Short-Chain Fatty-Acid-Producing Bacteria: Key Components of the Human Gut Microbiota

Short-chain fatty acids (SCFAs) play a key role in health and disease, as they regulate gut homeostasis and their deficiency is involved in the pathogenesis of several disorders, including inflammatory bowel diseases, colorectal cancer, and cardiometabolic disorders. SCFAs are metabolites of specific bacterial taxa of the human gut microbiota, and their production is influenced by specific foods or food supplements, mainly prebiotics, by the direct fostering of these taxa. This Review provides an overview of SCFAs' roles and functions, and of SCFA-producing bacteria, from their microbiological characteristics and taxonomy to the biochemical process that lead to the release of SCFAs. Moreover, we will describe the potential therapeutic approaches to boost the levels of SCFAs in the human gut and treat different related diseases.

The role of microbiome in the development of gluten-related disorders

Gluten-related disorders (GRD) include celiac disease (CD), non celiac gluten sensitivity (NCGS) and wheat allergy (WA), conditions that are associated with the ingestion of gluten-containing food. Gut microbiota composition and function may be involved in the pathogenesis of GRD. In untreated CD the microbiota is characterized by a reduction in beneficial microbes like Lactobacillus and Bifidobacterium and an increase in pathogenic ones such as Bacteroides and E. coli. Dysbiosis is a hallmark of CD, persists across various disease stages and is only partially corrected by a gluten-free diet. NCGS patients show a different microbial profile, with a notable decrease in microbial richness, and an increase of Ruminococcaceae and decrease of Bacteroidetes and Fusobacteria. The increase of certain bacterial groups such as Clostridium and Anaerobacter, in contrast with the decline of Bacteroides and Clostridium XVIII, marks a distinctive microbial signature associated with allergic responses to food. Mechanisms linking the gut microbiota to the development of GRD include effects on the gut barrier function, microbiota-mediated immune response to gluten, and an impact of microbial metabolites on gluten digestion and tolerance. Although the gluten-free diet is the primary therapy of GRDs, treatment with probiotics may contribute to improve the natural history of these disorders, for instance by minimizing the damaging effects of gluten contamination and accelerating the catch-up growth at the beginning of the dietary treatment of CD. Additional high-quality trials are still needed to identify and standardize the use of probiotics/prebiotics in GRDs.