The human microbiome is "the full array of microorganisms (the microbiota) that live on and in humans and, more specifically, the collection of microbial genomes that contribute to the broader genetic portrait, or metagenome, of a human. The genomes that constitute the human microbiome represent a remarkably diverse array of microorganisms that includes bacteria, archaea (primitive single-celled organisms), fungi, and even some protozoans and nonliving viruses. Bacteria are by far the most numerous members of the human microbiome: the bacterial population alone is estimated at between 75 trillion and 200 trillion individual organisms, while the entire human body consists of about 50 trillion to 100 trillion somatic (body) cells. The sheer microbial abundance suggests that the human body is in fact a “supraorganism,” a collection of human and microbial cells and genes and thus a blend of human and microbial traits."
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Rogers, K. (n.d.). Human Microbiome. In Encyclopedia Brittanica online. Retrieved from http://www.britannica.com/science/human-microbiome.