Human Microbiome Project

The Human Microbiome Project (HMP) was a United States National Institutes of Health (NIH) initiative with the goal of identifying and characterizing the microorganisms which are found in association with both healthy and diseased humans (the human microbiome). Launched in 2008, it was a five-year project, best characterized as a feasibility study, and had a total budget of $115 million. The ultimate goal of this and similar NIH-sponsored microbiome projects was to test how changes in the human microbiome are associated with human health or disease. This topic is currently not well understood.

Important components of the Human Microbiome Project were culture-independent methods of microbial community characterization, such as metagenomics (which provides a broad genetic perspective on a single microbial community), as well as extensive whole genome sequencing (which provides a "deep" genetic perspective on certain aspects of a given microbial community, i.e. of individual bacterial species). The latter served as reference genomic sequences — 3000 such sequences of individual bacterial isolates are currently planned — for comparison purposes during subsequent metagenomic analysis. The microbiology of five body sites was emphasized: oral, skin, vaginal, gut, and nasal/lung. The project also financed deep sequencing of bacterial 16S rRNA sequences amplified by polymerase chain reaction from human subjects.

As of 2014, it was often reported in popular media and in the scientific literature that there are about 10 times as many microbial cells in the human body than there are human cells; this figure was based on estimates that the human microbiome includes around 100 trillion bacterial cells and an adult human typically has around 10 trillion human cells. In 2014 the American Academy of Microbiology published an FAQ that emphasized that the number of microbial cells and the number of human cells are both estimates, and noted that recent research had arrived at a new estimate of the number of human cells at around 37 trillion cells, meaning that the ratio of microbial to human cells is probably about 3:1. In 2016 another group published a new estimate of ratio as being roughly 1:1 (1.3:1, with "an uncertainty of 25% and a variation of 53% over the population of standard 70 kg males").

...
Wikipedia