Organisms that derive their energy and carbon by consuming organic compounds synthesized by other organisms rather than producing their own organic matter from inorganic sources.
Explanation
The term heterotroph comes from the Greek for “other feeder.” Unlike autotrophs, which fix carbon dioxide into organic molecules using energy from light or inorganic chemical reactions, heterotrophs must obtain preformed organic molecules for both carbon and energy. They metabolize carbohydrates, lipids and proteins produced by plants, algae or other organisms through processes such as aerobic respiration, anaerobic respiration and fermentation. Heterotrophic metabolism is widespread across domains of life, encompassing animals, fungi, many bacteria, archaea and protists.
Heterotrophs can be categorized by their energy source. Chemoheterotrophs obtain energy by oxidizing organic compounds; this group includes humans, other animals, fungi and most pathogenic bacteria. Photoheterotrophs use light to generate ATP but rely on organic carbon sources; examples include certain purple non‑sulfur bacteria and marine planktonic microbes. Ecologically, heterotrophs occupy the consumer and decomposer levels of food webs. Primary consumers, such as herbivores, feed on autotrophs; secondary and tertiary consumers feed on other heterotrophs; decomposers such as saprophytic fungi and many bacteria break down dead organic matter and recycle nutrients. Heterotrophic microorganisms play key roles in biogeochemical cycles by decomposing organic material and mineralizing nutrients. In microbiology, heterotrophy is contrasted with autotrophy to classify metabolic strategies and growth requirements of microbes.
Examples and Ecological Roles
All animals are chemoheterotrophs, obtaining organic nutrients from plants or other animals. Fungi such as molds and mushrooms secrete enzymes to digest complex polymers in dead wood and leaf litter, absorbing the resulting simple sugars and amino acids. Protozoa, including amoebae and ciliates, consume bacteria and other small organisms. Many bacteria, such as Escherichia coli, Staphylococcus aureus and Mycobacterium tuberculosis, are heterotrophic, requiring organic carbon sources for growth. Photoheterotrophic bacteria like Rhodospirillum rubrum and some members of the SAR11 clade use light to supplement their energy but cannot fix carbon dioxide. In ecosystems, heterotrophs drive nutrient cycling and energy transfer by feeding on producers and each other and returning carbon dioxide and inorganic nutrients to the environment through respiration and decomposition.
Heterotrophy is a fundamental nutritional strategy that links organisms within food webs and connects biological metabolism to global cycles of carbon and nutrients.
Related Terms: Autotroph, Chemoheterotroph, Photoheterotroph, Food web, Saprophyte