My Microbes Made Me Do It!

So far as I know, and Google backs me up on this, no one has used this as their defense in a criminal trial; however I’m confident that with our ever creative legal system its time will soon come. A number of years back there was the ‘Twinkie defense’ where the defendant claimed that his addiction to junk food made him depressed and ultimately homicidal (this was the famous Harvey Milk case). Based on new research, this actually could have been a ‘microbes made me do it’ case. There have been several recent studies that have linked high sugar diets with the production by gut microbes of chemicals that affect behavior and cause depression.

In fact, our microbiome is now being cast as a central player not only in human health but also behavior. So what is ‘our microbiome’? Basically it’s the microbes, mostly bacteria (and a surprising number of viruses) that live on, or in us. As scientist’s we often refer to them as ‘host associated’. Microbiologists have known for a long time that humans, other animals, and plants all carried some microbes that were unique and often beneficial to their host. This has been the source of quite a lot of research, but most of it confined to microbiology. In the last 10 years, work started in the 1980’s by a couple of molecular biologists and some microbial ecologists, is finally allowing us to understand just how important and beneficial these associations are.

Today understanding the importance of our microbiome to human health is one of the hottest areas in bio-medicine. I read that one scientist recently likened it to discovering a new essential organ, akin to the liver or kidney, within the human body. Just in the last five years there have been a whole series of discoveries about how our microbes cause us to get fat or stay thin, shape our immune system, change our susceptibility to getting asthma, influence bone density, and almost any other factor related to our health.

One of the most remarkable areas is in behavior. Some scientists have suggested that some neurochemicals that act on our brain are either produced or controlled by the microbes living in our gut. Thus the connection to eating a ‘junk food diet’ that contains large amounts of high fructose corn syrup, sugar, artificial sweetners, etc., that microbes are especially good at metabolizing into chemicals that make you depressed, and perhaps homicidal. I don’t think the ‘kale control’ has been done yet, but it is going to be fascinating to see where all this leads.

In fact, there are lots and lots of controls that have yet to be done in understanding the real importance of the human microbiome to our health. Most of the studies I mentioned above linking the microbiome to different human health facets were actually done in that hardly sapient of creatures, the lab mouse. The bearing of a result in a genetically wacked out mouse living in a cage being fed a controlled diet, to a human being living in the real world should always be taken with some skepticism.

Nonetheless, there have already been some remarkable successes. One particularly nasty microbe Clostridium difficile that causes colitis and serious bowel problems can be cured with that least epicurean of cures, the fecal transplant. It’s just about as gross as it sounds, although I understand you can even take in pill form, flavored versions will probably be available soon. Basically an infected person is implanted with the microbiome of a healthy person (some early trials may have used turkey basters…). Success rates of greater than 80% have been reported, at least double conventional treatments that use antibiotics.

This past week a group of scientists proposed a global microbiome initiative, you can read about in the New York Times, the article has links to proposals published in Nature or Science (good luck getting access). Microbiomes are everywhere, not just in humans. There’s going be more than enough hype to go around, but I’m pretty sure that ultimately how we view the microbiome of whatever biological system that is of interest will change the way we think about biology and the world. As a microbiologist, that’s totally cool, even if my microbes made me say it.

David Emerson

About David Emerson

David Emerson is a professional scientist at the Bigelow Laboratory for Ocean Sciences who studies bacteria that live literally between a rock and a hard place. The views expressed here are his alone.