In order to better understand how the microbiome is essential to life, we can look at what happens to animals without microbiomes.
In controlled laboratory conditions, animals are tested that have never been exposed to bacteria. Even the food they eat is sterilized. These animals are known as “sterile animals." These sterile animals are compared to ordinary mice in many different studies.
While the sterile mice do survive, their intestines do not fully develop. The surface area of their intestines is smaller. This limits their ability to absorb nutrients and unwanted substances can “leak” out of the intestines into the bloodstream. Additionally, the intestinal blood vessels are thinner.
Once sterile mice are given intestinal bacteria, their health improves. The bacteria activate genes in the mouse that help absorb nutrients, improving the barrier between the intestine and blood. In other words, the bacteria allow the mouse to build healthy intestines through the mouse's own genes. Indirectly this helps develop the body's organs.
Scientists are learning more every day about the microbiome and how it plays so many important roles in regulating our body systems.