Gut flora
Bacteria make up most of the flora in the colon and up to 60% of the dry mass of faeces. Somewhere between 300 and 1000 different species live in the gut, with most estimates at about 500. However, it is probable that 99% of the bacteria come from about 30 or 40 species.  Fungi and protozoa also make up a part of the gut flora, but little is known about their activities.