Less Than One Percent Human

There are 100 trillion microbes living inside of you. That's ten times the number of human cells in your body. And together, those microbes have more than three million genes--150 times the number of "human" genes in your body. If you assembled a genetic senate, your own DNA would have to fight for a single seat. Maybe we aren't quite as human as we thought.

I'm in Washington, DC, scouting for future stories for NOVA at the annual meeting of the American Association for the Advancement of Science. (That's a mouthful, so I'll just say AAAS from here on out). The AAAS brings scientists, policymakers, and journalists together for a long weekend of talks, public events, lots and lots of coffee, and--as I learned in one set of talks this morning--lots and lots of microbes. The AAAS attracts about 8,000 human attendees, so that makes eight hundred thousand trillion (80 quadrillion!?) microbes attendees.

But the human microbiome is under attack. Antibiotics, supplements, fad diets, fatty "Western" food, and behaviors and environmental factors we probably don't yet understand all put stress on the microbes that live in the human body. Scientists like David Relman (Stanford University) are trying to find out exactly what we're doing to our local microbes, and how quickly and robustly they bounce back from wallops like antibiotics.

Meanwhile, other researchers hope to develop new drugs that target microbiota instead of human cells. As Jeremy Nicholson of Imperial College London puts it: "Drug the bugs!"

Drugging the bugs could be a pharmacological windfall, says Nicholson, because the microbiome presents such a rich and varied--and as-yet untapped--set of targets. There's reason to expect that the microbiome is a powerful player in human health, Nicholson points out, because researchers have already found some evidence for connections between the microbiome and autoimmune disease, colon cancer, allergies, and perhaps even autism, high blood pressure, and obesity. (Nicholson has worked with Nestle on the development of baby formula spiked with "good bacteria," or probiotics.)

This adds a new dimension to the old "nature versus nurture" debate. No more genetic determinism, says Nicholson: Our genome, epigenome, and microbiome are all in conversation with each other and with our environment. Disentangling the threads of that conversation is tricky; to do so in a controlled setting, researchers sometimes transplant human microbiomes into germ-free mice, test out different diets or medicines on the mice, and then sample how each mouse's microbial population changes over time.

One way to rebuild a crippled microbiome might be a fecal transplant, which is exactly what it sounds like. Some doctors are already experimenting with this therapy (also known as bacteriotherapy) for certain infections, ulcerative colitis, and even diabetes and Parkinsons disease. The results so far are promising, but anecdotal.

Maybe it's a little gross. Maybe you are wishing that you hadn't read this while eating breakfast. But however you feel about the "trillions of friends" that make up your microbiome, one thing is sure: As Relman says, "You're never alone."

User Comments:

That's Cool in so many dimensions! One of which is that our multi-celled body of independently living organisms can combine to create a single consciousness.

what happens to my microbes if i was a animal and i was eaten? are they destroyed by the body or are they used again?

This is a fascinating topic. Certainly these microbes are not merely passive residents, but must affect us in many as yet unknown ways. It is common for puppies to eat poop, a behavior that most will outgrow in adulthood. I've always believed that this was beneficial to them as a way to acquire the intestinal flora of their parents.

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