bacteria that use organic (carbon-containing) compounds as a source of energy and carbon. This characteristic distinguishes heterotrophic bacteria from chemoautotrophic (chemosynthesizing) and photoautotrophic (photosynthesizing) bacteria, which assimilate CO₂ as a source of carbon. The overwhelming number of known species of bacteria, both aerobic and anaerobic, are heterotrophic. Many heterotrophic bacteria utilize sugar, alcohol, and organic acids. However, there are specialized heterotrophic bacteria capable also of decomposing cellulose, lignin, chitin, keratin, hydrocarbons, phenol, and other substances. Heterotrophic bacteria are found widely in soil, water, foods, and the bed soil of bodies of water. Heterotrophic bacteria take an active part in the natural recycling of substances.