Wednesday, 18 October, 2017

Our Physiological Microbiome

The human physiology is a remarkable piece of creation, with its inbuilt adjustment mechanisms for living in a hostile world from the days of our forefathers to our present chemical environment. Its capacity to survive the numerous earthly pathogens is legend, and the more we understand its functional abilities, the more surprises we learn about its wonderful modality.

As an embryo, our nutrients were delivered through a narrow layer of cells call a syncytiotrophoblast, which lay between the placenta and our mother’s uterus. To make such a food delivery system, the mother required a gene to express a protein called syncytin. It turns out that this gene is not human, but rather a long ago domesticated virus which now sits in the human genome that is producing this vital ingredient.

Certain viruses, called retroviruses, have the ability to insert themselves into our DNA. But sometimes retroviruses get into eggs, which we call the germline. Once fertilized, these eggs give rise to whole bodies, so the virus is now in all the cells of the body. It is now called an endogenous retrovirus. Over time, the virus becomes part of our genome. Imagine the surprise of the scientific community as we began large sequencing projects such as the Human Genome Project, and we realize that as much as 8% of our genome is viral in origin.

In the months leading to our birth, the ecological landscape that was our mother, changed, and bacterial communities that are part of her gut migrated to her birth canal. Because as we were being born, assuming it was not a Cesarean section, our mother inoculated us with billions of bacteria, of many different species. What she was doing, albeit without knowing it, was the ultimate in probiotics. Placing bacteria that would benefit us as we grew. Failure to seed us with microbes has costs. Increasingly, studies are showing how kids delivered by Cesarean lack important good bacteria; leading to increased problems, such as asthma, and possibly even autism, although much more evidence is required to establish this.

But our mother’s efforts did not stop there. If we were breast fed, our mother spent 15 to 20% of the energy required to make the milk with the bacteria she inoculated us with. Human mothers produce human milk oligosaccharides, or HMOs, which are completely indigestible by children. What these HMOs do is provide a growing surface for a special bacterium called bifidobacterium longum, subspecies infantis. These are good bacteria, and can only grow when given HMOs. And the consequence of having these bacteria in our growing gut, is a better immune system, less allergies, stronger bones, and higher IQ.

Human mothers have fostered a pact with bacteria that help their children grow healthy and strong. Breast milk really is best. What science has been discovering over the last five to ten years is that our bodies are ecological landscapes for billions of bacteria; if you were to collect them all and weigh them, it would be around 3.5 to 5.0 pounds or 1.6 to 2.3 kilograms of bacteria. That is heavier than our brain. Bacteria living in and on our body outnumber our cells ten to one. The genes of bacteria outnumber human genes 200 to one. The whole community is called the microbiome. Yaks, we may say, but that is part of the reason we may be healthier as a result of our bacterium community.

Credit: Summarised from COURSERA’s Epidemics, conducted by the Pennsylvania State University.