Auxotroph

An auxotroph is a mutant that requires a factor for growth that is not required by the wild-type. The opposite of an auxotroph is a prototroph, an organism that grows in minimal medium containing only inorganic salts and a carbon source (plus an additional energy source if the organism is an autotroph). Typical auxotrophic mutations are in genes encoding biosynthetic enzymes for amino acids, vitamins, and nucleotides. Some organisms are natural auxotrophs. For example, humans require that all vitamins and several amino acids be supplied in their food. In contrast many, but not all, free-living microorganisms, such as Escherichia coli, are prototrophs. A specific auxotrophic phenotype is called an auxotrophy, eg, an arginine auxotrophy, and the mutant is called an arginine auxotroph.