Tuesday, November 20, 2012

Microbiome Part 8: Human Symbionts

Note: This program first aired on November 7, 2012.

Most of us can accept and understand, perhaps subconsciously, that our guts are full of bacteria, and that those bacteria help digest our food.  We’ve talked about this in recent weeks and it is a concept most of us are comfortable with: If there are bacteria on our bodies, your gut, that wild independent ecosystem within you, is exactly where you would expect them to be.

The problem is, our gut isn’t the only place bacteria live on our bodies, and digesting food isn’t the only thing they do for us. Human beings have literally been described as mammal/bacterial symbionts,  organisms completely and utterly at the mercy of the symbiotic relationship they have evolved with microscopic partners over millions of years, organisms that are actually collections of trillions of organisms—one big one and billions of little ones. One source even calls it “the human super organism”. Now to be fair, I am sure this symbiosis is not limited humans, though I am not familiar with studies of the microbiome of the domestic house cat, or the elephant, or of dolphins ( as a side note: It is very likely that this research has been done, or at least proposed). I think that when we look closely, we realize that our definition of life as we know it has to change. We find that without exception what we used to call an individual organism is in fact an accumulation of organisms working in concert. Its true: no man is an island. And nature isn’t red in tooth and claw, its symbiotic.

So when you look at the human organism, you find bacteria not only in the gut, but everywhere else on the body as well. And just like in the gut, these bacteria in all the other places in our body are doing a job for us. An excellent example is on our skin. We are covered head to toe with bacteria, and amazingly it is not a homogeneous community. I remember being amazed by some of the first research that came out on the human microbiome; it outlined the discovery that the bacteria on your right hand are a completely different community than the bacteria on your left hand. Each area of the body is a distinct ecological niche for our bacterial partners.

The bacteria on our skin play a similar role to the bacteria in our gut, in that they help prime the immune system, keeping it at the ready without stimulating full blown activation. More interestingly they seem to regulate their own community with the checks and balances we see in any ecological system. For example Staphylococcus epidermis is a very common skin bacteria (hence the epidermis name), and while generally innocuous, can result in some nasty infections, especially in the immunosuppressed or otherwise ill. There is evidence though, that it also secretes antibiotic compounds (endogenous antimicrobial peptides to be exact); these compounds are the bacteria’s own chemical warfare against competing bacteria. Many other sampled skin bacteria do the same. Their infighting is our benefit, by releasing all these anti biotic compounds on our skin, they keep each other in check, never allowing one type to grow to the point of becoming pathogenic. That is why you should go easy on the hand sanitizer and antibacterial soap. These products can disrupt the balance of bacteria on the skin, and lead to more pathogenic bacteria in the long run.

So our coconspirators in this thing we call the human superorganism not only keep our immune system tuned and ready for action, they also police themselves, to our benefit. When their balance gets disrupted, by antibiotics, ultra clean living or some other environmental insult, or when you get dealt a weak hand (coming out the sun roof instead of the “normal way” is a fast and sure way to start out life with a microbiome deficit) your microbiome is less able to manage itself, leading to dysbiosis and a whole host of illnesses. So don’t micromanage your microbiome. Let them do their work and attend to their own bacterial business.  In most instances, you’ll be better off for it.


Check out the good work by the folks at the Human Food Project: http://humanfoodproject.com/

The title of Michael Specter’s article in the Oct 22, 2012 New Yorker says it all: “Germs are Us”—if you haven’t read it, run out and get it. It will make you want the Heliobacter pylori bacteria in your stomach!

Lynn Margulis was really on to something when she wrote Symbiotic Planet (1998 Basic Books ISBN 0465072712)

“The skin’s secret surveillance system” Nature July 26, 2120 http://www.nature.com/news/the-skin-s-secret-surveillance-system-1.11075

Great article from Germany’s Spiegel “Western Lifestyle Disturbing Key Bacterial Balance” 9/21/2012 http://www.spiegel.de/international/zeitgeist/western-lifestyle-leading-to-dangerous-bacterial-imbalances-a-856825.html

On the skin biome—“Skin microbiota: a source of disease or defense?” From the British Journal of Dermatology, March 2008 http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2746716/