On the drive home yesterday afternoon I heard a fascinating story on NPR about an ecosystem near and dear to all humans - our skin. Even if bacteria aren't your thing, the story and the findings are really interesting (and actually could be applicable to a wide host of conditions and diseases).

Now, any good microbiology student knows about the vast swath of bacteria that live in and on our bodies. (Have you ever swabbed your belly button and grown the resultant unicellular life on a petri dish? Very cool.) But scientists working on the Human Microbiome Project revealed that the human body contains 10 times as many bacterial cells as it does human cells, according to the NPR report. They also found that bacteria are "part of genuine ecosystems — akin to life on the savannah, the ocean or the rich life of a tropical rain forest."

"We think of the skin as a desert," says Julie Segre, who studies skin, the body's largest organ, at the National Human Genome Research Institute. "But within the desert of our dry skin, there are these streams, and those are the creases of our bodies. And then there are the oases, so places that are very moist and rich. That would be something like the underarm or the bellybutton."
The researchers sampled "the bacterial wildlife" from 20 different spots on the bodies of 10 healthy volunteers. The spots were chosen because they are associated with different dermatological conditions - eczema and psoriasis, for example.

What they found was quite startling - even though the skin cells might be the same and the proximity quite close (eczema on the inside of the elbow, psoriasis on the outside), the bacteria are completely different! Why does that matter? Well, even though psoriasis and eczema don't appear to be caused by bacteria, they could be a reaction, triggered by a change in the ecosystems of the bacteria on our skin.

The most diverse spot on your skin? The forearm, with 44 bacteria species on average, according to this LiveScience article. By comparison, behind the ear saw only 19 bacteria species on average.

"So when we think about what promotes health and what causes disease, we have to consider that it could be the bacteria and the fungi and the other microorganisms that live together with us — that they could be out of balance," Segre says.
What a neat way to think about disease! But my next question was, why haven't we figured this out before? Not to worry, NPR addressed that too:

Considering that the field of microbiology is more than 100 years old, one might think scientists would have discovered all this long ago. But the problem has been that 99 percent of skin bacteria don't grow in the laboratory, so scientists couldn't identify them. Now, they can fingerprint bacteria's DNA and identify specific species. And that's opened up a whole new world.
Given the enormous variety of bacteria catalogued in this latest "population census," NPR says, it's likely that the bacteria in total have far more genes than we do.