Confusion about the species richness of human gut microbiota

A key message from a range of high profile next generation sequencing studies on the human microbiota is that it composes a tremendously rich community of more than 1000 species within each one of us. Although more recent studies have shown estimates of between 100 and 200 species per individual, this has not yet been made clear in the literature. Currently, the most widely accepted estimate of species richness is therefore five to ten times too high. Here, we will review the different estimates of species richness in the literature, address potential sources of artefacts, the reluctance to correct these, and provide suggestions for future directions.