Some bacteria are not only useful, but are essential to life. Organic fertilizers are broken down by bacteria into materials that can be used by plants. Decomposed vegetable and animal matter is thus transformed into nutrients that are absorbed through the roots of other plants. Many species of soil bacteria fix nitrogen; that is, they convert atmospheric nitrogen into nitrates, compounds that are readily absorbed by plants. Some of these bacteria live in colonies in the roots of legumes, such as peas, clover, and alfalfa.
Various commercial processes depend on bacteria. Anaerobic bacteria that ferment certain substances are used in the production of vinegar and some drugs, and in the aging process of cheeses. Some bacteria produce waste products that are useful to humans. One such waste product is lactic acid, which is produced by intestinal bacteria and promotes digestion in humans. It is grown commercially and is added to certain foods such as yogurt.
Bacteria are also used to chemically break down the tough, woody tissues of flax, jute, hemp, and coconut. Modern methods of sewage disposal often make use of bacteria to decompose organic wastes. In a process known as bioremediation, bacteria are added to water or soil to convert toxic pollutants, such as pesticides and oil, into harmless substances. Through genetic engineering, bacteria have been developed for bioremediation and also to produce drugs and other chemicals.