are integrated into the σ regulatory pathway are not yet available. To help shed light on this question, we investigated a collection of transposon mutants that were predicted to have compromised activity of the alternative sigma factor B (σ). These mutants were tested for acid tolerance, a trait that is known to be under σ regulation, and they were found to display increased acid sensitivity, similar to a mutant lacking σ (Δ).

Different carbon sources result in differential activation of sigma B and stress resistance in Listeria monocytogenes.

Listeria monocytogenes is an important food-borne pathogen that is ubiquitous in the environment. It is able to utilize a variety of carbon sources, to produce biofilms on food-processing surfaces and to survive food preservation-associated stresses. In this study, we investigated the effect of three common carbon sources, namely glucose, glycerol and lactose, on growth and activation of the general stress response Sigma factor, SigB, and corresponding phenotypes including stress resistance.

Blue Light Sensing in Is Temperature-Dependent and the Transcriptional Response to It Is Predominantly SigB-Dependent.

is an important food-borne pathogen that is tolerant to many of the stresses commonly used during food preservation. Outside the host, the bacterium has a saprophytic lifestyle that includes periodic exposure to solar irradiance. The blue component of this light is known to influence the activity of the stress-inducible sigma factor Sigma B (σ).

The σ-dependent regulatory sRNA Rli47 represses isoleucine biosynthesis in through a direct interaction with the transcript.

The facultative intracellular pathogen can persist and grow in a diverse range of environmental conditions, both outside and within its mammalian host. The alternative sigma factor Sigma B (σ) plays an important role in this adaptability and is critical for the transition into the host. While some of the functions of the σ regulon in facilitating this transition are understood the role of σ-dependent small regulatory RNAs (sRNAs) remain poorly characterized.

The Role of Stress and Stress Adaptations in Determining the Fate of the Bacterial Pathogen in the Food Chain.

The foodborne pathogen is a highly adaptable organism that can persist in a wide range of environmental and food-related niches. The consumption of contaminated ready-to-eat foods can cause infections, termed listeriosis, in vulnerable humans, particularly those with weakened immune systems. Although these infections are comparatively rare they are associated with high mortality rates and therefore this pathogen has a significant impact on food safety.

Loss of SigB in Listeria monocytogenes Strains EGD-e and 10403S Confers Hyperresistance to Hydrogen Peroxide in Stationary Phase under Aerobic Conditions.

Unlabelled: SigB is the main stress gene regulator in Listeria monocytogenes affecting the expression of more than 150 genes and thus contributing to multiple-stress resistance. Despite its clear role in most stresses, its role in oxidative stress is uncertain, as results accompanying the loss of sigB range from hyperresistance to hypersensitivity. Previously, these differences have been attributed to strain variation.

Divergent evolution of the activity and regulation of the glutamate decarboxylase systems in Listeria monocytogenes EGD-e and 10403S: roles in virulence and acid tolerance.

The glutamate decarboxylase (GAD) system has been shown to be important for the survival of Listeria monocytogenes in low pH environments. The bacterium can use this faculty to maintain pH homeostasis under acidic conditions. The accepted model for the GAD system proposes that the antiport of glutamate into the bacterial cell in exchange for γ-aminobutyric acid (GABA) is coupled to an intracellular decarboxylation reaction of glutamate into GABA that consumes protons and therefore facilitates pH homeostasis.

Using enhanced green fluorescent protein (EGFP) promoter fusions to study gene regulation at single cell and population levels.

Reporter gene fusions based on the enhanced green fluorescent protein (EGFP) are powerful experimental tools that allow real-time changes in gene expression to be monitored both in single cells and in populations. Here we describe the development of a chromosomally integrated transcriptional reporter fusion in Listeria monocytogenes that allows real-time measurements of gene expression. To construct a single copy of an EGFP-based fluorescent reporter fused to a promoter of interest (Px) in L.

Effects of growth phase and temperature on σB activity within a Listeria monocytogenes population: evidence for RsbV-independent activation of σB at refrigeration temperatures.

The alternative sigma factor σB of Listeria monocytogenes is responsible for regulating the transcription of many of the genes necessary for adaptation to both food-related stresses and to conditions found within the gastrointestinal tract of the host. The present study sought to investigate the influence of growth phase and temperature on the activation of σB within populations of L. monocytogenes EGD-e wild-type, ΔsigB, and ΔrsbV throughout growth at both 4°C and 37°C, using a reporter fusion that couples expression of EGFP to the strongly σB-dependent promoter of lmo2230.

Functional γ-Aminobutyrate Shunt in Listeria monocytogenes: role in acid tolerance and succinate biosynthesis.

Listeria monocytogenes, the causative agent of human listeriosis, is known for its ability to withstand severe environmental stresses. The glutamate decarboxylase (GAD) system is one of the principal systems utilized by the bacterium to cope with acid stress, a reaction that produces γ-aminobutyrate (GABA) from glutamate. Recently, we have shown that GABA can accumulate intracellularly under acidic conditions, even under conditions where no extracellular glutamate-GABA exchange is detectable.