Some science behind the scenes

Intestinal flora

The human body carries about 100 trillion microorganisms in its intestines, a number ten times greater than the total number of human cells in the body. It is estimated that these gut flora have around a hundred times as many genes in aggregate as there are in the human genome. 

The number of bacteria in the human intestine is
higher than the number of body cells

Bacteria make up most of the flora in the colon.   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, protozoa, and archaea also make up a part of the gut flora, but little is known about their activities, all that is known is they work for us, not against us. 

Not all the species in the gut have been identified because most cannot be cultured, and identification is difficult.

The four dominant phylum in the human gut are Firmicutes, Bacteroidetes, Actinobacteria, and Proteobacteria. Most bacteria belong to the genera Bacteroides, Clostridium, Fusobacterium, Eubacterium, Ruminococcus, Peptococcus, Peptostreptococcus, and Bifidobacterium. Other genera, such as Escherichia and Lactobacillus, are present to a lesser extent.

Species from the genus Bacteroides alone constitute about 30% of all bacteria in the gut, suggesting that this genus is especially important in the functioning of the host.  The currently known genera of fungi of the gut flora include Candida, Saccharomyces, Aspergillus, and PenicilliumArchaea constitute another large class of gut flora which are important in the metabolism of the bacterial products of fermentation.

References

This is a very very good TED talk about intestinal flora and our microbial community in general

Jonathan Eisen: Meet your microbes

Observations

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