Making Sense of Quorum Sensing at the Intestinal Mucosal Interface

Quorum sensing of Bifidobacteria: Research and progress

Quorum sensing (QS) is a common method of communication among bacteria. While previous studies have discovered the mechanisms of QS in a variety of pathogenic bacteria, relatively little research has focused on probiotics, such as Bifidobacteria. Recent studies have detected QS signalling molecules in Bifidobacteria, but it remains unclear whether the probiotic properties of Bifidobacteria are mediated by QS. This review aims to provide an overview of the QS system in Bifidobacteria and its role in promoting the secretion of metabolites such as extracellular vesicles and biofilms. The review further examines the inhibition of virulence gene expression by Bifidobacteria QS through the luxS/AI-2 system, as well as its role in promoting host-microbial interactions. Understanding the QS mechanisms of Bifidobacteria can reveal beneficial interactions with hosts, which may facilitate the control of bacterial infections, including therapeutic strategies for intestinal diseases. This knowledge can also help improve gut health, thereby addressing the opportunities and challenges of enhancing the body's nutritional status.

Toxigenic Clostridium perfringens Isolated from At-Risk Paediatric Inflammatory Bowel Disease Patients

BACKGROUND AND AIMS

This study aimed to identify microbial drivers of inflammatory bowel disease [IBD], by investigating mucosal-associated bacteria and their detrimental products in IBD patients.

METHODS

We directly cultured bacterial communities from mucosal biopsies from paediatric gastrointestinal patients and examined for pathogenicity-associated traits. Upon identifying Clostridium perfringens as toxigenic bacteria present in mucosal biopsies, we isolated strains and further characterized toxicity and prevalence.

RESULTS

Mucosal biopsy microbial composition differed from corresponding stool samples. C. perfringens was present in eight of nine patients' mucosal biopsies, correlating with haemolytic activity, but was not present in all corresponding stool samples. Large IBD datasets showed higher C. perfringens prevalence in stool samples of IBD adults [18.7-27.1%] versus healthy controls [5.1%]. In vitro, C. perfringens supernatants were toxic to cell types beneath the intestinal epithelial barrier, including endothelial cells, neuroblasts, and neutrophils, while the impact on epithelial cells was less pronounced, suggesting C. perfringens may be particularly damaging when barrier integrity is compromised. Further characterization using purified toxins and genetic insertion mutants confirmed perfringolysin O [PFO] toxin was sufficient for toxicity. Toxin RNA signatures were found in the original patient biopsies by PCR, suggesting intestinal production. C. perfringens supernatants also induced activation of neuroblast and dorsal root ganglion neurons in vitro, suggesting C. perfringens in inflamed mucosal tissue may directly contribute to abdominal pain, a frequent IBD symptom.

CONCLUSIONS

Gastrointestinal carriage of certain toxigenic C. perfringens may have an important pathogenic impact on IBD patients. These findings support routine monitoring of C. perfringens and PFO toxins and potential treatment in patients.

Quorum sensing-related activities of beneficial and pathogenic bacteria have important implications for plant and human health

Eukaryotic organisms coevolved with microbes from the environment forming holobiotic meta-genomic units. Members of host-associated microbiomes have commensalic, beneficial/symbiotic, or pathogenic phenotypes. More than 100 years ago, Lorenz Hiltner, pioneer of soil microbiology, introduced the term 'Rhizosphere' to characterize the observation that a high density of saprophytic, beneficial, and pathogenic microbes are attracted by root exudates. The balance between these types of microbes decide about the health of the host. Nowadays we know, that for the interaction of microbes with all eukaryotic hosts similar principles and processes of cooperative and competitive functions are in action. Small diffusible molecules like (phyto)hormones, volatiles and quorum sensing signals are examples for mediators of interspecies and cross-kingdom interactions. Quorum sensing of bacteria is mediated by different autoinducible metabolites in a density-dependent manner. In this perspective publication, the role of QS-related activities for the health of hosts will be discussed focussing mostly on N-acyl-homoserine lactones (AHL). It is also considered that in some cases very close phylogenetic relations exist between plant beneficial and opportunistic human pathogenic bacteria. Based on a genome and system-targeted new understanding, sociomicrobiological solutions are possible for the biocontrol of diseases and the health improvement of eukaryotic hosts.

