Gut microbiota are the microorganisms, including bacteria and archaea, that live in the digestive tracts of vertebrates including humans, and of insects.

Alternative terms include gut flora (an outdated term that technically refers to plants) and gut microbiome.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.

In the human, the gut is the main location of human microbiota.

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.

However, 99% of gut bacteria come from about 30 or 40 species.

Bacteria also make up to 60% of the dry mass of feces.

Over 99% of the bacteria in the gut are anaerobes, but in the cecum, aerobic bacteria reach high densities.

It is estimated that the human gut microbiota have around a hundred times as many genes as there are in the human genome.

 The gut microbiota has a wide range of effects, including colonization effects, germ resistance, intestinal epithelium retention,...........

metabolism of dietary and pharmaceutical compounds, immune control, and even behavior through the intestinal-brain axis.