The human microbiome describes the genes associated with all the microorganisms that live in and on a human – all 10¹⁴ of them! The microorganisms are mostly bacteria but also include archaea, fungi, eukaryotic microorganisms and viruses. The organs populated by microorganisms include skin, upper respiratory tract, stomach, intestines and urogenital tracts with other areas being found with improved techniques eg the placenta. Most colonisation occurs at and soon after birth, as infants acquire microorganisms from people, surfaces and objects that they encounter.

Human Microbiome Research

The Human Microbiome Project (HMP) was an international research program based in the U.S. that was focused on the functions of gut microbiota. Some 200 researchers used advanced DNA-sequencing techniques to determine what microorganisms are present and in what populations.

Many current research projects are focused on determining the role of the human microbiome in both health and the diseased state. There is no doubt that our knowledge will continue to grow as we find out more about the vast populations of microorganisms that live in and on us.

Gut Microorganisms and Human Metabolism

Most of the microorganisms associated with the human body are found in the gastrointestinal tract (GIT). The gut microbiota is extremely diverse and it has been estimated that from 500-1,000 species of bacteria live in the human GIT (typically described as up to ~3.5kg of bacteria!).

The gut microorganisms are essential for host digestion and nutrition, aiding in digestion by breaking down carbohydrates that humans could not break down on their own, by liberating short chain fatty acids from indigestible dietary fibres. In addition, they produce vitamins such as biotin and vitamin K.

Human Microbiome and Disease

There has been increased interest in the microbial gut population profiles, due to the possibility that it might play a role in obesity and metabolic syndrome. Research has shown that obese mice have a microbial gut community that differs from the microorganisms found in the gut of non-obese mice, with more Firmicutes bacteria and methanogenic Archaea. It has been suggested that these microorganisms are more efficient at absorbing nutrients.

It has been shown that microbiota changes are associated with diseased states or dysbiosis. Preliminary research has shown that the microbiota might be associated rheumatoid arthritis, colorectal cancer, diabetes and obesity.