Bacteria are single-celled organisms. Some play in important role in decomposing organic matter, and others produce natural antibiotics that inhibit disease organisms. Many types of beneficial soil bacteria are able to absorb nitrogen from the air and when they die, they make the nitrogen available to plants. Peas and beans are two of the many kinds of plants that require nitrogen-fixing bacteria for healthy growth. Compost is rich with beneficial, disease-suppressing microorganisms that help to keep pathogens under control.
Organic matter is what they eat.
You can provide it in the form of compost, rotted manure, cover crops, shredded leaves, or natural fertilizers such as cottonseed meal, fish emulsion, kelp and alfalfa meal. It's hard to add too much organic matter. Give Them Air. Most soil organisms need oxygen to survive. To keep your soil light and fluffy, add organic matter and avoid walking around on it, especially in the spring when it's still very wet.