The gut microbiota

Abstract

The most densely populated microbial ecosystem that colonizes the human body is located in the gut and is commonly referred to as gut microbiota. This microbial community encompasses trillions of bacteria with an estimated biomass of 1.5 kg, a size that is similar to the liver, the largest organ in the body. It is tempting to consider the gut microbiota as an organ itself, composed of 1,000-1,200 cell types (species) that encode 150-fold more genes (microbiome) than we have in our own genome. The gut microbiota is highly dynamic and exhibits temporal (age) and spatial (along and across the length of the gut) variations. Furthermore, the intestinal microbial composition is responsive to host genetics, diet, ingested drugs, and a wide number of other environmental factors. The gut microbiota plays a fundamental role in human health, as it evolved specific functions that complement human metabolism and physiology. As an example, intestinal bacteria exhibit specific functions involved in fermentation of polysaccharides to bioavailable nutrients that may also act as signaling component. Moreover, intestinal bacteria take part in vitamin production, regulation of hormone synthesis, and maturation of the immune system. Hence, dysbiosis of the gut microbiota has been implicated in many human diseases such as inflammatory bowel disease, obesity, diabetes, and celiac disease.