We know that productive garden soil contains between 100 million and 1 billion bacteria per gram (about a teaspoon full). We also know that many of these bacteria have important roles to play in the Soil Food Web and are to a great degree orchestrated by plants through plant root exudates. What we don't know is what roles many of the different bacteria play. We know about a small fraction of them that help with nutrient cycling, disease suppression, and are important to water dynamics in the soil but the greater number by far and their related interaction with other organisms is currently beyond our understanding. In 2007, Christopher Lowry, a neuroscientist now at the University of Colorado found that certain strains of soil-borne bacteria sharply stimulated the human immune system. One bacteria, however, Mycobacterium vaccae, has been found to have amazing benefits to us directly.
Mycobacterium vaccae, a bacteria that is common in soil, has been found to activate a specific group of neurons in our brains that produce serotonin. Serotonin is found in the brain and the blood and is a very important neurotransmitter which helps regulate a whole host of functions including:
coping responses to stress
Dave The Garden Guy 5/23/11