Auxotrophy
Auxotrophy (
Prototrophic cells (also referred to as the 'wild type') are self-sufficient producers of all required metabolites (e.g. amino acids, lipids, cofactors), while auxotrophs require to be on medium with the metabolite that they cannot produce.[1] 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.[2]
Replica plating is a technique that transfers colonies from one plate to another in the same spot as the last plate so the different media plates can be compared side by side. It is used to compare the growth of the same colonies on different plates of media to determine which environments the bacterial colony can or cannot grow in (this gives insight to possible auxotrophic characteristics. The method of replica plating implemented by Joshua Lederberg and Esther Lederberg included auxotrophs that were temperature-sensitive; that is, their ability to synthesize was temperature-dependent.[3] (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.[4]
Applications
Genetics
In
Researchers have used strains of
Many living things, including humans, are auxotrophic for large classes of compounds required for growth and must obtain these compounds through diet (see
The complex pattern of evolution of vitamin auxotrophy across the
The Mutagenicity test (or Ames test)
The Salmonella Mutagenesis test (
Auxotrophy-based methods to incorporate unnatural amino acids into proteins and proteomes
A large number of unnatural amino acids, which are similar to their canonical counterparts in shape, size and chemical properties, are introduced into the recombinant proteins by means of auxotrophic expression hosts.[9] For example, methionine (Met) or tryptophan (Trp) auxotrophic Escherichia coli strains can be cultivated in a defined minimal medium. In this experimental setup it is possible to express recombinant proteins whose canonical Trp and Met residues are completely substituted with different medium-supplemented related analogs.[10] This methodology leads to a new form of protein engineering, which is not performed by codon manipulation at the DNA level (e.g. oligonucleotide-directed mutagenesis), but by codon reassignments at the level of protein translation under efficient selective pressure.[11] Therefore, the method is referred as selective pressure incorporation (SPI).[12]
No organism studied so far encodes other amino acids than the canonical twenty; two additional canonical amino acids (selenocysteine, pyrrolysine) are inserted into proteins by recoding translation termination signals. This boundary can be crossed by adaptive laboratory evolution of metabolically stable auxotrophic microbial strains. For example, the first clearly successful attempt to evolve Escherichia coli that can survive solely on the unnatural amino acid thieno[3,2-b]pyrrolyl) alanine as the only substitute for tryptophan was made in 2015.[13]
In popular culture
The 1993 film Jurassic Park (based on the 1990 Michael Crichton novel of the same name) features dinosaurs that were genetically altered so that they could not produce the amino acid lysine.[14] This was known as the "lysine contingency" and was supposed to prevent the cloned dinosaurs from surviving outside the park, forcing them to be dependent on lysine supplements provided by the park's veterinary staff. In reality, no animals are capable of producing lysine (it is an essential amino acid).[15]
See also
Footnotes
- )
- ^ ISBN 9780122270802.
- PMID 14927572.
- ^ Griffiths, Anthony J.F.; Miller, Jeffrey H.; Suzuki, David T.; Lewontin, Richard C.; Gelbart, William M. (2000). "Mutant types".
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(help) - PMID 23623319.
- ^ a b Ahern, Kevin (2017). Biochemistry Free for All. DavinciPress.
- PMID 768755.
- PMID 25435356.
- PMID 14662389.
- S2CID 42436705.
- S2CID 2887572.
- .
- PMID 26136259.
- ^ Coyne JA (10 October 1999). "The Truth Is Way Out There". The New York Times. Retrieved 2008-04-06.
- S2CID 1870305.
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"