The gut microbiome of farmed Arctic char (Salvelinus alpinus) is shaped by feeding stage and nutrient presence

The gut microbiome plays an important role in maintaining health and productivity of farmed fish. However, the functional role of most gut microorganisms remains unknown. Identifying the stable members of the gut microbiota and understanding their functional roles could aid in the selection of positive traits or act as a proxy for fish health in aquaculture. Here, we analyse the gut microbial community of farmed juvenile Arctic char (Salvelinus alpinus) and reconstruct the metabolic potential of its main symbionts. The gut microbiota of Arctic char undergoes a succession in community composition during the first weeks post-hatch, with a decrease in Shannon diversity and the establishment of three dominant bacterial taxa. The genome of the most abundant bacterium, a Mycoplasma sp., shows adaptation to rapid growth in the nutrient-rich gut environment. The second most abundant taxon, a Brevinema sp., has versatile metabolic potential, including genes involved in host mucin degradation and utilization. However, during periods of absent gut content, a Ruminococcaceae bacterium becomes dominant, possibly outgrowing all other bacteria through the production of secondary metabolites involved in quorum sensing and cross-inhibition while benefiting the host through short-chain fatty acid production. Whereas Mycoplasma is often present as a symbiont in farmed salmonids, we show that the Ruminococcaceae species is also detected in wild Arctic char, suggesting a close evolutionary relationship between the host and this symbiotic bacterium.

Bioprospecting and Exploration of Phytochemicals as Quorum Sensing Inhibitors against Cariogenic Dental Biofilm

Dental caries is a polymicrobial infection affecting the dental hard tissues. Excessive carbohydrate intake leads to the accumulation of acid-producing and acid-resistant microorganisms in the oral region. It is a biofilm-dependent oral infection with cariogenic pathogens and the most prevalent disease globally. The prevention and control of caries play a vital role in global health management. Periodontal diseases and subgingival plaque etiology are due to the combined action of bacterial invasion and immune reaction, resulting in the devastation of periodontal tissues, culminating in tooth loss. The compact micro colony inhabiting the dental surfaces attaches with secreted polymer, forming a biofilm. Bacterial biofilm impervious to various drugs and chemicals poses a significant challenge in therapeutic scenarios of medical and odonatological infections. The quorum-sensing signaling mechanism in bacteria controls the metabolic and physiologic properties involved in bacterial existence, pathogenesis, and virulence. Hence, studies monitoring the molecular mechanism of quorum sensing and their restricted social interactions will be highly beneficial in the treatment regimen of the modern era. Natural bioactive compounds can be exploited for their medicinal value in combating oro-dental infections. Phytochemicals are promising candidates that could provide novel strategies for fighting infections. The current review highlights the mechanism of quorum sensing, plant products’ effect in controlling quorum sensing, and biofilm-induced dental infections like Periodontitis.

Vaccine Strategies to Elicit Mucosal Immunity

Vaccines are essential tools to prevent infection and control transmission of infectious diseases that threaten public health. Most infectious agents enter their hosts across mucosal surfaces, which make up key first lines of host defense against pathogens. Mucosal immune responses play critical roles in host immune defense to provide durable and better recall responses. Substantial attention has been focused on developing effective mucosal vaccines to elicit robust localized and systemic immune responses by administration via mucosal routes. Mucosal vaccines that elicit effective immune responses yield protection superior to parenterally delivered vaccines. Beyond their valuable immunogenicity, mucosal vaccines can be less expensive and easier to administer without a need for injection materials and more highly trained personnel. However, developing effective mucosal vaccines faces many challenges, and much effort has been directed at their development. In this article, we review the history of mucosal vaccine development and present an overview of mucosal compartment biology and the roles that mucosal immunity plays in defending against infection, knowledge that has helped inform mucosal vaccine development. We explore new progress in mucosal vaccine design and optimization and novel approaches created to improve the efficacy and safety of mucosal vaccines.

The importance of the gut microbiome and its signals for a healthy nervous system and the multifaceted mechanisms of neuropsychiatric disorders

Increasing evidence links the gut microbiome and the nervous system in health and disease. This narrative review discusses current views on the interaction between the gut microbiota, the intestinal epithelium, and the brain, and provides an overview of the communication routes and signals of the bidirectional interactions between gut microbiota and the brain, including circulatory, immunological, neuroanatomical, and neuroendocrine pathways. Similarities and differences in healthy gut microbiota in humans and mice exist that are relevant for the translational gap between non-human model systems and patients. There is an increasing spectrum of metabolites and neurotransmitters that are released and/or modulated by the gut microbiota in both homeostatic and pathological conditions. Dysbiotic disruptions occur as consequences of critical illnesses such as cancer, cardiovascular and chronic kidney disease but also neurological, mental, and pain disorders, as well as ischemic and traumatic brain injury. Changes in the gut microbiota (dysbiosis) and a concomitant imbalance in the release of mediators may be cause or consequence of diseases of the central nervous system and are increasingly emerging as critical links to the disruption of healthy physiological function, alterations in nutrition intake, exposure to hypoxic conditions and others, observed in brain disorders. Despite the generally accepted importance of the gut microbiome, the bidirectional communication routes between brain and gut are not fully understood. Elucidating these routes and signaling pathways in more detail offers novel mechanistic insight into the pathophysiology and multifaceted aspects of brain disorders.

