Fully half of the life on Earth, in terms of its weight, is microbial. Billions of bacteria live in the human digestive system. They form over a kilogram of our body weight. These bacteria are referred to as microflora or gut flora and they break down food remains that have not been digested earlier in the digestive system.
They can stop harmful bacteria and fungus from invading the body. In the soil a wide variety of microbes are involved in biodegradation of organic matter, mineralization, root stimulation and pH control. Just as plant roots emit exudates that encourage microbial activity that is beneficial to those plants, the mucus in the human gut feeds beneficial microbes that break down fibers.
In the soil, the micro life in the rhizosphere or root zone makes nutrients available to the plant, just as the gut area in humans makes nutrition available to the human body.