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Auxotrophy ([αὐξάνω] Error: {{Langx}}: text has italic markup (help) "to increase"; τροφή "nourishment") is the inability of an organism to synthesize a particular organic compound required for its growth (as defined by IUPAC). An auxotroph is an organism that displays this characteristic; auxotrophic is the corresponding adjective. Auxotrophy is the opposite of prototrophy, which is characterized by the ability to synthesize all the compounds needed for growth.

Prototrophic cells (also referred to as the 'Wild Type') are self sufficient producers of required amino acids, while auxotrophs require to be on medium with the amino acid that they cannot produce . It is a term generally used in relation to something, for example saying a cell is methionine auxotrophic means that it would need to be on a medium containing methionine or else it would not be able to replicate. In this example this is because it is unable to produce its own methionine (Methionine Auxotroph). However, a prototroph or a methionine prototrophic cell would be able to function and replicate on a medium with or without methionine.

The method of replica plating implemented by Esther Lederberg included auxotrophs that were temperature-sensitive; that is, their ability to synthesize was temperature-dependent. (Auxotrophs are usually not temperature-dependent. They can also depend on other factors.) It is also possible that an organism is auxotrophic to more than just one organic compound that it requires for growth.

Auxotrophy in Genetics

In genetics, a strain is said to be auxotrophic if it carries a mutation that renders it unable to synthesize an essential compound. For example, a yeast mutant with an inactivated uracil synthesis pathway gene is a uracil auxotroph (e.g., if the yeast Orotidine 5'-phosphate decarboxylase gene is inactivated, the resultant strain is a uracil auxotroph). Such a strain is unable to synthesize uracil and will only be able to grow if uracil can be taken up from the environment. This is the opposite of a uracil prototroph, or in this case a wild-type strain, which can still grow in the absence of uracil. Auxotrophic genetic markers are often used in molecular genetics; they were famously used in Beadle and Tatum's Nobel prize-winning work on the one gene-one enzyme hypothesis.

Researchers have used strains of E. coli auxotrophic for specific amino acids to introduce non-natural amino acid analogues into proteins. For instance cells auxotrophic for the amino acid phenylalanine can be grown in media supplemented with an analogue such as para-azido phenylalanine.

Many living things, including humans, are auxotrophic for large classes of compounds required for growth and must obtain these compounds through diet (see vitamin, essential nutrient, essential amino acid, essential fatty acid).

The complex pattern of evolution of vitamin auxotrophy across the eukaryotic tree of life is intimately connected with the interdependence between organisms.

Application

The Mutagenicity Test (or Ames Test)

The Salmonella Mutagenisis test (Ames test) uses multiple strains of Salmonella typhimurium that are auxotrophic to histidine to test whether a given chemical can cause mutations by observing its auxotrophic property in response to an added chemical compound. The mutation a chemical substance or compound causes is measured by applying it to the bacteria on a plate containing histidine then moving the bacteria to a new plate without sufficient histidine for continual growth. If the substance does not mutate the genome of the bacteria from auxotrophic to histidine back to prototrophic to histidine, then the bacteria would not show growth on the new plate. So by comparing the ratio of the bacteria on the new plate to the old plate and the same ratio for the control group, it is possible to quantify how mutagenic a substance is, or rather, how likely it is to cause mutations in DNA. A chemical is considered positive for Ames test if it causes mutations increasing the observed reversion rate and negative if presents similar to the control group.

See also

• Autotroph
• Bradytroph

External links

• "Regulation of endosomal clathrin and retromer-mediated endosome to Golgi retrograde transport by the J-domain protein RME-8" - The EMBO Journal
• "Pleiotropic effects of purine auxotrophy inRhizobium meliloti on cell surface molecules" - Springerlink
• "Auxotrophy and Organic Compounds in the Nutrition of Marine Phytoplankton"

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• • • (AMES TEST ADDITION for AMES test wikipage)

• Effect of mutagens on bacteria vs larger organisms
  • It is suggested that if a mutation can arise in bacterial DNA under presence of a mutagen then the same effect would occur for larger organisms causing cancer.
  • Negative Ames Test result suggest that the substance is not a mutagen and would not cause tumor formation in living organisms, however only few of the positive Ames Test resulting chemicals were considered insignificant when tested in larger organisms but the positive Ames Test for bacteria still could not be conclusively linked to expression of cancer in larger organisms. While it can be a possible determinant of tumors for living organisms, humans, animals, and so on, more studies must be completed to come to a the conclusion.

The unsolved mysteries of life are themselves an answer to the question of human curiosity.