Ecological and evolutionary forces shaping microbial diversity in the human intestine

Ecological and evolutionary forces shaping microbial diversity in the human intestine


Our intestinal tract is a nutrient-rich environment packed with up to 100 trillion (1014) microbes. The vast majority reside in our colon where densities approach 1011–1012 cells/ml, the highest recorded for any microbial habitat. Today, there are 6.5 billion humans living on Earth. Together, we represent a gut reservoir of 1023–1024 microbial cells. This number is just five orders of magnitude less than the world's oceans, which contain an estimated 1029 cells. Therefore, together with other mammals, the human gut constitutes a substantial microbial habitat in our biosphere.