One gram of soil can contain over ten million bacteria. Around the roots of a healthy growing plant a dense coating of microbes may contain a population of from 100 to 200 billion microbes. The life span of a single microbe in this environment is approximately one half hour. Microbes live in colonies and are very mobile. In their rapid life cycle from creation to death they develop tremendous metabolic activity and steadily improve the structure of the soil.
Some microbes excrete antibiotics.
They metabolize phosphorus and iron bonds which are difficult to dilute efficiently without this microbial activity. The earthy odor of the soil is due to them. They create two thirds of the soil carbons, attack cellulose and mineralize nutrients. We have another important grouping of life in the soil. These are mites, nematodes, centipedes, worms, and insects.