The current issue (February 2008) of Microbiology Today includes a number of articles devoted to the microorganisms that live in our body. In an introductory article (Life on us), Robin Weiss writes:
"As an ecosystem, it has become clear that we are only part human, because a significant amount of our biomass is microbial. In demographic terms, microbes outnumber our own cells. While there are 1014 human cells in the average adult, there are probably ~1015 bacteria and >1017 viruses associated with the human body. In terms of genetic diversity and complexity, the microbial metagenome of humans may be greater than the 3×109 base pairs of human DNA."
So, we are superorganisms, composed of many organisms. In fact, it seems that the collective genome of our microbial symbionts (the microbiome) may contain over 100 times as many genes as our own genome, and provides traits that humans did not need to evolve on their own (from an article in Science).
In Life on us, the author makes another thought-provoking remark:
"Thus while we share >98 % host DNA sequence similarity with the chimpanzee, the microbial and viral species that live on or on us are only ~50 % shared with the great apes."Definitely, those tiny passengers in our bodies should have influenced our evolution. How much of our "humanity" (whatever makes us different from other apes) do we owe to our microbial cells??
A collection of related links (in chronological order, newest first):
- Human Microbiome Project, NIH Roadmap for Medical Research. The official overview of the project (updated Jan. 2008).
- NIH launches Human Microbiome Project. News release, EurekAlert! (Dec. 2007).
- Deciphering the Human Microbiome (and What It Means for Health & Medicine). An explanation for the layperson, Britannica Blog (Dec. 2007).
- The Human Microbiome Project. Insight article at Nature, describing the challenges and the possible rewards of the project, with examples (Oct. 2007).
- Friendly bacteria - we need it and it needs us. Their influence in our health (the "hygiene hypothesis", possible effects on our behavior and our mental health...). Common Ground (Sept. 2007).
- Our Microbial Menagerie, and its effects on our health. Technology Review (July-Aug. 2007).
- Gut check: Tracking the ecosystem within us. The microbes in baby poop, Biology News Net [reporting on a paper from PLoS Biology] (June 2007).
- Metagenomic Analysis of the Human Distal Gut Microbiome. Research article, Science (June 2006).
- People Are Human-Bacteria Hybrid, Wired [reporting on a paper from Nature Biotechnology] (Oct. 2004).
Microbiology = micro + biology
Biology = bio + logy