Mutation auxotrophic

Chu, E. H. Y., Brimer, P., Jacobson, K. B., and Merriam, E. V. (1969), Mammalian cell genetics I. Selection and characterization of mutations auxotrophic for L-glutamine or resistant to 8-azaguanine in Chinese hamster cells in vitro. Genetics 62, 359-377. 

Many kinds of amino acids (eg, L-lysine, L-omithine, t-phenylalanine, L-threonine, L-tyrosine, L-valine) are accumulated by auxotrophic mutant strains (which are altered to require some growth factors such as vitamins and amino acids) (Table 6, Primary mutation) (22). In these mutants, the formation of regulatory effector(s) on the amino acid biosynthesis is genetically blocked and the concentration of the effector(s) is kept low enough to release the regulation and iaduce the overproduction of the corresponding amino acid and its accumulation outside the cells (22). 

Mutation. For industrial appHcations, mutations are induced by x-rays, uv irradiation or chemicals (iiitrosoguanidine, EMS, MMS, etc). Mutant selections based on amino acid or nucleotide base analogue resistance or treatment with Nystatin or 2-deoxyglucose to select auxotrophs or temperature-sensitive mutations are easily carried out. Examples of useful mutants are strains of Candida membranefaciens, which produce L-threonine Hansenu/a anomala, which produces tryptophan or strains of Candida lipolytica that produce citric acid. An auxotrophic mutant of S. cerevisiae that requires leucine for growth has been produced for use in wine fermentations (see also Wine). This yeast produces only minimal quantities of isoamyl alcohol, a fusel oil fraction derived from leucine by the Ehrlich reaction (10,11). A mutant strain of bakers yeast with cold-sensitive metaboHsm shows increased stabiUty and has been marketed in Japan for use in doughs stored in the refrigerator (12). 

Since auxotrophic mutants and regulatory mutants are widely used in the overproduction of amino adds, this can be a severe problem. In nature, mutation always takes place but this takes some time. However, in fermentation many generations are produced in a relatively short period of time and the chances of back mutation are enhanced. 

Addition of antibiotics to the fermentation broth may be used to avoid problems associated with growth revertants (eg auxotrophic back mutation) ensure that genetic material (eg plasmid DNA) is maintained within the process micro-organism. 

Auxin-like herbicides, 13 305 Auxins, 13 35, 38, 284, 304 Auxochromes, 19 425 Auxotrophic mutations, in yeast,... 

Prokaryotes are sensitive towards aminoglycosides. In E. coli sublethal levels suppress auxotrophic mutations and increase the frequency of misincorporation obtained in vitro (Gorini and Kataja 1964 Davies et al. 1965). Yeast is normally quite resistant toward aminoglycosides, but mutant strains expressing translational suppressors display increased sensitivity in vivo and increased mistranslation frequencies in vitro (Palmer et al. 1979 Singh et al. 

Tosk, J., Schmeltz, I. Hoffmann. D. (1979) Hydrazines as mutagens in a histidine-requiring auxotroph of Salmonella typhimurium. Mutat. Res., 66. 247-252... 

The investigation of an amino acid biosynthetic pathway in E. coli begins with the accumulation of mutants that are deficient in the capacity to synthesize that amino acid. Mutants of this sort are known as auxotrophs. Each auxotroph bears a mutation in one of the genes that encodes an enzyme required for a step in the biosynthetic pathway of the amino acid. It is possible to determine how many steps are in a particular pathway by the process of complementation analysis (see fig. 11.14). 

Put selective pressure against plasmid-free cells using ctuxotrophic mutants or antibiotic-resistant plasmids (Parker and DiBiasio, 1987). Auxotrophic mutant is the cell which is mutated so that it requires a specific growth substance beyond the minimum required for normal metabolism and reproduction. 

Fungi Mutation Saccharomyces cerevisiae Reversion of auxotrophic mutations (e.g. ilv in strain D7 several in strain XV185-14C) Point mutations <3 -wk L L S-M NA... 

Auxotroph. A mutation that causes a defect in the synthesis of an essential metabolite such that the growth of the organism is dependant on exogenous supply of this metabolite. 

Tannoka H. 1977. Development and application of Bacillus subtilis test systems for mutagens, involving DNA-repair deficiency and suppressible auxotrophic mutations. Mutat Res 42 19-32. 

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