Gut microbiota

Gut microbiota are the microorganisms, including bacteria, archaea, fungi, and viruses that live in the digestive tracts of animals.[1][2] Alternative terms include gut flora (an outdated term that technically refers to plants) and gut microbiome. The gastrointestinal metagenome (sometimes defined as the microbiome) is the aggregate of all the genomes of gut microbiota.[3][4] In the human, the gut is the main location of human microbiota.[5] The gut microbiota has broad impacts, including effects on colonization, resistance to pathogens, maintaining the intestinal epithelium, metabolizing dietary and pharmaceutical compounds, controlling immune function, and even behavior through the gut–brain axis.

Escherichia coli, one of the many species of bacteria present in the human gut

The microbial composition of the gut microbiota varies across regions of the digestive tract. The colon contains the highest microbial density recorded in any habitat on Earth, representing between 300 and 1000 different species.[6] Bacteria are the largest and to date, best studied component and 99% of gut bacteria come from about 30 or 40 species.[7] Up to 60% of the dry mass of feces is bacteria.[8] Over 99% of the bacteria in the gut are anaerobes, but in the cecum, aerobic bacteria reach high densities.[5] It is estimated that the human gut microbiota have around a hundred times as many genes as there are in the human genome.

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