Role of the Human Gut Microbiota in Health and Disease

Dear Colleagues,

The human gut microbiota, composed of trillions of microorganisms, including bacteria, viruses, fungi, and protozoa, plays a crucial role in maintaining overall health and influencing disease states. The gut microbiota is primarily located in the colon, and its composition and functions are influenced by various factors, including diet, genetics, environment, and lifestyle. The role of the microbiota in good health or, conversely, in the onset of pathologies is regularly enriched by new scientific data of interest.

This Special Issue aims to cover various fields such as its role in health regarding digestion and metabolism, fermentation of dietary fibers to produce short-chain fatty acids (SCFAs) such as acetate, propionate, and butyrate, which are important energy sources for colon cells and play roles in metabolism and immune regulation, or the synthesis of essential vitamins such as vitamin K and some B vitamins, which are critical for blood clotting and metabolic functions. The gut microbiota is crucial for the development and function of the immune system. It helps in the maturation of immune cells and the production of antibodies. The microbiota competes with pathogenic microbes for nutrients and attachment sites, producing antimicrobial substances and maintaining the integrity of the gut barrier, or enhances the integrity of the intestinal barrier by promoting the production of mucus and tight junction proteins, preventing the translocation of harmful substances and pathogens into the bloodstream. It also influences the gut–brain axis, affecting mood, behavior, and cognitive functions. It produces neurotransmitters and metabolites that can impact brain function and mental health. Beyond its many beneficial aspects, the microbiota can play a key role in the onset of pathologies such as inflammatory bowel disease (IBD), where dysbiosis, an imbalance in the gut microbiota, is associated with Crohn's disease and ulcerative colitis, in which the altered microbiota composition contributes to inflammation and immune dysregulation. Dysbiosis is also frequently combined with obesity and type 2 diabetes, in which the gut microbiota affects energy extraction from food, fat storage, and insulin sensitivity. Early-life microbiota composition affects immune system development and the risk of developing allergies and asthma. Reduced microbial diversity and delayed colonization by beneficial bacteria are linked to these conditions. Dysbiosis is implicated in autoimmune diseases like rheumatoid arthritis and multiple sclerosis. The microbiota influences immune tolerance and autoimmunity. Alterations in the gut microbiota are associated with depression and anxiety. The microbiota produces neuroactive compounds and influences the hypothalamic–pituitary–adrenal (HPA) axis, impacting stress responses and mental health. Dysbiosis is linked to colorectal cancer through mechanisms such as inflammation, genotoxin production, and modulation of the host's immune response. Certain bacterial species can promote tumorigenesis. Some therapeutic interventions may be beneficial, such as supplementation with probiotics and prebiotics, fecal microbiota transplantation, dietary modifications, and antibiotic treatment. Understanding the complex interplay between the gut microbiota and human health is critical for developing novel therapeutic strategies for various diseases. The gut microbiota's influence spans numerous aspects of health, making it a pivotal area of research in modern medicine. We are pleased to invite you to submit any original article or review relating to the various aspects listed above for publication in this Special Issue. We look forward to receiving your contributions.

Dr. Jerome Gay-Quéheillard
Guest Editor

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• microbiota
• dysbiosis
• gut epithelial barrier
• IBD
• brain–gut axis
• obesity
• anxiety
• depression
• immune system
• prebiotics
• probiotics