The Role of the Gut Microbiome in Cancer: A Review, With Special Focus on Colorectal Neoplasia and Clostridioides difficile

The gut microbiome has coevolved with humans to aid in physiologic functions and prevent disease. An increasing prevalence of gut dysbiosis in modern society exists and has strong linkages to multiple disease processes common in the developed world. Mechanisms for microbiome-human interactions that impact host homeostasis include bacterial metabolite/toxin production, biofilm formation with mucous layer infiltration, and host immune system modulation. Most of this crosstalk occurs at the epithelial layer of the gut, and as such the role of these interactions in the induction of colorectal cancer-a highly prevalent disease globally and one undergoing significant epidemiologic shifts-is under increasing scrutiny. Although multiple individual gut bacteria have been hypothesized as possible driver organisms in the oncogenic process, no bacterium has been definitively identified as a causal agent of colorectal cancer, suggesting that host lifestyle factors, microbiome community interactions, and the mucosal and/or systemic immune response may play a critical role in the process. Recent evidence has emerged implicating the ubiquitous human pathogen Clostridioides difficile as a possible promoter of colorectal cancer through chronic toxin-mediated cellular changes. Although much remains to be defined regarding the natural history of infections caused by this pathogen and its potential for oncogenesis, it provides a strong model for the role of both individual bacteria and of the gut microbial community as a whole in the development of colorectal cancer.

Microbes, oxytocin and stress: Converging players regulating eating behavior

Oxytocin is a peptide-hormone extensively studied for its multifaceted biological functions and has recently gained attention for its role in eating behavior, through its action as an anorexigenic neuropeptide. Moreover, the gut microbiota is involved in oxytocinergic signaling through the brain-gut axis, specifically in the regulation of social behavior. The gut microbiota is also implicated in appetite regulation and is postulated to play a role in central regulation of hedonic eating. In this review, we provide an overview on oxytocin and its individual links with the microbiome, the homeostatic and non-homeostatic regulation of eating behavior as well as social behavior and stress.

Diffusible signal factors (DSFs) bind and repress VirF, the leading virulence activator of Shigella flexneri

Shigella, the aetiological agent of human bacillary dysentery, controls the expression of its virulence determinants through an environmentally stimulated cascade of transcriptional activators. VirF is the leading activator and is essential for proper virulence expression. In this work, we report on in vitro and in vivo experiments showing that two autoinducers of the DSF family, XcDSF and BDSF interact with the jelly roll module of VirF causing its inhibition and affecting the expression of the entire virulence system of Shigella, including its ability to invade epithelial cells. We propose a molecular model explaining how the binding of XcDSF and BDSF causes inhibition of VirF by preventing its dimerization. Overall, our experimental results suggest that XcDSF and BDSF may contribute to "colonisation resistance" in the human gut or, alternatively, may be exploited for the fine-tuning of Shigella virulence expression as the bacterium migrates from the lumen to approach the intestinal mucosa. Our findings also stress how a detailed understanding of the interaction of DSF ligands with VirF may contribute to the rational development of innovative antivirulence drugs to treat shigellosis.

Differential Proteomic Analysis of Listeria monocytogenes during High-Pressure Processing

Simple Summary

High-pressure processing (HPP) is a prevailing non-thermal food preservation technology. The inactivation mechanisms of Listeria monocytogenes under sub-lethal to lethal damage by different levels of HPP treatments were conducted by label-free quantitative proteomic analysis. HPP might promote translation initiation due to upregulation of most ribosomal subunits and initiation factors. However, protein synthesis was arrested according to the shortage of proteins responsible for elongation, termination and recycling. The quantitative proteomics approaches provide fundamental information on L. monocytogenes under different HPP pressures, and provide theoretical support for HPP against Listeriosis illness and for promotion of safer ready-to-eat foods.

Abstract

High-pressure processing (HPP) is a prevailing non-thermal food preservation technology. The inactivation mechanisms of Listeria monocytogenes under HPP at 200 and 400 MPa for 3 min were investigated by label-free quantitative proteomic analysis and functional enrichment analysis in the Kyoto Encyclopedia of Genes and Genomes. HPP treatment at 400 MPa exhibited significant effects on proteins involved in translation, carbon, carbohydrate, lipid and energy metabolism, and peptidoglycan biosynthesis. HPP increased most ribosomal subunits and initiation factors, suggesting it might shift ribosomal biogenesis to translation initiation. However, protein synthesis was impaired by the shortage of proteins responsible for elongation, termination and recycling. HPP stimulated several ATP-dependent Clp proteases, and the global transcriptional regulator Spx, associating with activation of the stress-activated sigma factor Sigma B (σ^B) and the transcriptional activator positive regulatory factor A (PrfA) regulons. The quantitative proteomics approaches provide fundamental information on L. monocytogenes under different HPP pressures, and provide theoretical support for HPP against Listeriosis illness and for promotion of safer ready-to-eat foods.