What does auxotroph mean?
An auxotroph is an organism, usually a bacterium or fungus, that cannot make one or more substances known as growth factors and must obtain them from its surroundings. In laboratory work, this limitation is deliberately introduced or maintained so that researchers can trace metabolism, identify missing biosynthetic pathways, or select cells carrying particular genes. The term is therefore associated with experimental microbiology and genetics, although auxotrophs also occur naturally. Auxotrophic organisms commonly have requirements for amino acids, vitamins, or purines, depending on the strain and its defects; they are not necessarily dependent on every external nutrient. The related term prototroph describes an organism that does not need a particular growth factor supplied in the medium. Because the contrast is functional rather than a matter of overall nutrition, an auxotroph should not simply be described as an autotroph's opposite: an organism may be self-sufficient for some nutrients while requiring supplementation for others. Auxotroph is most often a count noun, and auxotrophic is the corresponding adjective. The word is specialized, but it names a precise and important laboratory strategy: making a missing capability visible through a controlled nutritional requirement.
nounAn organism, usually a bacterium or fungus, that cannot synthesize one or more growth factors required for growth and must obtain them from its environment or culture medium.
- An organism that requires one or more externally supplied growth factors for growth.
"The researchers used an auxotroph to study the bacterium's amino-acid biosynthesis."
"The strain is an auxotroph, so the culture medium must contain the growth factor it cannot synthesize."
"For yeast genetics, researchers selected an auxotroph that required added leucine."
The regular plural is auxotrophs, with the plural formed by adding -s.
"The researchers compared several auxotrophs under minimal and supplemented conditions."
An auxotroph survives only when the menu includes a growth factor it cannot manufacture—a biochemical neat-freak turned laboratory workhorse.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does auxotroph come from?
Auxotroph combines the combining form auxo-, derived from Greek auxanō, meaning “to grow or increase,” with -troph, based on Greek trophos, “one who feeds or nourishes.” The term belongs to modern biological and biochemical usage, particularly the study of microorganisms and their nutritional requirements. Its relatives include autotroph and heterotroph, while trophic comes from the same Greek root associated with nourishment or feeding.
Related word forms
How auxotroph is actually used
This is specialized terminology used chiefly in microbiology, genetics, and biochemistry. It is usually a count noun, while auxotrophic is the corresponding adjective.
Easily confused with auxotroph
An autotroph obtains carbon from inorganic sources such as carbon dioxide, whereas an auxotroph is defined by needing an externally supplied growth factor; the two classifications can overlap.