Look at any large organism – your favorite tree in the yard, your dog or cat or yourself in the mirror. The actions of that organism are based not only on the actions of the cells and tissues that make it up, but also on the actions of microbes living on and in that organism. In fact, the microbes we carry outnumber our own cells by 100-fold or more.
As a microbiologist, I have a vested interest in very tiny organisms. I enjoy trying to figure out the many ways that they make a living and respond to their environment. That said, we all have a vested interest because many of our bodily processes are due in part or to the actions of the microbes that live on our skin and throughout our gastrointestinal tract. All large organisms, animals, plants, fungi and algae, have their own distinctive collection of microbes called its microbiota. The collective actions and synergisms of the host and its microbiota are so intertwined that we need a new term, holobiont, to acknowledge its complexity.
Over the past several years, I have worked with Hiram students on the microbiota on the surface of corn leaves, both healthy and nutritionally starved, and on the microbiota within the gut of crickets fed diets with differing amounts of bitter tannins (what makes coffee or tea bitter). The genomic revolution in biology has provided us with new tools to identify the diversity of microbes living in a particular place and to infer their major metabolic processes.
As you might suspect, the human microbiota has received the lion’s share of research attention and the findings of that research has tremendous implications for the future of human health and what it truly means to be human. This will be the subject of a biomedical humanities course I am teaching this semester: “You and Your Microbes”. Let me give you a few examples of what we will cover.
- A baby’s first poop can tell you how it was delivered. Dominguez-Bello and coworkers (Proc. Natl. Acad. Sci. USA, 2010) sampled the mouth, skin and vagina of mothers just prior to delivery and then sampled the first poop of their babies. The gut microbiota of babies delivered vaginally was most similar to the microbiota of the mother’s vagina, while C-section babies have a gut microbiota most similar to mom’s skin. Your first inoculation of microbes into your gut is from your mother as you enter the outside world.
- Deodorant matters. In an experiment I did right here at Hiram College with nursing students in my Medical Microbiology course, we tested the impact of deodorant on the microbiota of the human armpit. My wife Asha grudgingly agreed to let me go two weeks with no soap on the armpits during showers, just water. I then put deodorant on the right armpit but not on the left. It felt very strange. After two weeks, I swabbed each armpit and students isolated DNA from the microbial samples and we obtained DNA sequence data. What we found (see figure to the right) was the impact of deodorant on the microbiota was massive but not indiscriminate. Deodorant treatment decreased the overall microbial community by 84 percent, but its impact on the community composition was even greater. Staphylococcus and its relatives dominate the armpit normally, but really take it on the proverbial chin with the application of deodorant. Corynebacterium and relatives go from a tiny fraction of the untreated community to almost three quarters of the treated community. Research indicates that both Staphylococcus and Corynebacterium contribute to human body odor but in different ways (Barzantsky et al., J. Biotechnology, 2012; Hara et al., PLoS One, 2014).
- Your microbiota impacts your metabolism. We have all heard someone say about a friend or family member, “He eats well and still gains weight; he must have a slow metabolism.” What does that mean? It cannot mean that he doesn’t break down his food efficiently because then he would lose weight. If anything, he might be absorbing more of the calories he has eaten than the average person. That can have some basis in a person’s own genetics, but it can also involve the gut microbiota. In a beautiful set of experiments (yes, there is beauty in science), Ridaura and coworkers (Science, 2013) studied human twins where one twin was lean and the other was obese by one or more criteria. Gut microbes from stool samples of each twin were inoculated into the guts of previously germ-free mice. Even though they were fed the same diet, mice with the obese twin gut microbiota put on significantly more weight than the mice with the lean twin gut microbiota. Taking it even further, the researchers found that when mice with the different microbiota were housed together, the mice with the obese twin gut microbiota did not put on as much weight. The lean microbiota had infiltrated the obese microbiota and won. The movement of the microbes was probably due to the co-grooming of the mice and the fact that they might eat some poop. What these means for you and me is that changing our gut microbiota can give us a chance to lose some weight if diet and exercise are not enough.
You are more than just you – your microbiota matters.