A Brave New World: You
The Pasteurian Revolution of the 1800’s heralded in a new paradigm of disease. Previously unexplained health phenomena could now be shown to be derived from “germs” – microorganisms invisible to the naked eye. The term “germ” quickly took on a negative connotation and until recently the microbial world has been seen primarily as a breeding ground for invisible enemies to human health. Its pretty incredible actually, the distaste the word “bacteria” instills in us, when really, it simply refers to a domain of prokaryotes. So, is the entire microbial world bent on our demise? I think the answer to this question can be summed up in one simple statistic:
Inside of you there are 1013 human cells and 1014 bacteria cells.
In other words, for every one cell of you there are ten that are not you…Wait, what? The first question this recent discovery may fuel is a stumbled WHAT? But lets digress for a moment and ask, why?
The initial visceral curiosity here arises from one major assumption that the Western psyche makes about the world, that I am an individual and am derived in my current form from the process of competitive selection. The reality however, is that none of us are individuals and we are all derived not just from natural selection, but from collaborative efforts between tens of thousands of species of organisms acting in symphony to produce the emergent concert that is: us. That may be a bit heavy. Let me explain.
Again, there are ten times the number of bacterial cells throughout the human body and they are mostly centralized to the digestive tract. This internal ecosystem of microbial flora is referred to as one’s “microbiome”. Each person’s microbiome is different, in a similar way that we are all different. The distribution of species in the digestive tract reflects one’s life experiences, adventures and location of upbringing. For example, the typical gut flora of a person raised in the United States has more bacteria specialized in processing fat and protein. This is in part why people immigrating to the United States often have problems with gaining weight in the first few years, because their microbial counterparts are ill-equipped at handling the amount of fat in American foods.
Another astonishing example of this “microbial footprinting” is in the microbiomes of people who have lived their entire lives in Japan where seaweed is a dietary staple. Throughout the world the microbe Bacteroides plebeius has been observed in the gut of various people. Curiously however, the B. plebeius microbe in some Japanese people has incorporated a gene passed to it, via horizontal gene transfer, from Zobellia galactanivorans, a marine bacterium. The gene in the Japanese form of B. plebeius expresses enzymes specializing in the degradation of certain polysaccharides found in seaweed. Implications for the exhausted “Nature vs. Nurture” debate abound, these findings are Earth-shattering in more ways than the hands can hold. Oh, by the way, this doesn’t stop at digestion.
The real sexy aspect of this new vein of research is the implications for the behavioral sciences. In 2011, a series of papers came out linking a lack of adequate gut microbial populations to an anxiety disorder. Researchers raised a brood of mice in a germ-free environment, i.e. from birth they had little to no exposure to the typical microbial populations they may encounter, and the results were a bit unsettling. The researchers noted significant defects in the development of the Amygdala which subsequently showed in behavioral studies that the sterile mice had major issues with anxiety and depression. In another similar study, it was shown that feeding normal mice probiotic bacteria significantly reduces depression-like behavior.
Right now, this is the biggest emerging area of research worldwide. Finally, the notion that we are not individuals, but emergent structures of ecosystems is taking hold. The result of such novel understanding is entirely uninformed and preemptive attempts at targeting this new world to cure and change. Currently, probiotic medicines are starting to crop up, each of which will soon be shown to have more “side effects” than efficacy in the expected. When we make a discovery, we immediately assume we understand how to manipulate the system, unaware of how the vastly complex structures we are changing. We are always confidently overzealous. These recent discoveries are awesome, they really are, but I want to stress that we cannot let our zeal overtake us. This time around, we must admit a lack of understanding and re-realize the feeling of awe. Again, upwards of 40,000 different species of bacteria, right inside of you, are talking to one another; buffering carcinogens and reward hormones, digesting cellulose, fermenting, interacting in ways we really will never know although they may be helping “us”!
“We” would not be alive if it were not for our microbial brethren. Let me pose this question: Is taking the step to understand this internal ecosystem the next step in consciousness. Until now, we have had a very elementary understanding of who we are and why we are who we are. Is this the next step?
– Jesse Bryant
Animals in a microbial world, a new imperative for the life sciences – McFall-Ngai et al. 2012 PNAS
Mood and gut feelings – Forsythe et al. 2009 Elsevier
An ecological and evolutionary perspective on human-microbe mutualism and disease – Dethlefsen et al. 2007 Nature