The Virulence and Infectivity of Listeria monocytogenes Are Not Substantially Altered by Elevated SigB Activity.

Listeria monocytogenes is a bacterial pathogen capable of causing severe infections but also thriving outside the host. To respond to different stress conditions, L. monocytogenes mainly utilizes the general stress response regulon, which largely is controlled by the alternative sigma factor Sigma B (SigB).

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.

Molecular insights into intra-complex signal transmission during stressosome activation.

The stressosome is a pseudo-icosahedral megadalton bacterial stress-sensing protein complex consisting of several copies of two STAS-domain proteins, RsbR and RsbS, and the kinase RsbT. Upon perception of environmental stress multiple copies of RsbT are released from the surface of the stressosome. Free RsbT activates downstream proteins to elicit a global cellular response, such as the activation of the general stress response in Gram-positive bacteria.

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.

Listeria monocytogenes Requires the RsbX Protein To Prevent SigB Activation under Nonstressed Conditions.

The survival of microbial cells under changing environmental conditions requires an efficient reprogramming of transcription, often mediated by alternative sigma factors. The Gram-positive human pathogen Listeria monocytogenes senses and responds to environmental stress mainly through the alternative sigma factor σ (SigB), which controls expression of the general stress response regulon. SigB activation is achieved through a complex series of phosphorylation/dephosphorylation events culminating in the release of SigB from its anti-sigma factor RsbW.

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.

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).

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.

Flick of a switch: regulatory mechanisms allowing Listeria monocytogenes to transition from a saprophyte to a killer.

In contrast to obligate intracellular pathogens that can remain in relatively stable host-associated environments, the soil-living bacterial pathogen Listeria monocytogenes has to sense and respond to physical and chemical cues in a variety of quite different niches. In particular, the bacterium has to survive the dramatic transition from its saprophytic existence to life within the host where nutritional stress, increased temperature, acidity, osmotic stress and the host defences present a new and challenging landscape. This review focuses on the σ and PrfA regulatory systems used by L.

Microbial stress meeting: From systems to molecules and back.

The 4th Microbial Stress Meeting: from Systems to Moleculesand Back was held in April 2018 in Kinsale, Ireland. The meeting covered five main topics: 1. Stress at the systems and structural level; 2.

Tracking Human Adenovirus Inactivation by Gamma Radiation under Different Environmental Conditions.

Unlabelled: Adenovirus is the most prevalent enteric virus in waters worldwide due to its environmental stability, which leads to public health concerns. Mitigation strategies are therefore required. The aim of this study was to assess the inactivation of human adenovirus type 5 (HAdV-5) by gamma radiation in aqueous environments.

Microbiological assessment of indoor air quality at different hospital sites.

Poor hospital indoor air quality (IAQ) may lead to hospital-acquired infections, sick hospital syndrome and various occupational hazards. Air-control measures are crucial for reducing dissemination of airborne biological particles in hospitals. The objective of this study was to perform a survey of bioaerosol quality in different sites in a Portuguese Hospital, namely the operating theater (OT), the emergency service (ES) and the surgical ward (SW).